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STRATEGIES FOR SOUND

MASKING

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2 May 2016

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Contents 5

Part One Specifying and procuring sound masking systems

By Niklas Moeller, MBA

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Part Two

Providing acoustic comfort with sound masking

By Niklas Moeller, MBA

21

Part Three Understanding acoustic privacy within the built environment

By Niklas Moeller, MBA

30

Part Four

Sound advice on speech privacy

By Sean D. Browne

36

Part Five

Selecting the right ceiling for an office

By Chris Marshall

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Š 2016 Kenilworth Media Inc. All rights reserved.

Strategies for Sound Masking Part One Specifying and procuring sound masking systems

BY NIKLAS MOELLER, MBA

Niklas Moeller, MBA, is vice-president of K.R. Moeller Associates Ltd. (Burlington, Ont.), a global developer and manufacturer of sound masking systems for more than 30 years. He has been in the sound masking business since 1998.

Moeller writes an acoustics blog at soundmaskingblog.com.

He can be reached via e-mail at nmoeller@logison.com.

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Photo © Zahid Ghafoor. Photo courtesy K.R. Moeller Associates Ltd.

Sound Advice

Specifying and procuring sound masking systems

By Niklas Moeller, MBA

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veryone has heard the old adage “silence is golden,” but just as with lighting and temperature, the comfort zone for the volume of sound is actually not zero. In fact, if the background sound level in a space is too low, conversations and noise can easily be heard, even from a great distance, impacting speech privacy and disrupting one’s concentration.

Many organizations use a sound masking system to maintain an appropriate ambient sound level in their facilities, which is typically between 42 and 48 decibels (dB) in commercial interiors. This technology consists of a series of loudspeakers, which are installed in a grid-like pattern in or above the ceiling, and a method of controlling their output. While the sound the loudspeakers distribute has been specifically engineered to increase speech privacy, it also covers up intermittent noises or reduces their impact by decreasing the change between baseline and peak volumes. Although the background sound level is technically higher, occupants perceive the space as quieter. Many systems also provide paging and music distribution, eliminating the need for a separate system.

Types of sound masking systems have been used in various applications for decades, including: • offices; • c all centres; • banks; • courthouses; • libraries;

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•m ilitary facilities; and •h ealthcare environments.

In recent years, they have gained even more popularity because of the increased use of open-plan space and demountable partitions, rising densities, and sustainable design practices––all of which have a significant impact on acoustics.

The field has also changed with the introduction of new sound masking systems. Users are no longer limited to a choice between centralized (Figure 1, page 7) and decentralized products (Figure 2, page 7), but can now select a digital or networked technology (Figure 3, page 8). However, what often gets lost in the shuffle are the key design and performance features that can have a substantial impact on the outcome within each space.

The specification gap Sound masking is a critical design choice for which one does not want to leave a lot of room for interpretation. After all, when purchasing a system, the user is not seeking the mere pleasure of owning the equipment. Without a set of performance standards, poor procurement decisions can be made. The desired level of speech privacy, noise control, and occupant comfort may be sacrificed, as well as the user’s ability to easily and cost-effectively adjust the system in the future.

To keep the focus on design and performance, the manner in which sound masking systems are specified must be updated.

They are often specified according to the aforementioned

Key performance criteria A sound masking system’s performance is determined by the following criteria: • a djustment zone size; •m asking sound generation; •v olume adjustment capabilities; • f requency adjustment capabilities; • l oudspeaker requirements; and •m easured results.

These six elements are vital to every project’s success. Clear requirements can be set for each one, in addition to various masking technologies that can meet those standards. In other words, a specification focusing on these elements allows competitive bids and, providing the terms of the specification are upheld, also ensures a high performance level from the system selected.

Adjustment zone size Acoustic conditions and user needs vary between private offices, meeting rooms, corridors, and reception areas, as well as across open-plan spaces (Figure 4, page 8). Sound masking designs with small adjustment zones (i.e. individually controllable groups of loudspeakers) enable the user to adjust the frequency and volume to meet these diverse needs.

Conversely, any designs using large adjustment zones––ranging from eight to hundreds of loudspeakers––require the

Figure 1 Images courtesy K.R. Moeller Associates Ltd.

types, limiting the number of vendors that can bid on a given project. Bidding opportunities are further restricted when the specification incorporates propriety elements such as the dimensions of components, types of inputs/outputs, and other minor details. At the other end of this spectrum are specifications that merely state “provide a sound masking system.” When compared to the manner in which most other building systems such as HVAC or fire alarms are specified, the contrast is striking.

The best practice approach for sound masking is to write a performancebased specification focusing on the qualities that are critical to the system’s effectiveness and occupant comfort.

A centralized masking system features a centrally located rack of equipment used for sound generation, volume, and frequency adjustment. This equipment is connected to a set of loudspeakers that all reproduce the centrally generated sound.

Figure 2

A decentralized masking system features master and satellite loudspeakers. The former includes the electronics for sound generation, volume, and frequency adjustment. Local changes are made by physically accessing the controls on each master, while global volume adjustments and timer functions are centrally controlled.

user to make compromises that increase the system’s effectiveness in some areas while diminishing occupant comfort in others, or vice versa (Figure 5, page 9).

The impact of these compromises is far from minimal. A few decibels of variation in masking volume can dramatically impact the system’s effectiveness, even without taking into consideration the consistency of frequency levels. In many situations, users can expect a 10 per cent reduction in performance for each decibel variation below the target masking volume. A poorly designed

system can allow as much as a 6-dB variation (i.e. ±3 dB), meaning the system’s effectiveness will be halved in some areas of the user’s space.

Zone size also affects the ease with which the user can make changes to the system in the future. Churn rates and renovations require systems that can be quickly, easily, and cost-effectively readjusted. Large zones limit the user’s ability to reconfigure the sound masking system without first physically changing its design, moving loudspeakers, or rewiring parts of the system.

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Figure 4

Image © iStockphoto.com/Peter Willems

Figure 3

A networked masking system consists of networkable components, loudspeakers, and a central method of control such as a small panel or software application. All local and global changes, including those to zoning, are made from the central location.

In other words, the most important factor within a sound masking specification is to place an upper limit on adjustment zone size. In this case, less truly is more––one to four loudspeakers in each zone provide a high degree of flexibility.

Masking sound generation Each small adjustment zone should have a dedicated masking sound generator to avoid a phenomenon called phasing (i.e. uncontrollable variations in masking levels), which occurs when numerous speakers adjacent to each other emit the same masking signal.

To maximize unobtrusiveness, each generator should also provide a sound that occupants perceive as being random (i.e. with no noticeable repeat cycle). The sound produced by the generator must cover the entire masking spectrum of 100 to 8000 Hz––frequency output beyond this range is unnecessary.

Volume adjustment capabilities The masking sound is greatly affected by the overall workplace design, including the materials used, furnishings, location on the floor, and items above the ceiling. These elements have an impact no matter how the loudspeakers are installed (e.g. upward-facing above a suspended ceiling or direct-facing cut through a ceiling). For this reason, ASTM E 1573-09, Standard Test Method for Evaluating Masking Sound in Open Offices Using A-weighted and One-third Octave Band Sound Pressure Levels, requires measurements to be taken in areas representative of all workspace types.

If the adjustment zones are large, numerous loudspeakers are set to the same output level, but after interacting with

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Acoustic conditions and user needs vary across each facility, including open-plan spaces. Small zones allow the system to be tuned to provide a consistent masking sound, speech privacy, and noise control across the entire installation.

the variables in the space as noted above, the masking volume fluctuates. Variations of 2 dB or more call attention to the masking sound, reveal its source to occupants, and diminish results.

Large-zoned designs attempt to mitigate these volume variations by including audio transformers as volume controls on each loudspeaker. However, they only provide rough adjustments of 3 dB each. When the volume cannot be finely adjusted in small areas, users need to set a volume that is best ‘on average,’ compromising comfort or effectiveness at various, unpredictable points across their space.

The specification should call for fine volume controls for each small zone. Increments of 0.5 or even 1 dB enable the user to adjust the sound whenever needed in order to accommodate variable acoustic conditions. The specification should also require the final masking volume be consistent within a range of 1 to 1.5 dB in all areas desired. Again, the benefits are consistent performance and comfort.

Frequency adjustment capabilities The sound masking system should also provide fine frequency control within each small adjustment zone.

Image courtesy K.R. Moeller Associates Ltd.

Figure 5

The most important factor is to place an upper limit on zone size. Small zones of one to four loudspeakers provide a high degree of flexibility. Larger zones require compromises to be made between comfort and effectiveness. As the diagram shows, the larger the zone, the more people affected by those compromises.

The range of masking sound is generally specified to be between 100 to 8000 Hz. The system should provide control over these frequencies via third-octave adjustment because it is both the industry standard and the basis for masking targets that are set by acousticians.

However, providing third-octave adjustment is not enough when these controls are paired to large adjustment zones. A well-designed system provides equalization for each group of one to four loudspeakers.

Loudspeaker requirements As long as the masking system can meet the volume and frequency targets established by the specification, it is not essential to specify the loudspeaker’s size, wattage rating, or other parameters. Yet, it is worth noting very small loudspeaker drivers (i.e. less than 76 mm [3 in.]) are unlikely to generate sufficient levels below several hundred hertz (i.e. down to the required 100 Hz). These low frequencies are necessary to create the full masking spectrum. While they play a relatively minor role in reducing speech intelligibility, they are vital to occupant comfort. Most masking loudspeakers are 102 to 203 mm (4 to 8 in.) in diameter and rated from 10 to 25 watts.

Measured results The true gauge of whether the sound masking system ultimately selected is performing as required is gained from post-adjustment measurements.

The specification should require specific results that are measured and documented. Best practice is to require a test in each 93-m2 (1000-sf) area, and have the vendor adjust the sound masking system within that area as needs dictate. (Some systems may be able to outperform this requirement, but it is a good baseline.)

Two or three types of measurements should be required: 1.

Overall volume and variation tolerances—masking volumes tend to range between 42 and 48 dB, depending on the type of space and the user’s performance requirements.

As previously mentioned, the results should be consistent within a range of 1 to 1.5 dB or less.

2.

Masking frequency curve––there is a general curve the acoustical community considers effective and comfortable. It is defined in thirdoctave bands. The specification should set maximum variations for each frequency band; ± 2 dB variation is a reasonable expectation.

3.

Temporal uniformity––this refers to the consistency of the masking volume over time. While this attribute can be assessed, it is usually not an issue and is less frequently specified and evaluated.

It is important to remember there are no independent standards for masking performance, only standards relating to measurement such as ASTM E1573-09. A specification stating the sound masking system is or should be ‘compliant’ with any ASTM standard is misleading. Instead, it is essential that it outlines all the above requirements for masking output.

Additional considerations Depending on their significance to the project at hand, some secondary characteristics may also need to be included in the specification, including: • t imer functions; • z oning and control methods; • s ecurity features; •p aging functions; • esthetics; • certification; •d rawings; and • c ompliance form.

Timer functions Timers automatically adjust the masking volume to vary in anticipation of noise levels throughout the day, balancing effectiveness and comfort. For example, the user may want a lower masking volume at a certain time when there are fewer occupants in the facility.

Considerations may include: • whether the timer provides variable rates of volume change; • number of independent timer zones; • whether the daily schedules can be independent; and • if unique schedules can be programmed for specific days of the year (e.g. holidays and special events).

Masking systems may also offer a rampup feature. It is best to specify this in retrofit situations because it is used to

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Photo © iStockphoto.com/Yvan Dubé

Figure 6

Sound masking consists of a series of loudspeakers installed in a grid-like pattern in or above the ceiling, and a method of controlling their output.

gradually introduce the masking sound, allowing occupants to easily acclimatize to the change in their acoustical conditions.

Zoning methods Beyond masking zones, most systems can be zoned for various functions, including paging and timer functions, as well as local occupant control (e.g. in a meeting room). In this case, the type of zoning is relevant. For example, hardwired zones require advanced planning because a contractor will have to re-cable parts of the system when future changes need to be made. Digital zones can usually be re-assigned without altering the system’s physical design. Less planning is required from the outset because any changes can be made in minutes.

Control methods The method of controlling the system impacts the ease, cost, precision, and amount of disruption associated with making initial and future adjustments. Some designs provide central control over a limited range of features. Others provide central control over a few features and local control over others. There are also designs offering control over all features from a central location.

Most users make significant changes to their space over time–– to department location, demountable partition placement, or furniture system configuration––and it is important to consider how the corresponding changes will be made to the sound masking system. The specification can include the types of features and settings that need to be controlled and from what kind of access point (e.g. hardware and/or software).

Security features Depending on the user, security may be another key consideration. In this case, the specification should describe both the physical and electronic security features for the sound masking system.

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Drawings can help identify differences between masking proposals because they show the components, quantities, and locations, making it easier to spot design shortcuts and discuss them with the vendor.

Physical features can include housing below-ceiling equipment in locked enclosures and also ensuring enclosed rather than exposed cabling connections. Electronic measures can include monitoring, password-controlled access, and encrypted communication.

If security is a concern, additional masking generators and longer generation cycles are better because short cycles can easily be filtered out of recorded conversations.

Paging functions Many sound masking systems can provide simultaneous overhead paging and background music functions. If the user requires these features, they should be covered in the specification.

Esthetics When installed in an open ceiling, the system’s appearance should be considered, including the look of the loudspeakers (e.g. an industrial esthetic or similar to a lighting pendant), the cable and cable connections, as well as the loudspeaker suspension methods (e.g. chain or a braided steel cable).

Certifications Another important aspect of the specification concerns the system’s certifications. Though not critical to performance per se, they are essential to meeting regulatory requirements.

Sound masking systems must meet Underwriters Laboratories (UL) or similar standards for electrical safety. Any components installed in air-handling plenum or via cut-throughs in a suspended ceiling must also be tested to meet UL 2043, Standard for Safety Fire Test for Heat and Visible Smoke Release for Discrete Products and their Accessories Installed in Air-handling Spaces.

Cables must be plenum-rated. If using low-voltage power supplies, these should conform to UL 1310, Class 2 Power Units, to avoid conduit requirements. Digital masking systems need to meet the electromagnetic interference (EMI) standards.

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Photo © iStockphoto.com/Steve Cole

Figure 7

A well-constructed specification is essential to ensuring the masking system provides an effective and comfortable environment for all employees, increasing productivity.

As long as the loudspeaker can meet the volume and frequency targets, it is not essential to specify other parameters, except in open ceilings where esthetics matter.

If sustainability is a goal within the space, users might also voluntarily require compliance with the European Restriction of Hazardous Substances (RoHS) directive, which limits the quantities of certain materials used in the system’s components.

Drawings Even if the sound masking technology the vendor proposes adheres to a generally worded design guide, the vendor may intend to implement it in a different manner. Therefore, it is important whenever possible, to require drawings as part of the bid submission process (Figure 6, page 10).

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These documents can help identify differences between sound masking proposals because they show the components, quantities, and locations, making it easier to spot design shortcuts and subsequently discuss those deviations with the vendor.

Ideally, of course, the drawings should be included as part of the specification itself, allowing the user to set the adjustment zones for each area. For example, there may be areas where the client wishes to use zones smaller than the four-loudspeaker maximum, such as in private offices and meeting rooms. These drawing should be created by the user in conjunction with an acoustical consultant or trusted vendor.

Compliance form Another useful document to request in the specification is a compliance form. Vendors should be asked to submit a statement indicating their adherence to each aspect of the specification. They should also be required to note any deviations, describing how their system’s design differs.

Own the spec Acoustics are an integral part of a project’s long-term success and should be planned from the outset. While every sound masking system introduces a sound into the space, overall performance can vary dramatically. A well-constructed specification is essential to ensure the technology and the system’s design meets the user’s current and future requirements (Figure 7). If not, the sound masking system may be ineffectual, underused, or become a source of irritation itself and possibly turned off.

However, even with a well-written specification, the user could end up with a non-conforming system unless the specifier, user, or another person involved in the design and procurement process is appointed as a guardian whose responsibility it is to ensure bids meet the criteria outlined.

Many times the value of a well-designed specification is nullified because no one is asked to ensure all proposals–– and, indeed, the system ultimately selected––conform to the desired performance levels.

It is also wise to learn what services are offered in conjunction with each proposal under consideration. The sound masking system should be supported by professionals who can properly design and implement it and provide the user with ongoing support.

Notes 1 For a sample of a performance-based specification online, visit www.soundmaskingspecs.com.

Strategies for Sound Masking Part Two Providing acoustic comfort with sound masking

BY NIKLAS MOELLER, MBA

Niklas Moeller, MBA, is vice-president of K.R. Moeller Associates Ltd. (Burlington, Ont.), a global developer and manufacturer of sound masking systems for more than 30 years. He has been in the sound masking business since 1998.

Moeller writes an acoustics blog at soundmaskingblog.com.

He can be reached via e-mail at nmoeller@logison.com.

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All images courtesy K.R. Moeller Associates Ltd.

Tuning Out Noise Providing acoustic comfort with sound masking

By Niklas Moeller

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pen-plan space, modular walls, and reflective surfaces such as glass, concrete, and metal are just a few of the design trends making today’s interiors even more dependent on sound masking for speech privacy and noise control. Since a sound masking system’s ability to provide these benefits largely depends on meeting the specified spectrum—or ‘curve’—throughout the facility, post-installation tuning is an essential part of the commissioning process. When handled poorly (or skipped altogether), the tuning of sound masking can greatly affect speech intelligibility, as well as occupants’ concentration and their overall workplace satisfaction.

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The curve defines what the sound masking system’s measured output should be within the facility where it is installed. This target should be set by the client’s acoustician or a third party such as the National Research Council (NRC), rather than by the sound masking system’s manufacturer or vendor.

The typical range is between 100 to 5000 hertz (Hz), but can go as high as 10,000 Hz. Unlike white or pink noise—terms often mistakenly substituted for ‘sound masking’—the volume of these frequencies follows a non-linear curve specifically engineered to balance acoustic control and occupant comfort.1 Successful sound masking implementation involves achieving both goals in equal measure.

Regardless of how the sound masking system has been designed (i.e. the out-of-the-box settings, placement, and orientation of loudspeakers), the sound it distributes changes across the facility as it interacts with various interior elements, such as the layout and furnishings. To meet the specified curve, the client’s acoustician or the sound masking vendor’s technician must adjust the system’s volume and frequency settings. In other words, the masking sound has to be tuned for the particular environment in which it is installed.

This process should occur after the ceilings and furnishings are in place, and with mechanical systems operating at daytime levels. As activity and conversation prevent accurate measurement, it should also be done before the facility is occupied or after hours. The exact method will vary by product, but generally the acoustician or technician uses a sound level meter to measure the masking sound at ear height (i.e. the level at which occupants experience its effects), analyzes the results, and adjusts the volume and frequency settings accordingly. He or she repeats these steps until the curve is met at each tuning location.

Understanding tolerance Some degree of variation from the curve is expected because it is impossible to achieve perfection in every tuning location. However, variations have an impact on the masking sound’s performance and can draw occupants’ attention to it. For that reason, the specified curve is usually accompanied by a ‘tolerance’ limiting the amount by which the sound is permitted to deviate from the goal across the client’s space.

Historically, this value was often set to ±2 dBA (i.e. plus or minus two A-weighted decibels), giving an overall range of 4 dBA—however, such wide swings in volume have a profound impact on speech intelligibility. Site tests are required for absolute Articulation Index (AI) or comprehension levels, but one can generally state each decibel decrease in overall masking volume reduces performance by 10 per cent.2 Therefore, a tolerance of ±2 dBA can allow occupants to understand up to 40 per cent more of a conversation in some areas than they can in others.

Specifications allowing ±2 dBA or even ±3 dBA are still in circulation, but they are a remnant of the capability of legacy technologies. When

A sound masking spectrum or ‘curve’ should be specified by an acoustician or supplied by an independent third party like the National Research Council (NRC).

properly designed and tuned, newer sound masking systems can achieve ±0.5 dBA, giving an overall range of 1 dBA. The role of masking architecture The importance of achieving tight tuning tolerances throughout a sound masking installation is emphasized by how the ‘architecture’ used by this technology has evolved since first introduced in the 1960s. To improve both the accuracy of the tuning process and the efficiency with which it is done, industry engineers have sought to reduce zone size (i.e. individually controllable groups of loudspeakers) and devise new control methods.

Centralized sound masking The earliest sound masking systems used a centralized architecture. In this configuration, the electronic equipment for generating and amplifying the masking sound, as well as providing volume and frequency control, are located within an equipment room or closet. The settings established at this central point are broadcast over SOUND MASKING | Construction Canada E-BOOK

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a large number of loudspeakers. A global frequency control is provided for each of these large zones.

Though most offer analog volume control at each loudspeaker within a large zone, it is limited to four to five settings, typically in 3-dBA steps.

Since acousticians or technicians cannot make precise volume changes in specific areas, they have to set each large zone to a level that is best on average.

Due to variations in the acoustic conditions across the space and the impact of interior elements, the masking sound is too low in some areas and too high in others. If they raise the volume to address a performance deficiency in one area, the sheer size of the zone means they simultaneously increase it in others, reducing occupant comfort, or vice versa. This pattern repeats at unpredictable points across the facility, which is why centralized system specifications typically set tolerance to ±2 to 3 dBA, giving an overall range of 4 to 6 dBA.

A centralized architecture uses centrally located equipment for sound generation, volume, and frequency adjustment. This equipment is connected to a large number of loudspeakers—as few as eight, or as many as hundreds—forming a single zone.

A decentralized architecture uses ‘master’ loudspeakers for sound generation, volume, and contour control. Each master is connected to up to two ‘satellites’ that repeat its settings, making zones one to three loudspeakers in size. Local adjustments are made using a screwdriver or remote control.

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Decentralized sound masking Decentralized architecture emerged in the mid1970s to address a major deficiency in the ability to tune centralized systems—large zone size.

Rather than locating sound generation, volume, and frequency control in a central location, the electronics required for these functions are integrated into ‘master’ loudspeakers, which are distributed throughout the facility—hence the ‘decentralized’ name.

Each ‘master’ connects up to two ‘satellite’ loudspeakers, which repeat their settings.

Therefore, a decentralized system’s zones are only one to three loudspeakers in size (i.e. 20 to 62 m2 [225 to 675 sf]). As each small zone offers fine volume control, local variations can be addressed, allowing more consistent and effective masking levels across a facility. However, there are still limits to the adjustments with respect to frequency.

Further, the technician must enter the ceiling to make changes directly at each ‘master’ loudspeaker, using either a screwdriver (i.e. with analog controls) or an infrared remote (i.e. with digital controls), making adjustments time-consuming.

It is advisable to measure performance and modify a sound masking system’s settings when changes are made to the physical characteristics of the space (e.g. furnishings, partitions, ceiling, flooring) or to occupancy (e.g. relocating a call centre or human

resource functions into an area formerly occupied by accounting staff). The likelihood these types of change will occur during a sound masking system’s 10- to 20-year lifespan is almost certain, so one simply cannot take a ‘set-it-and-forget-it’ approach.

Sound masking engineers needed to develop a more practical way of adjusting the sound.

Moving sound generation, as well as control over volume and frequency, into small zones addresses the tuning challenges that are posed by large ones.

Rather than requiring numerous occupants to make compromises between the masking sound’s effectiveness and their comfort, technicians can adjust the sound according to local conditions.

A networked architecture uses ‘hubs’ to house the electronics required for sound generation, volume, and frequency control.

Zones are one to three loudspeakers in size. Local adjustments and global changes are made from a small control panel or software application.

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Networked sound masking The first networked sound masking system was introduced a little over a decade ago. This technology leverages the benefits of decentralized electronics, but networks the system’s components together throughout the facility—or across multiple facilities—to provide centralized control of all functions via a control panel and/or software.

Zoning (i.e. for paging, timer functions, and inroom occupant control) is also digital rather than hardwired. Therefore, changes can quickly be made following renovations or moving furniture or personnel, maintaining masking performance within the space without disrupting operations.

When designed with small zones of one to three loudspeakers offering fine volume (i.e. 0.5 dBA) and frequency (i.e. 1/3 octave) control, networked architecture can provide consistency in the overall masking volume not exceeding ±0.5 dBA, as well as highly consistent masking spectrums, yielding much better tuning results than possible with previous architectures. For improved efficiency, some networked sound masking systems can also be automatically tuned using a computer, which first measures the sound and then rapidly adjusts the masking output to match the specified curve.

Guidelines and reporting Due to these advancements in the field of sound masking and the essential role it plays in achieving effective acoustics in today’s facilities, ASTM Subcommittee E33.02 on Speech Privacy— part of ASTM Committee E33 on Building and Environmental Acoustics—is currently working to update the related performance standards through WK47433, Performance Specification of Electronic Sound Masking When Used in Building Spaces.

The group is also in the process of updating: ● ASTM E1130, Test Method for Objective Measurement of Speech Privacy in Open Plan Spaces Using Articulation Index;

Tuning can be a time-consuming process, but it is essential if the client is to derive the full benefit from their investment in sound masking technology.

This illustration shows the placement of sound masking loudspeakers (i.e. the grey dots) regardless of which type of architecture is used to form the zones.

● ASTM E1374, Guide for Open Office Acoustics and Applicable ASTM Standards; ● ASTM E1573, Test Method for Evaluating Masking Sound in Open Offices Using A-weighted and One-third Octave Band Sound Pressure Levels; and ● ASTM E2638, Test Method for Objective Measurement of the Speech Privacy Provided by a Closed Room.

In the meantime, a minimum-performance guideline involves requiring the masking sound be measured in each 90-m2 (1000-sf) open area and each closed room, at a height between 1.2 to 1.4 m (4 to 4.7 ft) from the floor (i.e. at ear height rather than directly below a loudspeaker), and adjusted within that area as needs dictate. Some systems can adjust for smaller areas, but this is an acceptable baseline.

This illustration shows the number of zones provided by a centralized architecture. It assigns areas to zones based on simple categories, such as open plan, closed room, corridor, and reception, based on the assumption that they have the same or very similar acoustic characteristics. Note that the volume and equalization settings for Zone 1 (highlighted in yellow) are applied to three different areas within the facility, encompassing seven private offices, three bathrooms, a boardroom, a waiting area, and a mixed-use room.

Masking volume is typically set to between 40 and 48 dBA, and the results should be consistent within a range of ±0.5 dBA or less. The curve should be defined in third-octave bands and range from 100 to 5000 Hz (or even reaching as high as 10,000 Hz). Having ±2 dB variation in each frequency band—this tolerance is different from that set for volume—is a reasonable expectation.

The technician should adjust the masking sound within that area as needs dictate and SOUND MASKING | Construction Canada E-BOOK

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Sound Masking and Wall Construction

A

sound masking system’s role is to control the acoustic conditions throughout a facility in the same way as temperature and lighting. One does not want cold or dark areas and, similarly, one should strive to achieve a consistent acoustic environment—not have a low ambient volume in one area and an effective one in others.

Intentionally omitting sound masking from particular areas runs contrary to the goal of ensuring this technology is as effective and unobtrusive as possible. Occupants will walk in and out of treated areas that differ in ambient volume (sometimes by as much as 10 to 12 dBA), calling their attention to the sound and, if the loudspeakers are visible, also reveal its source. The same can be said of attempting to spot-treat an area where a more obvious acoustical issue exists, such as within an open plan or outside a boardroom.

However, many people continue to exclude sound masking from private offices and meeting rooms, primarily in the belief closed spaces are afforded sufficient speech privacy and noise control via physical isolation.

Modern construction does not always allow for a high level of physical containment. To preserve flexibility, walls are often built to below the suspended ceiling or using demountable partitions, and may be largely composed of glass. Construction budgets can also limit wall options. In any case, even if walls are built deckto-deck, voices find their way from one room to another through a variety of pathways. An open door is the biggest Achilles’ heel, but other common channels include passing through the plenum, return air grilles, and ductwork, gaps along the window mullions, ceiling, and floor—and even the walls themselves.

In order to use floor-to-ceiling walls with lower sound transmission class (STC) ratings and still achieve the acoustic control occupants expect in closed rooms, it is best to include sound masking in their design. If a wall decreases the intrusion of voice into the room by a decibel, then the signal-to-noise ratio (SNR) drops by a decibel.

An identical drop occurs when the masking volume is raised by one decibel. Sound masking typically adds 5 to 12 dBA of ambient volume to closed rooms, which is why one sometimes hears that sound masking ‘adds 10 STC points’ to walls.

Budget-wise, the sound masking may represent $10 to $20/m2 ($1 to $2/sf) of space, but it offsets much more than that in terms of construction above the ceiling. The ability to provide private rooms with walls to the ceiling also increases the ease and costeffectiveness of relocating them to suit future needs.

An exception to this guideline might be a large training room, where speech intelligibility is vital and, therefore, sound masking is omitted. Such rooms should be well-isolated using deck-to-deck construction with higher STC walls.

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This illustration shows the number of zones provided by a decentralized or networked architecture within the same facility. Whereas the centralized architecture only offers three zones, this design features 44 zones, allowing the technician to adjust the masking sound according to local conditions in order to meet the specified curve across the entire treated space.

provide the client with a detailed final report demonstrating the desired curve is consistently provided throughout the space. If there are any areas where the masking sound is outside the tolerance, this document should clearly identify the location and reason (e.g. noise from mechanical equipment or HVAC).

Tuning can be a time-consuming process, but it is essential if the client is to derive the full benefit from their investment in sound masking technology. In this way, they can be confident the system is providing the intended effects and they are equally enjoyed by all occupants across their facility.

Notes 1 For a deeper exploration of the ‘colours’ of noise, see this author’s article, “If You Need Sound Masking, Ask for it By Name,” for Construction Canada Online. Visit www.constructioncanada.net/if-youneed-sound-masking-ask-for-it-by-name.

2 For more, see this author’s article, “Exploring the Impacts of Consistency in Sound Masking,” in a 2014 issue of Canadian Acoustics (vol. 42, no. 3), the journal of the Canadian Acoustical Association.

Strategies for Sound Masking Part Three Understanding acoustic privacy within the built environment

BY NIKLAS MOELLER, MBA

Niklas Moeller, MBA, is vice-president of K.R. Moeller Associates Ltd. (Burlington, Ont.), a global developer and manufacturer of sound masking systems for more than 30 years. He has been in the sound masking business since 1998.

Moeller writes an acoustics blog at soundmaskingblog.com.

He can be reached via e-mail at nmoeller@logison.com.

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CONFIDENTIAL

Photo © iStockphoto.com/mediaphotos

CORPORATE

Understanding acoustic privacy within the built environment

By Niklas Moeller

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yping the word ‘privacy’ into any search engine yields a virtually endless stream of entries describing the ways in which it can be violated.

There are reports of hackers acquiring credit card information, law enforcement agencies mining social networking sites, and members of the public using drones to take aerial photographs. More recent headlines indicate voice-activated televisions can even eavesdrop on owners.

The preoccupation with vulnerabilities exposed by the Internet and electronic products is understandable given their relatively rapid spread into almost every aspect of everyday life. However, privacy can still be violated in ‘traditional’ ways. In fact, it can even be lost to those who do not intend to infringe upon it.

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People are often exposed to sensitive information simply by being within audible range of a conversation.

Current privacy legislation tends to focus on securing access to information stored on computers or within filing cabinets, but attention also needs to be paid to the built environment. When examined in this context, privacy has both an acoustic and a visual component. (This article primarily focuses on the former, except insofar as it is affected by the latter.)

What is acoustic privacy?

Many people immediately equate acoustic privacy with speech privacy, but there is more to this concept than the ability to clearly hear what another person is saying.

Where is it needed?

A lack of acoustic privacy carries real risk, particularly in facilities where there is a perceived need for it or an expectation on the part of its users. Examples include hospitals, bank branches, law offices, government, and military facilities. However, other types of spaces—such as commercial offices, call centres, and hotels— have privacy needs as well. The degree required typically depends on the type of activities the space hosts.

Why is it needed?

It is easy to understand the need for acoustic privacy—or even acoustic security—from a speaker’s perspective, particularly within environments where medical information, financial planning, personal relationships, trade secrets, or matters of national security are being discussed. However, a lack of acoustic privacy can have impacts beyond divulging sensitive information to unintended parties. This fact

Photo © iStockphoto.com/fotostorm

For example, if the conversation taking place in a room next to an occupant is unintelligible, one may still be able to identify the speaker’s tone and determine whether they are happy, sad, or angry. This type of information can be considered private under certain circumstances, such as when coming from behind the closed door of a human resources manager’s office— the same can be said for non-verbal noises like those overheard from an adjacent hotel room.

How much of a conversation is understood also depends on whether or not the speaker can be seen. This effect—known as visual cues—has been quantified by various studies.1 Generally speaking, if one can only understand 20 per cent of someone’s conversation when not looking at them, the ability to see their lips increases that amount to nearly 55 per cent. If you start at 50 per cent, visual cues increase it to almost 90.

In other words, there is also a visual component to acoustic privacy, which is important to bear in mind when designing a space.

Further, acoustic privacy should not only be considered from the speaker’s perspective, but also that of the listeners. The reasons will become clear as this article explores the various impacts of a lack of privacy.

When people can unintentionally overhear a conversation, they often feel annoyed or even the sensation their own privacy is being violated. It can also make one insecure about the level of speech privacy, compromising an ability to freely communicate.

becomes clear when perspective shifts from the person talking to the involuntary listener.

When a noise or voice enters an occupant’s ‘space,’ some degree of annoyance is typical, but it can also make one feel as though one’s privacy—or sense of physical separation—is being invaded. Perhaps the most relatable examples of this sensation are when the guest in a neighbouring hotel room turns up the television’s volume or the patient at the other end of a waiting area starts speaking loudly into his or her cell phone.

If conversations can be inadvertently overheard, occupants can also become self-conscious about their own level of privacy. In some contexts, it can create a sense of unease, which in turn impacts the ability to freely communicate. For instance, if a patient can hear what is happening in the adjacent examination room at a medical clinic, he or she might be less inclined to SOUND MASKING | Construction Canada E-BOOK

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Photo © iStockphoto.com/russelltatedotcom

at University of California, Berkeley, found lack of speech privacy is the top complaint in offices.2 Participants expressed irritation at being able to overhear in-person and telephone communications, as well as concern for their own level of privacy.

Voices cause vibrations in windows, doors, pipes, and walls, which can be picked up by audio surveillance equipment and translated into intelligible speech. Sound masking can be applied to these structures in order to help protect privacy.

disclose information to the nurse or doctor, out of fear of being overheard.

The degree of acoustic privacy afforded by the built environment can even impact an organization’s brand image. People want to be in control of personal information when meeting with a financial or legal advisor, for example, and a positive acoustic experience can reinforce confidence in a firm. This level of protection is also indispensable for staff to effectively negotiate the terms of various agreements.

In some countries, the protection of verbal communication within particular types of facilities is actually mandated by law. The Health Insurance Portability and Accountability Act (HIPAA) introduced by the U.S. Department of Health and Human Services in 1996 is a good example.

It requires healthcare entities to take “reasonable safeguards” to ensure there is speech privacy during both in-person and telephone conversations with patients and between employees.

Acoustic privacy is also vital to employees’ overall satisfaction with their workplace. A worldwide, decade-long survey of more than 65,000 people run by the Center for the Built Environment (CBE)

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What about the open plan?

The topic of workplace satisfaction also emphasizes the need to consider those occupying spaces other than closed rooms. Though some may dismiss the importance of acoustic privacy when designing an open plan, studies show it has a significant impact on productivity.

For instance, research conducted by Finland’s Institute of Occupational Health shows unwilling listeners demonstrate a five to 10 per cent decline in performance when undertaking tasks such as reading, writing, and other forms of creative work.

Simply hearing someone is speaking can disturb concentration, but this problem is greatly magnified when one can clearly understand what is being said because, if a conversation can be followed, it is much harder to ignore it.

Though an organization might not consider privacy a goal within an open plan, it is impossible to justify increasing disruptions. Taking the steps required to lower speech intelligibility within this type of space increases occupants’ output and reduces error rates.

Assessing speech intelligibility The subject of speech intelligibility cannot be discussed without getting into the concept of degrees because every word of a conversation does not need to be understood for privacy to be violated. Due to the redundancies and patterns in speech, building occupants can follow much of what is said even if only half of it is overheard— particularly if they have previously been part of a similar conversation. Further, private details can be exposed even when a small part of the discussion is overheard.

Further, it is difficult to subjectively assess degrees of speech intelligibility. For example, a listener would have a hard time indicating with any precision whether they can understand 40, 55, or 70 per cent of what someone else is saying.

Fortunately, there are ways to measure and quantify the degree of privacy afforded by the built

Figure 1

Images courtesy K.R. Moeller Associates Ltd.

environment. The Articulation Index (AI) remains the most widely used method. It was developed at Bell Labs in 1921 by Harvey Fletcher as he sought to quantify speech comprehension over telephone lines. During the 1950s, those that were involved in the speech privacy sciences adopted his invention as a measure of exactly the opposite: how much one could not understand.

To calculate AI, one uses a test signal including the frequencies known to specifically impact speech comprehension. This signal is measured at 1 m (3.2 ft) from the ‘source’ and again at the ‘listener’ location.

The background sound level is also measured at the ‘listener’ location in order to quantify how loud the test signal is relative to it—a value known as the signal-to-noise ratio (SNR). This value is critical, because the lower the SNR, the less the intelligibility and the greater the speech privacy.

For AI, SNR is measured in each of 15 frequency ranges (from 200 to 5000 Hz). Each of these ranges is weighted according to the degree to which it contributes to speech comprehension. The final AI value ranges from 0 (where conversation is completely unintelligible) to 1 (where everything is heard and understood). The human voice varies from person to person, depending on factors such as sex and age.

AI ratings are challenging to interpret in a meaningful way, so studies have been done to correlate them to subjective ‘privacy’ categories.

However, the value of these groupings is somewhat diluted by the wide range of comprehension within each one: • ‘ confidential’ privacy ranges from 0 to 0.1; • ‘ ‘normal’ from 0.1 to 0.2; and • ‘ ‘marginal’ from 0.2 to 0.3.

If AI is above 0.3, there is effectively no privacy.

As shown in Figure 1, the relationship between AI and actual comprehension is not linear. On a 0 to 1.0 scale, many would expect a value of 0.5 to mean listeners would understand 50 per cent of a conversation, but—as is clear from the graph—they would actually understand approximately 95 per cent. The shaded areas along the left of the graph show the confidential, normal, and marginal privacy ranges, indicating just how low an AI is required for true privacy.

A more recent arrival on the acoustical scene is a metric called the Privacy Index (PI). PI is based on

The relationship between Articulation Index (AI) and intelligibility is not linear—for example, a value of 0.5 means a listener can understand approximately 95 per cent of a conversation, not 50 per cent. A very low AI value is, therefore, required for true privacy.

AI, in that it is calculated as 1.0 minus the AI value, multiplied by 100, and expressed as a percentage; in other words: 1–AI x 100 = PI (%)

However, PI can be misleading. Part of the problem likely stems from its use of the word ‘privacy,’ which can cause users to come to the wrong conclusion about the rating’s meaning. The fact it is expressed as a percentage creates even more potential for confusion. For example, with an AI of 0.3, there is a PI of 70 per cent.

Figure 1 demonstrates the reason to avoid this metric. When told the PI is 70 per cent, most would assume they would only understand 30 per cent of what is being said. In reality, nearly 85 per cent would be understood. Thus, building professionals should be cautious when investigating acoustical solutions and interpreting related PI statements.

How sound travels To design the built environment for acoustic privacy, it is also important to understand the three ways sound (e.g. voice) travels to a listener.

Sound follows a direct path when it travels uninterrupted from the source to the listener or penetrates a barrier between them, such as a wall.

This transmission path contributes the most to SOUND MASKING | Construction Canada E-BOOK

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Figure 2

furnishings. Finally, it should be noted that sound can travel in a diffracted path—that is, it can bend around obstacles. This pathway is generally less significant than the first two.

Since speech travels in these various ways, it can be difficult to contain. Several methods must be employed because no single technique can sufficiently address all transmission pathways.

As depicted above, he area of intelligibility around a speaker is not circular.

Its shape is determined by numerous factors, including the orientation of the person speaking, as well as the physical barriers and absorptive/reflective materials that are used within the space.

Figure 3

When sound masking is applied, the area of intelligibility shrinks.

high levels of speech reaching the listener. In this context, high levels refer to more intelligible words at a relatively high volume. However, it can also travel on a reflected path. This type of transmission occurs when sound bounces off the various surfaces within the space, such as floors, ceilings, walls, and

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Designing for acoustic privacy Of course, the louder a person speaks, the more likely he or she is to be heard. Building occupants should always try to be mindful of their voice level, but proper etiquette is only effective to a point. The remainder of the acoustical burden has to be borne by the design using a three-tiered approach called the ‘ABC Rule,’ which stands for absorb, block, and cover. Acoustic privacy is achieved by using a welldesigned combination of these tactics. (The brief outline in this article touches on the interior fit-out and furnishings, not the shell of a building.)

Absorb The ‘A’ in ‘ABC’ stands for adding absorption. As speech sounds hit various surfaces within a facility, they are reflected back into the space. If those surfaces comprise hard materials such as concrete, glass, and metal, the reflected sound energy remains high and the overall volumes will rise.

A high percentage of hard surfaces also increases reverberation (i.e. echo) within the space, making it uncomfortable. Additionally, it can lower intelligibility due to the presence of more persistent sounds in the space, often referred to as the ‘cafeteria effect.’However, it can also increase intelligibility— particularly in situations where there are not a lot of competing voices—because voice travels a longer distance and, hence, conversations can be heard from further away.

To control this type of transmission, absorptive materials must be applied to the ceiling, walls, and workstation partitions. As the ceiling is usually the largest unimpeded surface within a facility, organizations should invest in the best acoustic tiles or panels they can afford and ensure consistent coverage throughout their space.

Block The ‘B’ stands for blocking speech transmission using walls, windows, doors, and other physical

structures. This method is most obviously used in the construction of enclosed rooms, but it is also extremely useful within the open plan. If there are no barriers between occupants in these spaces, speech travels more easily and the ability to see (and be seen) further reduces privacy due to the natural capacity for lip-reading. Again, though some might argue privacy is not expected within an open plan, understandable speech disrupts occupants’ concentration. For this reason, workstation partitions should be no lower than seated head height—that is, 1524 to 1651 mm (60 to 65 in.). Even the direction in which people face will often have an effect on their voices’ volume within the neighbouring workspace. Therefore, occupants should be seated facing away from each other on either side of partitions.

Today, there are numerous pressures to reduce the height of workstations or eliminate them altogether. This trend has had a dramatic impact on the acoustical performance of open plans because though other treatments can reduce overall volume levels and deal with noises generated from farther away, they have no effect over very short distances.

When barriers are eliminated, local noise sources remain highly intelligible and disruptive.

Cover ‘C’ stands for covering, which can involve installing a sound masking system. This technology consists of a series of electronic components and loudspeakers typically installed above the suspended ceiling, which distribute a comfortable background sound throughout the facility. Though most people compare the output of a well-designed and professionally tuned masking system to that of softly blowing air, it has been specifically engineered to cover the range of frequencies in human speech. This sound also covers up incidental noises arising from general workplace activities or minimizes their disruptive impact on occupants by reducing the change between baseline and peak volume levels within the space.

The impact of background sound levels Most people are familiar with using walls, doors, workstations, and a well-planned layout to physically block voices and noises, as well as the benefits of installing ceiling tiles, wall panels, and soft flooring

to absorb them. Fewer understand the role sound masking plays in achieving acoustic privacy.

As shown in Figure 2 (page 26) the area of intelligibility around an individual is not a simple circle. Rather it is a complex shape determined by numerous factors including the speaker’s orientation, physical barriers, and absorption/reflection of the voice by the various interior finishings, furniture, and other items within the space.

In any space, voices and noises diminish in volume over distance. However, background sound levels are often so low in indoor environments speech carries intelligibly over 9 to 15 m (30 to 50 ft) or more in open space. By increasing the background sound level, sound masking reduces the signal-to-noise ratio. As shown in Figure 3 (page 26), any voices will disappear below the new level after a much shorter distance.

The exact length is, of course, a function of the space’s entire acoustic design. However, as illustrated by the AI measurements conducted between the two workstations shown in Figure 4 (page 28), sound masking plays an integral role.

This open-plan area’s acoustical design was suitably planned. The partitions are 1650 mm (65 in.) tall and perform well in terms of both absorption and isolation. The ceiling tiles are highly absorptive (i.e. 0.95 NRC). The lighting system is indirect so as to not reflect too much voice/noise back down into neighbouring work areas. A sound masking system is installed above the suspended ceiling.

Figure 5 (page 28), shows the results of the AI tests conducted between the two workstations.

Despite the high-performance acoustical design elements, speech comprehension is nearly 85 per cent when the sound masking system is off, because the existing background sound level is only 40.6 dBA. When the system is turned on, comprehension quickly declines. In fact, for each decibel of increase in masking volume, comprehension drops by an average of 10 per cent.

When adding sound masking, it is important to ensure the system is both designed and tuned so as to provide consistent coverage throughout the space. Outdated specifications might allow for a wide tolerance (e.g. up to 4 dBA), but as indicated

by Figure 6 (page 29), such variations in masking levels permit a swing of 40 per cent or more in performance. Modern, well-tuned sound masking systems are able to keep variations to just 1 dBA SOUND MASKING | Construction Canada E-BOOK

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The doorway is a challenge for a closed space. Even when closed, the it usually presents the weakest link, but when it is open, it does not matter how well the walls have been constructed, the level of sound isolation dramatically drops.

Figure 4

Articulation Index tests were conducted between these two workstations to determine how much of an impact sound masking has on speech intelligibility, even within an otherwise acoustically well-designed space.

Figure 5

The results of the AI tests show despite using absorption and blocking strategies, speech comprehension remains nearly 85 per cent until sound masking is applied. Comprehension drops by an average of 10 per cent for each decibel of increase in the masking volume.

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or less, providing dependable coverage throughout the installation.

The masking sound must be tuned to meet a sound masking spectrum or curve, which is specified by an acoustician or provided by an independent party such as the National Research Council of Canada (NRC). The specified tolerance indicates by how much the sound is allowed to deviate from that curve. The introduction of decentralized-networked technologies over the last decade has made it possible to keep variations to just ±0.5 dBA, providing a much higher level of consistency in the masking sound across a facility.

Considerations for closed rooms Maintaining an adequate background sound level is also important in closed rooms. Generally speaking, an occupant’s expectation of privacy is higher in this type of space than within an open plan; however, doors and even deck-to-deck walls are often not enough to provide it.

Walls, windows, doors, ceiling tiles, and flooring reduce the volume of voice coming through the room’s physical structure, but even minor penetrations can seriously compromise its acoustic performance by allowing sounds to transmit into adjoining spaces.

If the background sound level in those spaces is lower than the speech passing through the wall, it will still be possible to hear and understand a conversation. In other words, the degree of speech privacy experienced in closed rooms is still largely determined by the signal-to-noise ratio. While masking levels should be set to achieve between 45 and 48 dBA within an open plan, closed rooms should typically be lower at 40 to 45 dBA. The doorway is a major challenge for a closed space. Even when closed, the door usually presents the weakest link, but when it is open, it does not matter how well the walls have been constructed, the level of sound isolation dramatically drops. For example, the effective rating of a 50 STC wall drops to 7 when the door to a typical 3-m (10-ft) wide office is opened. Most organizations do not want

Figure 6

AI tests also reveal the importance of properly tuning the sound masking in order to prevent large (i.e. greater than 1 dBA) variations in the coverage.

the doors to private offices to be closed at all times.

Sound masking, absorptive materials, and layout (e.g. staggering doorways along a corridor) should be used in order to continue to provide some degree of acoustic privacy when they are open.

Speech security Of course, eavesdropping can also be intentional, and handled in a much more sophisticated manner than leaning one’s ear against a glass and putting it up to the wall.

Though this article focuses on acoustic privacy rather than acoustic security—such as what may be required by military facilities, corporate boardrooms, or laboratories—it is important to know without the proper treatment windows, doors, ducts, pipes, floors, ceilings, and walls present opportunities for electronic forms of eavesdropping. Speech causes vibrations on these structures, which can be picked up by probes or microphones and translated into intelligible speech.

Further, these types of listening devices are difficult to detect because they can be used at a considerable distance from the target facility.

If an organization suspects it might be subject to such a threat, a sound masking system can be connected to transducers, which transfer the masking sound to the aforementioned physical structures, impeding the use of audio surveillance equipment. In this case, it is key to ensure the system produces a truly random masking sound

(i.e. rather than on a loop) so it cannot be filtered out of recordings.

Conclusion Attention must be paid to the topic of acoustic privacy within the built environment. Though this conclusion is obvious to organizations consistently dealing with sensitive information, the methods they use to achieve it are the same as those needed to accomplish other valuable acoustic goals—the only difference is how one sees the benefit: that is, from the perspective of the person talking or that of the group listening.

Building occupants working in an acoustically comfortable environment have an easier time concentrating on their tasks, and also suffer less stress and fatigue. An organization may decide it is more motivated by the need for a high-performance workplace than acoustic privacy, but taking the steps required to lower speech intelligibility allows them to reap both rewards.

Notes 1 For more information, see the study “Methods and Applications of the Audibility Index in Hearing Aid Selection and Fitting” by Amyn M. Amlani, MS, Jerry L. Punch, PhD, and Teresa Y. C. Ching, PhD. Visit www.ncbi.nlm.nih.gov/pmc/articles/ PMC4168961.

2 For more info, visit www.cbe.berkeley.edu/research/ briefs-survey.htm.

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Strategies for Sound Masking Part Four Sound advice on speech privacy

BY SEAN D. BROWNE

Sean D. Browne is the principal scientist for global acoustics at Armstrong Commercial Ceiling Systems. He is a member of the Acoustical Society of America (ASA), Audio Engineering Society (AES), and Institute of Electrical and Electronics Engineers (IEEE), Browne has engineering degrees from Florida State University and the University of Miami. He holds a patent for a power and signal distribution system for use in interior building spaces, and has been published in the journals of the International Symposium on Room Acoustics and the Acoustical Society of America. He can be reached at sbrowne@armstrong.com.

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All photos courtesy Armstrong Commercial Ceiling Systems

For Your Ears Only Sound advice on speech privacy

By Sean D. Browne

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he term ‘speech privacy’ refers to how well a conversation is overheard and understood by an unintended listener.

The need to prevent sound from intruding into adjacent spaces in both closed and open-plan settings is a concern in various buildings.

In healthcare settings, for example, patients can be exposed to situations in which they overhear conversations about other patients. In other instances, they risk having their own private information communicated in an environment where it can be heard by others. Examples include examination, consultation, treatment, patient, and meeting rooms, along with physicians’ private offices.

Research shows such scenarios are likely to impact patients’ trust and their ability to discuss their health problems freely with physicians, which can then have serious implications on their care.1 As a result, it is critical private conversations with or about a patient are not overheard.

Excessive sound in today’s healthcare facilities can also disrupt patient recuperation. Excessive noise in corridors and nurses’ stations can increase patient stress, or have a negative impact on comfort and recovery.2

The school classroom is another space where speech privacy is paramount, but for different reasons. According to the Acoustical Society of America (ASA),3 students only hear an average of 75 per cent of the spoken word in a classroom with poor acoustics.

(While this is a U.S. study, similar results would be expected for Canada.) One reason for this is the level of background noise intruding into their classroom from corridors and adjacent classrooms, as well as mechanical equipment above the ceiling.

High levels of background noise can mask speech, reducing the students’ ability to not only hear, but also understand their teacher. Moreover, teachers must speak louder to overcome the background noise, causing vocal fatigue. Sound-absorptive materials can reduce some of the background noise in the room. However, the best way to reduce it is to keep sound from intruding into the classroom in the first place.

In office buildings, employees have long considered intrusion of unwanted noise as one of the leading sources of workplace dissatisfaction. Over the years, study after study by the Centre for the Built Environment (CBE) points to noise as a major cause of reduced effectiveness, higher stress, and declining job satisfaction.4 SOUND MASKING | Construction Canada E-BOOK

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The Privacy Index is an especially important acoustical performance indicator in closed spaces.

Unfortunately, PI ratings for many closed spaces often indicate less than confidential speech privacy, even with doors closed. One reason is the walls in most closed spaces stop at the ceiling plane. They do not continue to the deck above.

Additionally, the rooms are generally not designed for dealing with raised voice levels, which is often the situation when dealing with elderly patients in healthcare facilities and students in classrooms.

The recognized levels of speech privacy—as defined by ASTM E1130, Standard Test Method for Objective Measurement of Speech Privacy in Open Plan Spaces Using Articulation Index, are broken down as ‘confidential,’ ‘normal or non-intrusive,’ ‘marginal or poor,’ and ‘no privacy.’

Reducing the level of speech intrusion from adjacent classrooms improves students’ ability to hear and to understand their teacher.

As the studies also indicate, many of the acoustical complaints relate to speech privacy—overhearing an unwanted conversation or simply feeling one is being overheard.5 Moreover, overheard conversations can lead to unintentional breaches of confidentiality in sensitive work areas. Keeping private conversations private is thus a key concern in conference rooms, executive offices, and other similar spaces in an office environment.

Additionally, the recently completed 2013 U.S. Workplace Survey conducted by Gensler indicates organizations offering ‘balanced’ workplace options that enable collaboration in open spaces without sacrificing the ability to focus in concentration areas are seen as more innovative and have higher-performing employees.6 As this type of workplace emerges, it will become increasingly important to attain speech privacy not only in traditional closed spaces, but also in focus or concentration areas in open spaces. The challenge in areas such as these will be to balance the need for privacy with the need for a dynamic teaming environment in one space.

Speech privacy levels The degree of speech privacy attained in a particular space is indicated by its Privacy Index (PI). It is expressed as a percentage, taking into account the acoustical performance of everything in the space, including ceiling, walls, floorcovering, furniture, and background noise level. The higher the percentage, the better the speech privacy.

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Confidential (PI rating of 95 to 100 per cent) Conversations within a space may be partially overheard, but definitely not understood beyond the confines of the space. Nearby occupants may hear muffled sounds, though the meaning of spoken words is not intelligible, and they are not distracted from what they are doing.

Normal or non-intrusive (80 to 95 per cent) Conversations can be partially overheard, and some words or phrases may be intelligible. Nearby occupants may hear some of the conversation, but the loudness of speech is not distracting—people can generally continue what they are doing.

Non-intrusive speech privacy is a common goal for open-plan environments. However, it is generally inadequate in functional environments with closed plans such as medical facilities, law firms, financial service organizations, or human resource departments, where confidential privacy levels are generally required.

Marginal or poor (60 to 80 per cent) Most conversations can be overheard and are likely intelligible. Nearby occupants can understand most words and sentences, and the loudness of speech can be distracting for them.

No privacy (60 per cent or less) All conversations can be clearly overheard and are fully intelligible. Nearby occupants can understand all words and sentences, and the loudness of speech can be a constant distraction.

Acoustical parameters To attain a specific level of speech privacy for a space, it is also important to be familiar with several of the acoustical performance parameters influencing it.

NRC The noise reduction co-efficient (NRC) indicates a ceiling’s ability to absorb sound from all angles. It is expressed as a number between 0.00 and 1.00, and indicates the average percentage of sound it absorbs.

An NRC of 0.6 means a ceiling absorbs 60 per cent of the sound striking it. The higher the number, the better the ceiling acts as a sound-absorber. A ceiling with an NRC less than 0.5 is considered low-performance, one with an NRC greater than 0.7 is high-performance.

CAC Ceiling attenuation class (CAC) is the acoustical ceiling performance parameter most associated with speech privacy. It indicates a ceiling’s ability to block sound in one space from passing up into the plenum and transmitting back down into an adjacent space that shares the same plenum.

CAC is an important consideration between adjacent closed spaces, as well as between adjacent closed and open spaces, and in open spaces where collaboration or teaming areas and focus or privacy areas are needed. It is measured according to ASTM E1414, Standard Test Method for Airborne Sound Attenuation Between Rooms Sharing a Common Ceiling Plenum.

The higher the number, the better the ceiling acts as a barrier to sound intrusion between the spaces.

A ceiling with a CAC less than 25 is considered lowperformance, one with a CAC greater than 35 is high-performance.

The right combination of NRC and CAC values represents the best approach to ceiling selection tailored to the needs of the space. When examining NRC and CAC values, specifiers should base ceiling selection on Underwriters Laboratories (UL)classified acoustical performance parameters.

A UL label on a carton certifies the ceiling panels have been tested by an independent third party on a continuing basis to ensure the panels’ performance meets or exceeds published values.

STC Sound transmission class (STC) indicates a wall’s ability to block sound transmission into an adjacent space. The higher the number, the better the

Keeping private conversations private is critical in executive offices, conference rooms, and other closed spaces in an office environment.

construction acts as a barrier to sound transmission.

A wall system with an STC less than 35 is considered low-performance, one with an STC greater than 55 is high-performance.

Balanced acoustical design in closed spaces The audibility of speech between adjacent closed spaces is not a problem until it becomes intelligible.

As a result, the main function of ceilings in closed spaces is to limit the transmission of sound between adjacent spaces, especially when the spaces share a common ceiling plenum.

Speech privacy in closed spaces can be achieved, even at raised voice levels, using balanced acoustical design with attention to the right combination of acoustical values. One of the most effective—and often least costly—methods for achieving speech privacy, balanced acoustical design consists of three key techniques: • a bsorbing sound within a space with highperformance acoustical ceilings that prevent sound from building up and intruding into an adjacent space; • blocking sound transmission between spaces with a combination of high-performance ceilings and effective partition wall design; and • c overing the remaining sound with an evenly distributed electronic sound masking system that can be adjusted to meet the desired privacy level.

For speech privacy, one can specify a mineral fibre acoustical ceiling installed continuously across the ceiling plane, and combines high ceiling attenuation (i.e. CAC 35 or higher) with moderate sound absorption (i.e. NRC 0.6 to 0.7).

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An acoustical ceiling with a CAC of 35 or higher is best in closed spaces to block sound from transmitting into an adjoining office, corridor, or open-plan area. It will also block sound from the adjacent space from intruding into the closed space, improving the acoustic environment of the closed space.

Ceiling panels offering a combination of a high CAC and a high NRC provide the best solution for both keeping noise levels down and conversations private in either closed or open-plan spaces.

Achieving the full privacy potential of closedplan spaces may also require the use of electronic sound masking. If so, co-ordinated performance between the sound masking and ceiling/wall system is essential. Each component must be engineered to ensure the design of the sound masking system complements the architectural performance over the key speech frequency range. The result will provide the appropriate level of speech privacy with the minimum level of masking sound.

Physician-patient confidentiality is a key concern in many healthcare spaces including examination rooms.

It may be necessary to supplement the ceiling system by providing closure/seal components to stop sound leaks around ceiling penetrations. It is especially important to control sound leaks around return air grills and light fixtures.

In terms of blocking noise, an effective combination of wall construction and ceiling must be specified. When space relocation is not an issue, a floor-to-slab fixed stud wall construction with a minimum STC 40 rating should be used. When relocation is problematic, either fixed stud walls or relocatable walls of floor-to-ceiling height with an STC 40 rating or higher and a ceiling with a minimum CAC 35 rating can be included.

All components of the wall system should be engineered for STC performance and for the removal of problematic sound leaks around doors, wall system joints, and seals at the ceiling and floor interface. Construction of the wall is critical since any crack in it or in the wall joints will allow sound to intrude into the adjoining space.

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A case study Attaining speech privacy depends on good acoustical design and proper material selection.

In this regard, the proper choice of a ceiling can serve to both limit the sound intrusion between spaces and affect the quality of sound within a space. It is a key element in creating an acoustical environment that can maintain speech privacy.

Marshall Erdman & Associates, an architectural firm known for healthcare facility planning, design, and construction, has long prided itself on protecting patient privacy by reducing sound transmission between rooms. One of the methods it used was a suspended acoustical ceiling in combination with rigid fibreglass insulation boards installed vertically as a plenum barrier between the top of a ceiling-height wall and the deck above. The panels in the acoustical ceiling had an NRC of 0.50 and a CAC of 33.

To improve patient privacy, the firm was looking for new ways to reduce sound intrusion levels between spaces even further while reducing construction costs. Installing the rigid insulation was extremely labour-intensive, so the firm desired a method that would provide the privacy level required while saving significant time and money.

Consequently, as part of the design of a Palos Hills, Ill., orthopedic clinic, the firm decided to

forego its traditional design and explore a new approach that eliminated the fibreglass plenum barrier and used a high-performance acoustical ceiling panel with ‘combination acoustics’—an NRC of 0.70 and CAC of 40.

Research showed it worked. Acoustical studies indicated a ‘confidential’ Privacy Index level was much more likely to be achieved in more circumstances than with the previous design.

Moreover, the installed cost of the CAC 40 ceiling with no plenum treatment compared to a traditional ceiling with fibreglass board plenum treatment was at least 40 per cent lower, based on the number of plenum walls removed.

Acoustics plus esthetics It is important to note that regardless of the space, esthetics do not have to be compromised when using a high-performance acoustical ceiling. Many of today’s highest-performing acoustical ceiling panels feature a popular smooth, fine-textured surface visual.

Additional options range from large panels more in scale with larger-sized spaces to panels with a unique edge detail that produces a 6.4-mm (¼-in.) reveal, minimizing visible grid and creating a ceiling plane more monolithic in appearance than ordinary suspended ceilings.

Panels are also available with a tegular or reveal edge to create a shadow line that helps camouflage the suspension system. In addition to their esthetic appeal, tegular ceiling panels provide better acoustical performance than square lay-in panels because there is less leakage at the interface between the panel and the grid.

Beyond traditional suspended ceilings, acoustical clouds or canopies can add enhanced acoustics in closed spaces such as conference and board rooms and in open spaces where focus and concentration are required. These free-floating ceilings provide esthetic appeal along with spot acoustics in the space below them, and can be customized to the needs of the occupants based on the desired outcome.

Conclusion The ability to isolate sound in these spaces through balanced acoustical design not only helps achieve speech privacy, but also increases speech intelligibility in an adjacent space by reducing the amount of noise intruding into it.

The main function of the ceiling in closed spaces is to limit the transmission of sound between adjacent spaces, especially when the spaces share a common plenum.

Adequate sound isolation also results in greater overall acoustic comfort and a reduction in noiseproduced annoyance.

Notes 1 For more, see Anjali Joseph’s 2006 article for the Center for Health Design, “The Role of the Physical and Social Environment in Promoting Health, Safety, and Effectiveness in the Healthcare Workplace.” Visit www.healthdesign.org/chd/research/role-physicaland-social-environment-promoting-health-safetyand-effectiveness-healthca.

2 See Joseph and Roger Ulrich’s 2007 article, “Sound Control for Improved Outcomes in Healthcare Settings.” Visit www.healthdesign.org/sites/default/ files/Sound%20Control.pdf.

3 This comes from “Classroom Acoustics: A Resource for Creating Learning Environments with Desirable Listening Conditions,” a 2000 publication of ASA’s Technical Committee on Architectural Acoustics.

4 Visit www.cbe.berkeley.edu/research/acoustic_poe.htm.

5 Visit www.cbe.berkeley.edu/research/acoustics.htm.

6 Visit www.gensler.com/uploads/documents/2013_ US_Workplace_Survey_07_15_2013.pdf.

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Strategies for Sound Masking Part Five Selecting the right ceiling for an office

BY CHRIS MARSHALL

Chris Marshall is the director of architectural sales for Rockfon’s stone wool acoustic ceiling assemblies. He has worked with specifiers, designers, installers, and manufacturers of stone wool products for more than a decade. Based in Toronto, Marshall earned a bachelor’s degree from the University of Windsor (Ontario) and an MBA from Western Michigan University in Kalamazoo.

He studied global supply chain management at Northwestern University’s Kellogg School of Management (Evanston, Illinois), participated in the Ivey Leadership Program through the University of Western Ontario’s Richard Ivey School of Business (London, Ont.), and was a student at Ontario’s York University’s Schulich School of Business in the executive program for sales leadership and management. Marshall can be reached via e-mail at chris.marshall@rockfon.com.

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Photos © John Lynch of Bochsler Creative Solutions. Photos courtesy Rockfon

Selecting the

Right Ceiling for an Office

By Chris Marshall

I

n the business world, how people work and interact is constantly changing, affecting how interior office spaces are designed and built.

Ceilings play an essential role in providing a productive, creative environment. Architects, designers, and specifiers who follow workplace trends will have a greater understanding of how to select different ceiling systems to best meet the needs of both employers and employees.

In the early 20th century, Frank Lloyd Wright saw the spaciousness and flexibility of an open-plan area as a way of liberating office workers from the confines of walled boxes. He and his contemporaries designed uninterrupted spaces with long rows of desks. Cubicles were later introduced, breaking

the rows into pods and islands. The most senior staff members were separated from the group into private offices lining the perimeter and enjoying the only available natural light.

Today’s employees can work from anywhere, anytime, enabled by wireless devices, social networking, and video conferencing tools. On any given day, in any typical office space, many workers are offsite, leaving their workstations unoccupied.

Consequently, the concept of ‘hot-desking’—where multiple employees share the same workspace at different times throughout the day or week—has become the norm in many buildings. This has enabled companies to increase the number of people working in the office without having to set SOUND MASKING | Construction Canada E-BOOK

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Suspension systems define the ceiling’s visible grid. Coupled with stone wool ceiling panels, the grid can be accentuated with a wide face, minimized with a concealed grid, or recessed for a shadow effect.

aside more space for workstations. Position and size of office no longer always equates to rank and seniority, increasing the learning opportunities between colleagues.

When employees are at an office, some are more productive and happier when they can interact freely with each other in a creative setting. An open-plan design can contribute to such an environment— the office itself can assist in achieving corporate goals, while protecting the positive elements of a corporation’s culture.

The heightened interaction and flexibility of the 21st century workplace is reflected in the increased use of exterior and interior glass, expansive floor spaces, integrated lighting, and contiguous ceilings with a monolithic appearance. Designers are creating inspiring spaces that reflect the energy and openness of the organization. Some take the notion of ‘openness’even further by showcasing formerly ‘hidden’ areas, such as production areas and meeting rooms, in aquarium-like fashion. In fact, many companies see their office space as a way of promoting their brand and values to visiting clients and prospective employees.

Companies that embrace an open-plan office design are moving beyond traditional meeting rooms to include informal communal spaces, like coffee bars or lounges encouraging impromptu

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connections. Atriums and hallways are configured to promote chance encounters and casual interaction.

High dividing walls are being replaced by lower partitions, or removed completely, encouraging employees to share ideas outside of scheduled meetings. Within the open-plan design scheme, some employers are designating quiet rooms when work requires greater reflection, confidentiality, and concentration.

Modern ceiling design Since the 1950s, suspended or ‘drop’ ceiling assemblies have been the preference in office settings with functionality frequently dictating appearance. Suspended ceilings consist of a metal grid comprising cross-tees and main runners. The main runners are suspended by hanger wires from the structure above, and wall channels or angles provide a clean look around the perimeter. Panels, air diffusers, lights, and other components are placed within the modular system. These conceal the plenum—hiding the structure, suspension system, HVAC, and other equipment, while providing simple access for future maintenance or renovations.

Historically, suspended ceilings’ appearance has been synonymous with the fibrous ceiling panels aged by their stains, broken corners, and visible,

Since the 1950s, suspended or ‘drop’ ceiling assemblies have been the preference in office settings with functionality frequently dictating appearance.

Acoustic comfort Designers of office work environments have to design not only for the eyes, but also for the ears.

The days of selecting an acoustic ceiling tile with moderate to high noise reduction co-efficient (NRC) and using it throughout all spaces no longer suffices from the perspective of people who spend their days in these environments. In a study of what employees found most dissatisfying about their work environment, sound privacy was the primary complaint for more than half of employees in open office plans, with dissatisfaction with noise levels making up another 25 per cent.2

Smooth and lightly textured surface finishes are a current design trend.

Stone wool ceiling panels’ porous material provides high sound absorption without showing deep fissures like old acoustic tiles.

Photos courtesy Rockfon

grey fissures. Today, acoustic ceiling panels are no longer limited to this dated appearance.

Smooth and lightly textured surface finishes are currently the design style of choice, giving an impression the ceiling is lighter in texture, weight, and colour. A bright, white finish also assists in addressing light reflectance in office buildings.

Stone wool ceiling panels are produced from basalt, the earth’s most abundant bedrock. It is inherently anti-microbial and achieves Class A fire protection, along with offering humidity, mould, and sag resistance. They also may be specified for impact resistance, seismic design categories, wind loads, and other requirements. One of its most recognized attributes, stone wool panels’ porous material provides high sound absorption without showing deep fissures like old acoustic tiles.1 Expanding modern ceiling design options, metal ceiling panels may be combined with stone wool panels or, in certain applications—such as in soffits—may be used alone. Usually, metal panels are fabricated from either aluminum or steel.

They can be manufactured with square edges to lay-in to a grid, or they can have reveal edges for a more decorative look. Baked enamel and powdercoat paints can be selected in nearly any colour, including metallics and simulated wood grain patterns. Metal panels can be perforated and backed by fibrous stone wool for sound absorption or left nonperforated when sound reflection is required.

Installed in the open-plan office, these stone wool ceiling panels provide a high level of acoustic control, along with easily cleaned surfaces, fire safety, humidity-resistant properties, and light reflectance.

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The heightened interaction and flexibility of the 21st century workplace is reflected in the increased use of exterior and interior glass, expansive floor spaces, integrated lighting and daylighting, and contiguous ceilings with a monolithic appearance.

Ceilings play an essential role in providing a productive, creative environment.

Characterized by brightness, openness and flexibility, open-plan offices with stone wool acoustic ceilings provide an inviting workplace for employees.

Achieving acoustic comfort comes from categorizing work functions according to desired acoustic experiences and intentionally designing various spaces with the appropriate acoustical characteristics. On any given day, some people will need to concentrate for long periods without disturbances. Quiet rooms, like quiet cars on a train, are needed. These rooms for either small groups or individuals are acoustically isolated from other areas of the office with full-height walls and heavy doors with perimeter seals to keep noise from breaking concentration. The ceilings are intentionally kept low and made of highly soundabsorptive fibrous panels of NRC 0.85 or higher.

At the same time, other people may be hosting a client and want to keep the conversation lively

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and accessible to draw in passing coworkers. In this case, the ceiling is raised higher and perhaps there are changes to ‘islands’ containing a mixture of sound-absorbing fibrous panels and soundreflecting metal panels. In other office designs, walls are selectively reduced in number and in height, or become acoustically translucent. This design approach intentionally allows some sound to permeate out to the immediate surrounding common areas.

Elsewhere in the office, a medium-sized group of people may be listening to a presentation. Here, speech intelligibility is the key acoustical criterion.

The ceiling becomes more sound reflective to project the presenters voice out to the group.

A common mistake made by designers is to place a highly sound-absorptive ceiling over an assembly space where speech intelligibility is required.

In large, open areas with numerous workstations, ceilings should maximize privacy and productivity by being low and comprised of highly sound absorptive fibrous ceiling panels of NRC 0.90 or higher. This physical component is often combined with electronic sound-masking to provide a normal speech privacy level despite the openness resulting from not having walls.

The key to acoustic success in contemporary office work environments is forethought about the numerous acoustic experiences needed by the occupants.

Intentional acoustic design uses various materials to provide spaces for quietness and concentration, social interaction, and privacy and confidentiality.

There are two main architectural components when designing an acoustic experience in a given space: sound insulation and sound absorption. Some ceiling panels can be specified with both properties in one product. The front side absorbs sound from the source room, while the back blocks sound coming from the plenum.

Sound insulation Sound-insulating techniques can reduce sound from transmitting from one space to another. Full-height

Stone wool ceiling panels may be specified for their light reflection to extend the sunlight more deeply into the workspace, which helps reduce the need for electrically powered lights (and the associated energy costs).

Renovation Considerations

A

s part of supporting a healthy, happy office environment, the freedom to roam and collaborate within an openplan office generates a greater need for flexible layouts.

Organizations need to be able to adjust workspaces accordingly. Sometimes referred to as ‘agile interiors,’ these spaces can be reconfigured relatively quickly and easily.

However, any change in floor plan requires a review of the ceiling plan to ensure the space’s acoustic performance keeps pace with the changing needs of its occupants.

By refurbishing and improving their current office layouts, companies can also accommodate more staff comfortably without having to move into larger premises. This helps keep costs down, increase operational flexibility, and meet employee expectations. To maintain the competitiveness, building owners who invest in renovating their existing properties enjoy higher occupancy and rental rates with longer-term agreements and more satisfied tenants.

In addition to preferring more modern, better quality spaces, many tenants are sensitive to the operating costs of offices and to achieving greater efficiency. First, there is economic efficiency. In a typical office building, more than half the total energy use is attributed to lighting, heating, and cooling. Making an old building more energyefficient will, therefore, reduce operating costs and offer a more comfortable climate—both of these factors can be important incentives for occupants.

Next, there is operational efficiency. Very often, older office spaces do not provide the level of HVAC, electrical, and IT services required today. Moreover, some office spaces were not designed to be offices in the first place.

When updating an old industrial building that has been

converted into office space, alterations may be needed to ensure that it meets current acoustic, fire, safety, and air quality regulations.

Finally, there is organizational efficiency. The way buildings are used evolves over time, and this is particularly true of office spaces. To improve the value of their assets, property developers are keen to upgrade existing, outdated, individual cellular office spaces to more commercially attractive open plans. Even in offices with open-plan landscapes, the layout may no longer match the organizational requirements.

One of the biggest and most frequent challenges in renovation projects is achieving acoustic comfort when the original room height is too low for a traditional suspended ceiling. Directly mounted ceilings can be a low installation height of just 31 mm (1.22 in.) when fixed directly to the soffit and can still achieve good sound absorption levels.

To preserve ceiling height in office spaces, the plenum above corridors often houses the majority of a building’s HVAC, mechanical, electrical, and plumbing systems.

However, concentrating these systems above the hallway leaves little room for traditional ceiling hangers and increases the noise level generated by services. Ceiling problems that can be suspended from the wall—even across large spans—help absorb hallway noise, reducing sound transfer from the plenum to adjacent rooms.

In historic buildings, acoustic ceiling panels, clouds, or baffles can be installed around architectural details such as high windows, structural beams, pillars, and other structural obstacles—maintaining these significant design elements, while improving acoustic performance.

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Companies that embrace an openplan office design are including informal communal spaces and hallway configurations to promote chance encounters and casual interaction. Intentional acoustic design provides spaces appropriate for lively social interaction, as well as for private concentration.

levels, and increases speech intelligibility. This creates a double effect—when the noise level is low, people talk more quietly. As a result, less noise is transferred to the adjacent rooms.

The two main contributors to sound absorption are high-quality fibrous ceilings and wall absorbers.

Sound absorption also has an indirect impact on room-to-room sound insulation. Using a highabsorbing ceiling in the source room reduces the sound in that room, resulting in less sound being transferred into the adjacent room.

walls—from floor to floor—are the most common because they are required by many standards and guidelines. They help maintain confidentiality and minimize disturbances from sound transfer between adjacent spaces. Another solution is to build the wall up to the suspended ceiling and use high sound-insulating ceilings. Ceilings also can be combined with sound barriers in the plenum installed directly above partition walls to further reduce sound transfer between enclosed spaces.

Sound absorption Porous treatments on the surfaces within a space absorbs sounds from people and equipment.

Absorption reduces reverberation time and noise

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Energy efficiency Heating and cooling are also the primary considerations in managing the large amounts of natural light that define today’s open plan office designs. Even in enclosed offices, workstations often have walls of complete or partial glass to allow in daylight. The less partitioned an open plan, the further daylight may travel into the building core. Ceiling panels may be specified for their light reflection to extend the sunlight more deeply into the workspace.

In a typical office building, more than half the total energy use is attributed to the lighting, heating, and cooling. Dimmers can be added to electrically powered lights to take advantage of particularly sunny days and reduce energy costs. On cloudy days and at night, reflective surfaces and ceiling panels assist the electric lighting in maximizing dispersal while minimizing resources and associated costs. Some offices also have reduced the number

The line of a ceiling impacts the perception of a space and creates focal points that may show direction, outline an object, or divide a large space into more comfortable zones.

of light fixtures needed from every 3.7 m (12 ft) to every 6 m (20 ft).3 Light quality and acoustic considerations are too often overlooked in parking garages and transit stations. For many employees, such locations are the first and last spaces they see during their workdays. When properly specified and installed, the ceiling systems in these areas will mostly go unnoticed in their goal of conveying a safe, welcoming environment.

Design trends Esthetically speaking, monolithic ceiling designs are standard in open-plan spaces. These designs combine the functionality of a ceiling suspension system with the creative potential offered by acoustic and metal panels in curves, clouds, mixed shapes and sizes, or flat, linear spans.

Suspension systems define the ceiling’s visible grid. This can be accentuated with a wide face, minimized with a concealed grid, or recessed for a shadow effect using bolt-slot suspension with a centre regress. Material and finish selection contributes to the appearance. Suspension systems usually are fabricated from: • aluminum, for most interior applications; • stainless steel, for more heavy-duty applications; or • steel with an aluminum cap option for those applications where environmental considerations are primary.

The suspension systems’ exposed metal face can be finished to either match or contrast with the panels.

White, silver, and black are frequently specified.

Most manufacturers offer a broad choice of painted colours or anodize finishes. Some include metallic hues, laminates, and options mimicking wood grain. Choosing a single-source supplier for metal panels provides consistency in both the finish and colour selection.

Along with the finish, metal panels can be specified with or without perforations. The perforations not only contribute to acoustical performance, but also enhance interior designs. The diameter of the holes can range from imperceptibly small to more than 15 mm (0.6 in.). The holes can be round or square, and placed tightly together or far apart; they can have lineal, diagonal, or staggered patterns. Some manufacturers offered graduated designs where the holes increase in dimension and decrease in spacing. Detailed, custom patterns also can be created for corporate logos, university mascots, and other pixelated graphic reproductions.

Compared with metal panels, acoustic stone wool ceiling panels are more limited in pattern and texture, but offer a broader selection of edge designs. Coupled with the range of suspension systems, the edge design can help to hide the grid with tightly fitted panels, shadow the grid with beveled recesses, obscure the grid with panels that seem to float under it, or emphasize the grid with square or angled tegular edges.

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Creative office designers are combining linear and curved lines, metal and acoustic panels, or different panel sizes, directions, and colours to make small rooms seem larger or produce inventive patterns.

Current trends in acoustic ceiling panels call for lightly textured or smooth finishes in white. Other than a bright white, natural tones are the most popular. Acoustic panel manufacturers usually offer a special palette of bold, metallic, pastel, and other hues. Custom blends may be provided to match school colours, company décor, or specific applications such as black panels for a theater. Colour choice can have a strong influence on occupants’ emotions, too.

Brighter colours, whether white or sky blue, convey a sense of energy. Paler colours tend to have a calming effect. Yellow and green are associated with health and well-being. Used purposefully, colourful panels can complement signage, helping visitors find their way.

By combining different module sizes, even small rooms may seem larger and long corridors less distant. The line of a ceiling impacts the perception of a space and creates focal points that may show direction, outline an object, or divide a large space into more comfortable zones. Horizontal lines convey stability, grounding, and direction. Vertical lines also communicate stability, along with pillar-like attributes of strength and balance. Diagonal lines are perceived as dynamic and transformational with overtones of freedom, while curves are considered playful, organic, and soothing.

More office building designers are combining linear and curved lines, metal and acoustic panels, as well as mixing sizes, directions, and colours. Intricate floor designs can be reflected in the ceiling design. Brickwork wall patterns can

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be replicated with staggered ceiling panel sizes. The serpentine shape of a riverbed viewed through the window can serve as inspiration for the ceiling’s curvilinear undulations.

Conclusion With the proper specification, installation, and maintenance, today’s ceiling systems can last for decades, evolving with the open-plan office design in order to meet the trends and functional needs for future workplaces.

Notes For more on this type of product, see the April 2014 issue of Construction Canada, which featured the article, “Far From Conventional: Looking up at Metro Toronto Convention Centre’s Ceiling Renovation,” by Scott Debenham. To read it, visit www.constructioncanada.net/far-from-conventionalmetro-toronto-convention-centres-ceilingrenovation.

2 See the article, “Workspace Satisfaction: The PrivacyCommunication Trade-off in Open-plan Offices,” by Jungsoo Kim, and Richard de Dear in the Journal of Environmental Psychology (36, 2013). For more on NRC, and metrics such as ceiling attenuation class (CAC) and articulation class (AC), read the article named in note 1.

3 Visit Facilitiesnet.com for the December 2010 article by Karen Kroll, “Study Links Green Buildings and Employee Productivity.”

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Compliant with CSI Formats & Guidelines