SCHOOL OF ARCHITECTURE, BUILDING AND DESIGN BACHELOR OF SCIENCE (HONS) IN ARCHITECTURE
BUILDING SCIENCE II (BLD 61303)
PROJECT 1 AUDITORIUM: A CASE STUDY ON ACOUSTIC DESIGN THE ACOUSTIC DESIGN OF CONNEXION@NEXUS
GROUP MEMBERS: AMOS TAN CHI YI 0318330 BRIDGET TAN SU TING 0318370 CHIA SUE HWA 0317920 KHOR YEN MIN 0318149 NATALIE KI XIAO XUAN 0318918 PHILIA CHUA YI SIAN 0318936 TOO MUN FAI 0318214
TUTOR: AR. EDWIN CHAN YEAN LIONG
Case study of Connexion@Nexus auditorium
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TABLE OF CONTENTS
NO.
ITEM
1
Introduction
PAGE 3
1.1 Aims and Objective 1.2 Site 1.3 Drawings
2
Acoustical Phenomena
7
2.1 Acoustics in Architecture 2.2 Sound Intensity Level (SIL) 2.3 Reverberation, Attenuation, Echoes and Sound Shadows 2.4 Issues of Acoustic Design Strategies 2.5 Acoustic Design for an Auditorium
3
Methodology
10
3.1 Equipment 3.2 Data collection method
4
Acoustical Analysis
12
4.1 Auditorium Design Analysis 4.2 Materials 4.3 Acoustic Treatments & Components 4.4 Sound & Noise Sources 4.5 Sound Propagations and Related Phenomena
5
Observation, Discussions & Conclusion
40
6
Referencing
41
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Figure 1: Panoramic view of auditorium house from stage
Figure 2: View of typical stage arrangement during events, with 2nd curtains deployed.
Figure 3: View of stage with all curtains retracted.
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1. INTRODUCTION 1.1 Aims and Objectives The aim and objectives of this report is to provide a concise and well-documented analysis that can showcase our understanding of our case study of acoustical theory in auditorium halls. Done so over the course of five to six weeks, the learning outcomes are as follows: 1. To study and develop an understanding of auditoriums through their design layout and judge its influence on the effectiveness of the acoustical design for its designated purpose. 2. To study the general acoustical characteristics of an auditorium hall and develop a good understanding of the physics behind their functions. 3. To be able to produce a well-documented report that surmises our findings and analysis of our case study – which can then serve as an example of our accumulated knowledge of the relationship between acoustics and space. By observing and analysing the types of acoustical design theories applied in the auditorium, we are then able to develop a better understanding on the characteristics of architectural space and how it affects the multiplicity of design approaches that can be taken for said space to be considered “acoustically efficient”. It is also important to know how different types of designs and their acoustical treatments influence the sound efficiency and the overall user experience. 1.2 Site 1.2.1
Basic Information Name of Auditorium Location
Type of Auditorium Year of Construction Year of Completion Total Volume Total Seats 1.2.2
: Connexion@Nexus Auditorium : Bangsar South City No. 7, Jalan Kerinchi, 59200 Kuala Lumpur, Malaysia : Multi-purpose Auditorium : 2012 : 2014 : 1022.77m³ : 298 fixed and cushioned seats
Historical background According to Anita Khoo, Head of UOA Hospitality, the idea behind the development of Connexion@Nexus was to provide an opportunity for the community to come together in a strategically nestled location between Bangsar, Kuala Lumpur city centre and Petaling Jaya for all kinds of activities including business, social and leisure. An entire floor within Connexion@Nexus (located at Level 3A) is dedicated to function rooms, ballrooms, a gazebo, as well as an auditorium, which became the auditorium of our choice. Serving as a multi-purpose auditorium, a variety of events are held here, including Annual General Meetings (AGM), business presentations, concerts, movie screenings, conferences, conventions, press conferences, product launches, product talks, seminars and training sessions. Case study of Connexion@Nexus auditorium
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1.3 Drawings 1.3.1
Connexion@Nexus Level 3A Floor Plan
1.3.2
Connexion@Nexus Auditorium Floor Plan
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1.3.3
Connexion@Nexus Auditorium Reflected Ceiling Plan
1.3.4
Connexion@Nexus Auditorium Section
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2. ACOUSTICAL PHENOMENA 2.1 Acoustics in Architecture Acoustics is the term used to describe the “science of sounds”. It deals with the study of all mechanical waves in matters such as gases, liquids and solids. “Sound”, however, can be defined as vibration in an elastic medium like gases, liquids (air, water) or any solid, physical object that can return to its normal state after being deflected. Sound can be reflected, absorbed, transmitted and diffracted. It is comparatively different to “noise”, though the two are often associated and mistaken for one another by the public. The difference is in its meaning; “sound” is any sort of vibration that can be deemed desirable, or pleasant, “noise”, on the other hand, is undesirable and often disturbing. Whilst it is often considered to be a hindrance, noise in its own service, is important. For example, the sounds of fire alarms or loud music can be deemed irritable, but can also be beneficial in certain cases when it can be controlled. Understanding these differences and knowing how to utilize building materials, system designs and technologies are key factors behind any successful acoustical design. While the science behind sound is well understood, using that knowledge to create an efficient acoustical performance within a specific building or room is a complex practice. There is no single “solution” or “formula” that can be universally applied to any building design as each built environment offers its own unique set of acoustical parameters. 2.2 Sound Intensity Level (SIL) Sound energy is conveyed to our ears (or instruments) by means of a wave motion through some elastic medium (gas, liquid, or solid). At any given point in the medium, the energy content of the wave disturbance varies as well as the square of the amplitude of the wave motion. That said, if the amplitude of the oscillation is doubled, the energy of the wave motion is quadrupled. The common method in gauging this energy transport is to measure the rate at which energy is passing a certain point. This concept is dubbed as “sound intensity”. Consider an area that is normal to the direction of the sound waves. If the area is a unit, namely one square meter, the quantity of sound energy expressed in Joules that passes through the unit area in one second defines the sound intensity. The time rate of energy transfer is then referred to as its "power" – written in the unit: “Watt” (1W is equal to 1 Joule/s). In simpler terms, this means that the sound intensity is the power per square meter. Normally, sound intensity is measured as a relative ratio to some standard intensity. The response of the human ear to sound waves closely follows a logarithmic function of the form “R = k logI", where “R” is the response to a sound that has an intensity of “I”, and “k” is the constant of proportionality. Thus, we define the relative sound intensity level as SL(dB) = 10log I Io The unit of SL is called a “decibel” (abbreviated as dB). “I” is the intensity of the sound expressed in watts per meter and “Io” is the reference intensity defined to be 10-12 W/m2. This value of “Io” is the threshold (minimum sound intensity) of hearing at 1 kHz, for a young person under the best circumstances. Notice that “I/Io” is a unit-less ratio; the intensities need only to be expressed in the same units, not necessarily W/m2. Case study of Connexion@Nexus auditorium
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2.3 Reverberation, Attenuation, Echoes and Sound Shadows Sound reverberation is the persistence of sound reflection after the source of the sound has ceased. Reverberation can have both a positive and a negative effect in architectural design. For example, specifying highly reflective ceiling panels directly above the stage area in an auditorium will help direct the sound toward specific seating areas, thus enhancing the room’s acoustical performance. However, that same reflective performance will become a negative factor if said highly reflective walls and ceiling materials are installed in the rear of the auditorium. That’s because the sound reflections from the rear of the room take too long to reach the audience, resulting in a distracting echo effect. When sound travels through a medium, its intensity diminishes with distance. In idealized materials, sound pressure (signal amplitude) is only reduced by the spreading of the wave. Natural materials, however, all produce an effect which further weakens the sound. This further weakening results from scattering and absorption. Scattering is the reflection of the sound in directions other than its original direction of propagation. Absorption is the conversion of the sound energy to other forms of energy. The combined effect of scattering and absorption is called attenuation. An acoustic shadow or sound shadow is an area through which sound waves fail to propagate, due to topographical obstructions or disruption of the waves via phenomena such as wind currents, buildings, or sound barriers. A short distance acoustic shadow occurs behind a building or a sound barrier. The sound from a source is shielded by the obstruction. Due to diffraction around the object, it will not be completely silent in the sound shadow. The amplitude of the sound can be reduced considerably however, depending on the additional distance the sound must travel between source and receiver. Sound reflection occurs when sound waves bounce off smooth, hard wall, ceiling and floor surfaces. Concave surfaces tend to concentrate or focus reflected sound in one area. Convex surfaces do just the opposite; they tend to disperse sound in multiple directions.
2.4 Issues of Acoustic Design Strategies Acoustical conditions in an enclosed space is achieved when there is clarity of sound in every part of the occupied space. For this to occur, the sound should rise to a suitable intensity everywhere with no echoes or distortion of the original sound, and with a correct reverberation time. Thus, these acoustical defects in buildings are important to recognize, diagnose and rectify. Acoustical reflectors or diffusers are implemented to evenly distribute the sound and to avoid areas where the sound quality is either weak, too excessive or cannot be heard clearly. Acoustic diffusion or sound reflection helps to provide a wider sound coverage for speech & music, and are often used to improve speech intelligibility and clarity in theatres, assembly halls, auditoriums, recording studios and classrooms. In addition to this, reflectors and diffusers are used to effectively reduce interfering reflections in any one direction by distributing the sound more evenly across the space.
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2.5 Acoustic Design for an Auditorium 2.5.1
Selection of the site The proposed site for the auditorium should be as far away as possible from noisy places, like railway tracks, roads with heavy traffic, airports, and industrial vicinities.
2.5.2
Volume The size of the auditorium should remain optimum: small halls leads to irregular distribution of sound because of the formation of standing waves. On the other hand, overly large halls create a weaker intensity and longer reverberation time which may result in serious hearing issues.
2.5.3
Shape and Form One of the most important parameters to be considered for an acoustically efficient auditorium design is the shape and form. Reflections are mainly created due to the presence of side walls and roof of the auditorium; thus, great planning is a must to ensure the reduction of echoes. In the case of parallel walls, splayed side walls are preferred. Curved surface on walls, ceilings or floors are also ideal when the aim is to produce a concentration of sound in a specific region.
2.5.4
Use of Absorbents When the construction of an auditorium is completed; there are still certain inaccuracies that require further improvements to achieve a better acoustical design. Hence, the use of absorbents is essential and a common strategy in amphitheatre design. They are often used at the rear wall of the amphitheatre, as well as the ceiling, as the reflection sound that occurs around these areas are of no benefit.
2.5.5
Reverberation Reverberation time must be controlled to be a perfect balance (e.g. 0.5 seconds for auditoriums, 1.2 seconds for concert hall and 2 seconds for theatres). The proper use of absorbent materials, the capacity of audience, presence of open windows, types of furniture used, are all examples of important components that affect the reverberation time.
2.5.6
Echelon Effect In an auditorium, any set of hand railings, staircases or any regular spacing of reflected surfaces may produce a musical note due to regular succession of echoes of the original sound. This disturbs the quality of the original sounds produced.
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3. METHODOLOGY 3.1 Equipment 3.1.1
Digital Sound Level Meter
Specifications Manufacturer Model Range Resolution Accuracy Frequency Microphone
LUTRON SL-4001 3 ranges: 35 to 130 dB (typical 30 to 130 dB), input signal only 0.1 dB Frequency weighting meet IEC 651 type 2 31.5 Hz to 8,000 Hz electric condenser microphone (1/2 inch standard size)
This device is used to measure the sound levels at a particular point within the auditorium. The unit of measure is decibels (dB). 3.1.2
Digital Camera
A digital camera is used to capture images of the existing context within our auditorium. These images would later be used as evidence to our analysis on how such components contribute to external noise, such as the finishing materials (including walls, floor, ceiling etc.), details of acoustic wall panelling or wall treatment, position of sound source (including speakers, poorly designed air conditioning or lighting systems etc.), occupancy level and activities carried out within the auditorium.
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3.1.3
Measuring Devices
Measuring tape
Laser Distance Measurer
These devices are used to obtain measurements of our auditorium for drawing and calculation purposes. They were also used to measure the distance of the sound level meter from the sound source when sound levels were taken.
3.1.4
Bluetooth Speaker
This device was used to test the acoustic performance of the auditorium by producing a constant sound (in terms of volume and frequency) at a single point as sound levels were taken from different distances.
3.2 Data Collection Method In order to achieve first-hand experience, formal arrangements were made prior to the visit ensuring that the auditorium would be unoccupied and allowing us to conduct a thorough investigation without disturbance. With the help of all preceding tools mentioned, we noted down as many details within our ability and constraints, including the auditorium’s layout & form, noise sources, furniture, materials and notable acoustic components. Measurements of the auditorium were also taken for drawing and calculation purposes, along with on-site sketches of the floor plans and sections for supporting any analysis.
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4. ACOUSTICAL ANALYSIS 4.1 Auditorium Design Analysis 4.1.1
Shape and Massing The auditorium’s overall shape is curvilinear, with one side of shorter length than the other. Concave walls line the left and right of the space, enclosing the seating area and stage within. This configuration hints to a poor acoustical design as concave shapes tend to naturally reflect and concentrate sound waves to the centre of its propagation (especially when majority of the sound source comes from the stage area), and which can only be countered with diffusion.
Figure 4.1.1: Expected sound path from plan. 4.1.2 Levelling of Seats The levelling of the seating area is of utmost importance to ensure that sound waves reach the ears of all occupants within the auditorium clearly. Given the scenario where the seats are not raised, the sound would not be able to travel all the way to the furthest-most seat as the vibrations would have been absorbed by only the first half, with majority of the sound waves dying out by the time it reached the second.
Figure 4.1.2: Level ground seat arrangement. Note weaker SIL as distance from source increases.
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Despite this, it can be solved by raising the stage, elevating it above the seats and allowing the sound source to project directly to all the occupants.
Figure 4.1.3: Elevated source arrangement reduces SIL loss. The seats within the Connexion@Nexus Auditorium are in the most effective configuration that defines the relationship between the speaker on stage and the audience. As such if they are raked (raised), they can increase the chance of allowing the occupants in the furthest-most seats to hear clearly. This is possible due to the effectiveness of the sound waves reaching the ears of the occupants when uninterrupted by any objects blocking or absorbing it.
Figure 4.1.4: Arrangement used by Connexion@Nexus ensures optimal sound travel to all audience members. 4.1.3
Arrangement of Seats The seats within the auditorium are arranged in a fan shaped configuration, to ensure a maximum number of seats are fitted, and to obtain an optimum view of the stage area from every seat. Most importantly, it helps achieve the most effective acoustic quality because sound waves travel in a spherical order. In addition to this theory, it is also important to note the angle of which the seating arrangements are fanned-out. It is tested that by including a 140-degree sound projection angle from the centre of the sound source on the stage. Should all seats fall within the angle of the sound projection area, the seating arrangement is well configured and deemed effective.
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Figure 4.1.5: Optimum 140 degrees wide layout ensures high frequency sounds are able to be discerned. 4.1.4
Ceiling Reflector Panels
The ceiling reflector panels included in the design forms a staggered ceiling configuration that aids in reflecting the sound back towards the seating area and increasing the volume of the sound as it reaches the ears of the occupants. As the height of the ceiling is not too great, the formation of echoes lessens and the panels serve their full purpose as a sound reflector whilst helping to distribute sound evenly throughout the auditorium. The increments of these sound levels are extremely important for the occupants at the last row.
Figure 4.1.6: Expected sound reflection from ceiling reflector panels to all audience members.
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4.2 Materials
AREA
MATERIALS
COMPO -NENT
COLOUR
SURFACE FINISHES
Acoustic timber veneer panelling
Maple brown
Glass curtain wall
Double glazing, 2-3mm glass, 10mm air gap
Smooth terrazo slabs
Stairs
Furniture
125 Hz
500 Hz
2000 Hz
Smooth
0.18
0.42
0.83
Transparent
Reflective
0.15
0.03
0.02
Slabs on concrete
Grey brown
Glossy
0.01
0.01
0.02
Timber stairs
Timber veneer, stainless steel and glass panels
Maple brown
Smooth
0.02
0.05
0.1
Steel and glass tables
Stainless steel and glass
Metallic silver
Shiny
0.07
0.14
0.14
Living room sofa set
Sofa set with leather covers
Beige
Leather
0.4
0.58
0.58
Apron absorbers
Fiberglass panel absorbers
Fiberglass on frame, 20mm cavity filled with rockwool
Beige
Soft fabric
0.15
0.75
0.8
Walls
Gypsum plaster on concrete
17% perforated, 22mm
Dark colour
Paint finish
0.03
0.02
0.04
PHOTO
Exterior
Walls
Flooring
Interior : Stage
COEFFICIENT
MATERIAL
DESCRIPTION
Timber wall
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Interior: House
Arch
Timber wall
Acoustic timber veneer panelling
Maple brown
Smooth
0.18
0.42
0.83
Flooring
Timber veneer flooring
Timber veneer panelling
Maple brown
Laminated
0.02
0.05
0.1
Curtains
Medium velour
Main act curtains x 1, valance curtains x5, rear curtain x 1
Maroon
Soft
0.03
0.15
0.5
Furniture
Tables and chairs
Clothupholstered
Dark brown
Soft fabric
0.5
0.45
0.6
Podium
Stainless steel and plastic
Metallic silver
Shiny
0.07
0.14
0.14
Doors
Solid timber door
Timber veneer door
Maple brown
Smooth
0.14
0.06
0.1
Upstage
Steel deck regging
Perforated mesh
Industrial black
Hard
0.13
0.08
0.11
Walls
Timber wall
Acoustic timber veneer panelling
Maple brown
Smooth
0.18
0.42
0.83
Fiberglass panel absorbers
Fiberglass on frame, 20mm cavity filled with rockwool
Beige
Soft fabric
0.15
0.75
0.8
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Flooring
Carpeted flooring
Medium pile carpet on rubber underlay
Brown pattern
Plushy
0.5
0.3
0.65
Seating
Upholstered tip-up seats
Vacant
Orange
Soft
0.33
0.64
0.77
-
-
Occupied by adult
-
-
0.33
0.44
0.45
Hand Railing
Stainless steel
-
Metallic silver
Shiny
0.07
0.14
0.14
Doors
Solid timber door
Timber veneer door
Maple brown
Smooth
0.14
0.06
0.1
Ceiling
Gypsum plaster ceiling
17% perforated, 22mm
White
Smooth
0.45
0.8
0.65
Control Room
Glass window
4mm glass, reflective solar film
Grey-black
Reflective
0.15
0.03
0.02
Figure 4.2.1: List of materials, its location, composition, and sound absorbency coefficient. This will be used for reverberation time calculations.
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Figure 4.2.2: Demarcation of areas within the auditorium.
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4.3 Acoustic Treatments & Components The multi-purpose function of this auditorium demands that it equally satisfies the acoustical needs of the multitude of functions it can cater for (concerts, speeches, assemblies, theatrical performances, and public gatherings). The general nature of large rooms with tall ceilings, wide shapes, and multiple hard surfaces such as these, tend to create very difficult listening environments. Sound waves naturally bounce off hard, reflective surfaces and create long reverberations and echoes throughout the room. Even with an expensive audio system, the sound is often muddled and tend to become unintelligible. The goal then, is to work within the confines of the room's existing construction and derive a clever solution using acoustical treatments to create an enjoyable listening atmosphere with perspicuous, intelligible sound. To achieve this, several acoustical treatments and components were taken into consideration in the design of the auditorium. To name a few are the timber veneer wall panelling, the timber stage flooring, the carpet flooring, the curtains, the padded seating, and the ceiling panels.
4.3.1
Wall Panels (Acoustic timber veneer panelling)
Figure 4.3.1: Acoustic panels mounted on the walls of the auditorium.
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Figure 4.3.2: Distribution of acoustic panel treatment.
The walls are designed in a concave shape – a form that can be perceived as both advantageous and disastrous. Concave surfaces tend to naturally concentrate and reflect sound to the centre of its projection – in this case, the audience seating area.
In this auditorium, it is unclear if the natural theory of sound reflection by a concave surface was the intent of the designer, however, its surfaces are covered with an absorptive material, quite possibly to reduce this effect. The first layer of fabric of the panels absorb a considerable amount of sound energy when it impinges on the fabric and its underlying high-density foam is used to control and reduce the reverberation. The air in the cells provide a resistance to the sound waves which loses its energy in the form of heat, however, this eliminates the sound’s ability to “ring” with clarity throughout the room during live events and instead can cause it to fall flat. The science behind this is very careful balance, especially because there is a fine line between a pleasant ring and an echoic mess. If sound rings too much, it can quickly – and dramatically –
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reduce the sound quality and the audience’s ability to hear clearly. The rear wall is treated with absorptive wall panels as well, which absorb the sound after it has passed over the audience and prevents a second wave (or “echo”) from occurring. The sequence of the wall panel’s material layering also counts. In this case, the surface of the wall panelling is the fabric, followed by the sponge - a porous material that can absorb high frequency sounds – and finished with plywood and rockwool, which is used to absorb the low frequency sounds. 4.3.2
Flooring
4.3.2.1 Stage (Timber veneer on concrete slab flooring)
Figure 4.3.3: Photo and section of stage floor.
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Figure 4.3.4: Location of stage on plan.
There are two main types of noise to be considered; the first is the higher frequency noise which comes from music, people talking and the like. This type of noise is controlled by mass of the floor system, mainly the mass or weight of the concrete, and the timber flooring that is layered over said concrete slabs, providing sufficient control for this not to be a problem. The second type of noise relates to the lower frequency vibrations. This includes sounds such as footfalls of people walking as well as the sound that emits from sub-woofers in the entertainment system. This low frequency tends to vibrate throughout the whole structure - including the slab. To control the low frequency vibrations, shock absorbing acoustic underlays play an important role in reducing the airborne and impact noise transmissions to an acceptable level. The concrete slab provides sufficient airborne sound insulation between the two habitable spaces, but are not adequate by itself to provide the required level of impact sound insulation. On the other hand, timber floorings are not as exceptional at providing airborne sound insulation as concrete slabs. Nonetheless, it is proficient for sound reduction with the addition of the concrete underlayment, adding a feeling of solidity to the floor and reducing the hollow percussive sound that footfalls can produce when the timber is floated over a subfloor without the benefit of an underlayment.
4.3.2.2 House (Pile carpet on rubber underlay) Case study of Connexion@Nexus auditorium
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Figure 4.3.5: Carpet and section of floor as used in the auditorium.
Figure 4.3.6: Carpeted areas shown highlighted.
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The thick carpeted flooring contributes to the sound absorption in the room. Carpet is an outstanding sound absorptive material which serves two functions – as a floor covering and as a versatile acoustical aid. Carpet absorbs the airborne noise as efficiently as many specialised acoustical materials, and its added rubber underlay offers a higher sound resistance to the absorption carried out by the carpet surface alone. 4.3.3
Curtain (Heavyweight velour)
Figure 4.3.7: Thick fire-rated curtains
Figure 4.3.8: Three distinct layers of curtains as used in the auditorium.
Thick, heavy, fabric curtains located backstage help control the reverberation by absorbing excess sound and eliminating the acoustic reflection off glass. Other than attenuating the chatter and noise in the room, it also provides tuneable acoustical and listening control in the auditorium. The highly porous material act as thousands of tiny sound traps, capturing the energy and turning it into heat. The pleated nature of the
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curtain (meaning it does not lay flat), exposes a more sound-absorbing surface, thus increasing the effective thickness and improving the low frequency sound attenuation.
4.3.4
Seating (Cloth-upholstered tip-up seats)
Figure 4.3.9: Upholstered seats.
Figure 4.3.10: Location of upholstered seats on plan. Other than offering acoustical taming throughout the room surfaces, added sound control is accomplished with the help of the padded seats. It adds to the acoustical absorption of an empty auditorium and allows the space to achieve a similar quality of sound whether the auditorium is filled to partial or maximum capacity. This can only Case study of Connexion@Nexus auditorium
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be achieved if the material is a padded fabric. A solid, hard material changes the acoustic performance of the auditorium depending on the number of occupants and the reflected sound vibrations.
4.3.5 Ceiling (Gypsum plaster)
Figure 4.3.11: Reflective ceiling panels
Figure 4.3.12: Reflective ceiling panels as shown on plan. Note the constant angle of the panels, which is not an optimal arrangement. The ceiling is an important factor for sound isolation. Gypsum plaster ceiling panels are used as they have smooth surfaces that aid sound reflection. They also provide for acoustical intimacy, clarity, and strength of the overall room’s sound. Suspended from the ceiling to provide short delayed, reflective sound energy, the reflector panels can provide the correct “ceiling shape� for early reflections that help avoid reverberation.
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This is also due to the human ear’s relative insensitivity to localizing sound on the vertical plane.
4.4 Sound & Noise Sources The term “sound” and “noise” are often to be considered one and the same, however, the term “noise” is subjective and relative to the listener’s point of view. To put it into simpler terms, “noise” is any sound that is considered undesirable by the occupant. How undesirable a sound is will depend on various qualities such as the loudness of the sound, frequency, continuity, time of occurrence, place, activity being carried out, information content, origin of the sound and even the personal state of mind of the listener. 4.4.1
External Noises Outside the Connexion Convention Hall, there are multiple origins of noise, namely the sound produced by the opening and closing of the doors as well as the sound of conversation taking place outside the hall itself. The noise produced by the people talking outside in the waiting and reception lobby can enter the auditorium via the doors as there is a lack of any sound proofing treatments on the doors. However, there is a sound lock within the inner and outer door at the main entrance of the auditorium. This serves to trap the sound waves within the sound lock and prevent them from interfering with the event inside, bringing the noise level from the outside down to less than 25dB for the seats nearby the door.
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Figure 4.4.1: shows the sound lock flanked by inner and outer doors that have door dampers. Beside the reception area, there is also an exterior alley running along the right side of auditorium that many occupants - especially crews and price receivers use to get to the front or back of the auditorium without disturbing the other occupants. Unfortunately, any noise from the people using the walkway can be easily heard in the auditorium itself due to the lack of any sound proofing on the doors or sound locks. Thus, the seats closer to the doors are exposed to roughly 50dB of noise disturbance. Door dampers are present on each end, however the noise from the act of the opening and closing of the doors itself are not reduced because of its excessive weight.
Figure 4.4.2: shows the walkway on the side of the auditorium – used for easy access to the front and back of the auditorium. 4.4.2
Internal Noises There are more unwanted noise sources from the interior of the auditorium, starting with the “whoosh” noise that comes from the air conditioner diffusers, footsteps on the carpet & stage, as well as the doors leading to the backstage and AV room. The stage of the auditorium, which is paved with a layer of timber veneer for aesthetics, causes incessant “thudding” sounds when stepped on. The air gap below its concrete platform, which is used for amplifying the subwoofers below the stage, also contribute to the noise of the footfalls.
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Figure 4.4.3: shows the material composition of the stage and auditorium floor
Figure 4.4.5 and 4.4.6: shows the hollow space under the stage dedicated for subwoofers and the carpeted floor of the auditorium with rubber coating beneath respectively.
The linear air conditioning diffuser system runs along the gaps of the suspended acoustic ceilings is long, narrow strips, and is designed for forcing air-conditioning into the space. This causes an undesired and unnecessary “whoosh� sound of the forced air that can be heard easily by the audience seated below. Consequently, the creation of constant and steady noise will affect the quality of the events held in the auditorium.
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Figures 4.4.7 and 4.4.8: indicates the rows of air conditioner diffusers lined along the gaps of ceiling panels The doors located around the sides of the auditorium also produce sudden and temporary noise disturbance for the audience seated in the hall. The average dB produced from the banging of a door is around 80dB, but while the door dampers included serve to lessens the noise to roughly 60Db, the actual noise produced by the opening and closing of doors are still very noticeable from any seat in the auditorium.
Figures 4.4.9: indicates the location of origin of interior and exterior noise produced by doors and people talking outside the hall.
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Figures 4.4.10: shows the sectional view of the auditorium which shows the origin of noise produced by the air conditioner diffusers and walking footsteps.
Figures 4.4.11: Noise sources and intensity from ceiling. Noise is distributed throughout the auditorium at relatively high volumes, causing unpleasantness.
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4.5 Sound Propagations and Related Phenomena The measurement of the auditorium from a fixed sound source, outputting a constant 500Hz tune at 80dB, has resulted in the following findings: 1. The auditorium layout has resulted in the creation of unpleasant sounds at certain spaces. 2. There is an inefficient use of materials. 3. The auditory classification of the auditorium as a “dead space�. The rationale of said findings are as follows: 4.5.1
Sound concentration The measurement of the sound intensity level (SIL) from the sound source, shows that there is a distinct sound concentration zone can be found at the centre-back of the auditorium.
Figure 4.5.1: SIL measurement of the auditorium.
This is despite the (inefficient) coverage of acoustic panelling found on virtually every wall surface in the auditorium. It appears that the curvilinear form of the auditorium has a detrimental acoustic quality, and has created some auditory foci within, amplifying sound in the specific areas.
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Figure 4.5.2: Sound reflection diagram. Note the detrimental design of the auditorium layout. The creation of this sound concentration zone is offset by the overly excessive usage of sound absorbent materials – in this case, defined as materials that have a sound absorbency coefficient lower than 0.1.
Figure 4.5.3: Sound reflection diagram with materials. Note the over excessive use of absorbent materials. It is evident that the designer of this auditorium has taken steps to reduce the impact of the sound concentrated areas, with the result being only 3dB higher in concentration than the surrounding spaces.
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4.5.2
Sound reflections In order to make the use of sound more efficient, it is necessary for the sound to be reflected back towards the audience. However, the amount of sound reflected, with the added design of these reflections, must be carefully controlled to minimize the creation of echoes.
Figure 4.5.4: Sound propagation towards subject at Row 6. Ceiling reflectors serve to reflect sound effectively back to the audience. Nevertheless, the rest of the auditorium then must be covered with absorbent materials which can minimize the resultant reflected sound, making it almost indiscernible.
Figure 4.5.5: Sound propagation toward Row 1. Note lack of reflected sounds.
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Figure 4.5.6: Sound propagation towards Row 11. Note large amount of reflected sounds While the auditorium has presented itself many opportunities to create a rich and lively soundscape, due to the combined use of over excessive reflective surfaces, the choice of materials as well as other factors, it has severely hampered the experience, and will lead to the creation of an auditory “dead space�. 4.5.3
Echoes and Sound Delay An echo is distinctly different from a reverberation as it is a constant repetition of the original sound. The nature of the programme influences the desired sound delay period and thus, the definition of its echo. In this analysis, only reflective surfaces will be treated as effective sources of sound delay. Generally, in an auditorium designed for speeches, any sound delay above 40ms will be considered as an echo, while an auditorium designed for music will consider any sound delay above 100ms as an echo.
Figure 4.5.7: 8.23ms sound delay is acceptable for a speech-oriented auditorium.
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Figure 4.5.8: 13.8ms sound delay is acceptable for a speech-oriented auditorium.
Figure 4.5.9: 2.1ms sound delay is incredibly short, even for a speech oriented auditorium. The sound delay present in this auditorium is so miniscule that it is difficult to discern. As such, this auditorium will not suffer from any intelligible sound caused by echoes.
4.5.4
Reverberation Reverberation is key in the perception of spaces being either “lively” or “dead”. Generally, reverberation is a desirable element regardless of the programme, and having too little reverberation time will result in people perceiving an auditory “dead space”. With that said, having too much is also deleterious, and could lead to intelligible sound or echoes. A desirable reverberation time depends on the type of space, as noted in the graph below:
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Figure 4.4.10: Desirable reverberation time depending on programme. Source: https://acousticalsolutions.com/wpcontent/uploads/2015/04/reverb_time_chart_525.jpg
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It is in this aspect that Connexion@Nexus suffers greatly. Due to the extensive use of absorbent materials covering of the auditorium, coupled with the relatively small volume, its reverberation time is extremely low.
Figure 4.5.11: Reverberation time of Connexion@Nexus A reverberation time of just 0.26 seconds is only suitable in a studio environment, and unequivocally not in an auditorium. As such, this auditorium can be (and is perceived by its users) as an auditory dead space.
4.5.5
Acoustical Defects and Design Issues
Besides the extremely low reverberation time, this auditorium also suffers flutter echoes from its inefficient design. Despite the low sound delay time present in the house itself, flutter echoes tend to occur on stage. This is because of the parallel surfaces between the ceiling and the stage floor, both of which are defined as reflective materials.
Figure 4.4.12: Flutter echoes and inefficient ceiling reflector design.
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Furthermore, nearly half of the ceiling reflectors present in the auditorium are not effective. They tend to reflect any sound right into the back wall – which is covered with absorbent acoustic panels as well. This is an inefficient use of the available sound energy, and would be of a better design had it been angled to allow the reflections back towards the audience instead.
4.5.6
Connexion@Nexus as a Speech Auditorium Connexion@Nexus advertises itself as a “multipurpose auditorium”, however, most events held within this auditorium are seminars, speeches and lectures; events of voice and not music. The lack of echoes is important to ensure the clarity of the speeches performed at the auditorium, and with no distinct repetition of sounds, the audience would be able to perceive every word spoken clearly. This is due in part to the liberal use of absorbent materials, which greatly limits and controls the degree of which reflections can occur. While the layout of the auditorium itself has created a sound concentration area, it has been tackled arguably successfully with the use of absorbent materials. Even so, it is the heavy use of absorbent materials that has led to it having an extremely low reverberation time of 0.26 seconds. This will lead the sound to seem flat and can cause the speeches to be perceived as being “dead” and “boring” as the sound does not have a “ring” to it. Unfortunate as it is, with the help of electronic audio/visual suite, Connexion@Nexus may be able to narrowly overcome this hurdle.
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5. OBSERVATION, DISCUSSIONS AND CONCLUSION To sum up a conclusion from our accumulated findings and subsequent analysis, Connexion@Nexus is an auditorium that is generally unsuited for any live performances which are unassisted and unamplified. Its dependence on electronic audio/visual suites to overcome its shortcomings is still not a guarantee to its ability to serve as an acoustically efficient auditorium, and many events are still held within its hall despite its issues. Though it has been advertised as a “multipurpose” auditorium, due to its suboptimal layout, numerous sources of unnecessary noises, and poor use of acoustical components, its overall approach and operation strongly suggests a focus towards speech-related events only. The measures which have been taken to the acoustical sensitivity are – in our opinion - mediocre at best, and whilst the basic theories of acoustics have been applied, various key principles have also been ignored, further demonstrating that the knowledge is comparatively shallow and far less sensitive to its true potential.
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6. REFERENCING
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Shapes and Sounds: Designing concert halls with curves. (n.d.). Retrieved April 30, 2017, from https://www.constructionspecifier.com/shapes-and-sounds-designing-concert-halls-withcurves/
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Inc., T. S., Says, J., Says, N., Says, R. C., Says, E., Says, H. S., & Says, S. (2017, February 21). Auditorium Seating Layout & Dimensions Guide. Retrieved April 30, 2017, from http://www.theatresolutions.net/auditorium-seating-layout/#floor-design
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