SCHOOL OF ARCHITECTURE, BUILDING AND DESIGN BACHELOR OF SCIENCE (HONS) IN ARCHITECTURE
BUILDING SCIENCE II (BLD 60803) Project 1 Auditorium: Case study on Acoustic Design
Leong Darren Low Wing Chun Joey Lau Xin Jun Cryslyn Tan Zhia Lyn Tung Siew Hui Tan Ke Weh Ong Jie En Vun Tze Lin Shreya Maria Wilson
0323645 0323315 0323965 0324249 0323823 0323799 0323835 0323301 0322173
TUTOR AR. EDWIN CHAN
TABLE OF CONTENTS Topic 1.Introduction 1.1 Aim & Objective 1.2. Site 1.2.1 Site introduction 1.2.2 Historical Background 1.2.3 Plenary Hall 1.3. Drawings 2. Acoustical Phenomena 2.1 Acoustics in Architecture 2.1.1 Sound Intensity Level (SIL) 2.1.2 Reverberation Time (RT) 2.2 Reverberation, Attenuation, Echoes and Sound Shadows 2.3 Issues of Acoustic Design Strategies 2.3.1 Reverberation time 2.3.2 Loudness 2.3.3 Focusing 2.3.4 Echo 2.3.5 Echelon effect 2.3.6 Resonance 2.4 Acoustic Design for an Auditorium 2.4.1 Selection of site 2.4.2 Volume 2.4.3 Shape and volume 2.4.4 Use of absorbents 2.4.5 Reverberation 2.4.6 Echelon effect 3. Methodology 3.1 Equipment 3.2 Data collection method 4. Acoustical Analysis 4.1 Auditorium Design Analysis 4.1.1 Shape and Massing 4.1.2 Levelling of seats 4.1.3 Arrangement of Seats 4.2 Materials 4.3 Acoustic Treatments & Components 4.3.1 Wall panels 4.3.1.1 Timber Perforated Acoustic Panel 4.3.1.2 Acoustic Wall Panel 4.3.2 Seating 4.3.3 Ceiling 4.3.4 Flooring 4.3.4.1 Stage Flooring 4.3.4.2 Audience Flooring
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TABLE OF CONTENTS Topic 4. Acoustical Analysis 4.4 Sound & Noise Sources 4.4.1 External Noise 4.4.2 Internal Noise 4.5 Sound Propagations and Related Phenomena 4.5.1 Sound Concentration 4.5.2 Sound Reflection 4.5.3 Sound Shadow 4.5.4 Sound Echo and Delay 4.5.5 Reverberation 4.5.6 Acoustical Defects & Design Issues 4.5.7 Plenary Hall as a “Multipurpose Auditorium
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5. Observation, Discussions & Conclusion
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6. References
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1. Introduction 1.1 Aim & Objective In a group of 9 people, we were tasked to conduct a case study on a chosen auditorium hall, in this case being the Plenary Hall of Putrajaya International Convention Centre (P.I.C.C), and to produce a brief but comprehensive report on the acoustic quality it possesses. Objectives of this case study includes:1. To understand and study the acoustics quality in the auditorium based on factors such as the design layout, choice of exterior and interior envelope, sound absorption and reflection materials and more. 2. To develop a deeper understanding by analyzing the characteristics that makes it a good auditorium. 3. To produce a well documented analysis report based on our observations and data collection from the site visit.
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1.2 Site 1.2.1
Site introduction
Putrajaya International Convention Centre (P.I.C.C) is Malaysia’s premier meeting and convention venue placing first in exclusivity, number and variety of venues, access and connectivity and green practices. It is both an iconic landmark that overlooks Malaysia’s seat of government and one that incorporates a modern, spacious and incredibly versatile design while embodying a further, cultural dimension.
(Figure 1.2.1 Putrajaya International Convention Centre)
Location: Architect: Client: Built Area: Number of venues: 1.2.2
Presint 5, 62000, Putrajaya Hijjas Kasturi Associates Jabatan Perdana Menteri 135,000 sqm 49 over 9 levels
Historical Background
Construction of the convention centre began in 2001 and finished in September 2003. The first conference held in P.I.C.C was the 10th Islamic Summit organised by the Organisation of Islamic Cooperation (OIC) in October of the same year. In October 2004, the Putrajaya Convention Centre was officially renamed to the Putrajaya International Convention Centre. The front of the building is engrafted with a thorough combination of ‘Wau’, an ancient kite popular in the two Malaysian states of Terengganu and Kelantan, and the ‘Pending Perak', a silver royal like belt buckle, is also seen in the main hall. The P.I.C.C is the brainchild of Malaysia’s fourth Prime Minister, Tun Dr Mahathir Mohamad.
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1.2.3
Plenary Hall
The Plenary Hall is P.I.C.C’s largest single venue, imposing gallery-like auditorium ideal for major functions, ranging from speech,musical performances, meetings and many more - in short, any event requiring the highest level of functionality and grandeur. It has a total volume of 52173 cubic meters and seats 3000 people. The interior design is inspired by Malaysian traditional mengkuang basket weave motif, which also enhances illumination from natural daylight.
(Figure 1.2.2 Panoramic view of hall from stage)
(Figure 1.2.3 Panoramic view of hall from back)
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1.3 Drawings
(Figure 1.2.5 Site plan of PICC)
(Figure 1.2.6 North elevation of PICC)
(Figure 1.2.7 Section of PICC)
All drawings N.T.S
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(Figure 1.2.8 Floor plan of plenary hall)
All drawings N.T.S
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2.
Acoustical Phenomena
2.1
Acoustics in Architecture
Acoustic 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 (air, water) or any solid, physical object that can return to its normal state after being deflected. Acoustics in the built environment is usually evaluated on noise curve and reverberation time (RT). If the hall is to be acoustically satisfactory, it is essential to have the right reverberation time. The sound absorption materials are rated with sound absorption coefficient which are affected by the fiber or material size, volume of fiber, porosity, air flow resistance, thickness, density, compression and placement or position of materials. As architects, it is important to understand architecture acoustics and how the behaviour of sound can affect the space within. Knowing and understanding the properties of sound help architects to control or manipulate the sound behaviour through the design of the space.
2.1.1
Sound Intensity Level (SIL)
Sound intensity is defined as the sound power per unit area. The general context is the measurement of sound intensity in the air at a listener's location and the basic units are watts/m2 or watts/cm2. Many sound intensity measurements are made relative to a standard threshold of hearing intensity I0, which is
However, sound intensity levels are quoted in decibels (dB) much more often than sound intensities in watts per meter squared. Decibels are the unit of choice in the scientific literature as well as in the popular media. The reasons for this choice of units are related to how we perceive sounds. How our ears perceive sound can be more accurately described by the logarithm of the intensity rather than directly to the intensity. The sound intensity level β in decibels of a sound having an intensity I in watts per meter squared is defined to be
Where I0 = 10−12 W/m2 is a reference intensity. I0 is the lowest or threshold intensity of sound a person with normal hearing can perceive at a frequency of 1000 Hz. Sound intensity level is not the same as intensity. Because β is defined in terms of a ratio, it is a unitless quantity. The units of decibels (dB) are used to indicate this ratio is multiplied by 10.
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2.1.2
Reverberation Time (RT)
Reverberation Time (RT) Reverberation is the prolongation of sound as a result of successive reflections in an enclosed space after the sound source is shut/turn off. Reverberation Time is the time for the sound pressure level in a room to decrease by 60dB from its original level after the sound is stopped. It varies due to the following factors: the room volume, materials used, and sound sources. RT can only be measured when it is an enclosed space. RT = 0.16V / A Where, RT = Reverberation time (sec) V = Volume of the room (m Âł ) A = Total absorption of room surfaces RT is influenced mainly by the acoustic absorption within the enclosed space and each material has its own material absorption coefficient. This question allows us to analyse on the effectiveness of the absorption of materials used in the selected site.
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2.2
Reverberation, Attenuation, Echoes, and Sound Shadows
Reverberation is the collection of reflected sounds from the surfaces in an enclosure like an auditorium. It is a desirable property of auditoriums to the extent that it helps to overcome the inverse square law dropoff of sound intensity in the enclosure. Hard surfaced rooms normally will have a longer reverberation time than rooms finished with sound absorbing materials. When a sound wave travels outward in all directions and encounters an obstacle such as a wall, floor or ceiling surface, the direction of the sound will change or reflected. The direction of travel of the reflected sound will be at the same angle as the original sound striking the surface. However, if it is excessive, it makes the sounds run together with loss of articulation and the sound would become muddy and garbled. When sound travels through a medium, its intensity diminishes with distance. This weakening in the energy of the wave results from two fundamental causes: scattering and absorption. Scattering is the reflection of sound in directions other than its original direction of propagation. Absorption is the conversion of sound energy to other forms of energy. The combined effect of scattering and absorption is called attenuation.
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2.3 2.3.1
Issues of Acoustic Design Strategies Reverberation time
If a hall is to be acoustically satisfactory, it is essential that it should have the right reverberation time. The reverberation time should be neither too long nor too short. A very short reverberation time makes a room ‘dead’. On the other hand, a long reverberation time renders speech imperceptible. The optimum value for reverberation time depends on the purpose for which a hall is designed. 2.3.2
Loudness
Sufficient loudness at every point in the hall is an important factor for satisfactory hearing. There would require a need of balance between sound absorption and reflection to ensure the loudness of the sound. 2.3.3
Focusing
Reflecting concave surfaces cause concentration of reflected sound, creating a sound of larger intensity at the focal point. These spots are known as sound foci. Such concentrations of sound intensity at some points lead to deficiency of reflected sound at other points. The spots of sound deficiency are known as dead spots. The sound intensity will be low at dead spots and inadequate hearing. Furthermore, if there are highly reflecting parallel surfaces in the hall, the reflected and direct sound waves may form standing waves which leads to uneven distribution of sound in the hall. 2.3.4
Echo
When the walls of the hall are parallel, hard and separated by about 34m distance, echoes are formed. Curved smooth surfaces of walls also produce echoes. 2.3.5
Echelon effect
If a hall has a flight of steps, with equal width, the sound waves reflected from them will consist of echoes with regular phase difference. These echoes combine to produce a musical note which will be heard along with the direct sound. This is called echelon effect. It makes the original sound unintelligible or confusing. 2.3.6
Resonance
Sound waves are capable of setting physical vibration in surrounding objects, such as window panes, walls, enclosed air etc. The vibrating objects in turn produce sound waves. The frequency of the forced vibration may match some frequency of the sound produced and hence result in resonance phenomenon. Due to the resonance, certain tones of the original music may get reinforced that may result in distortion of the original sound.
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2.4 2.4.1
Acoustic Design for an auditorium Selection of site
The location of the site plays a big role for the acoustical design. The selected site should be located far from places with large amounts of noise such as airports, railway tracks and industrial areas for better acoustic quality. 2.4.2
Volume
The size of the hall should remain optimum, as small halls would cause uneven distribution of sound due to the formation of stationary waves while overly large halls would create longer reverberation time that would result in unpleasant sound. 2.4.3
Shape and volume
The use of splayed walls instead of parallel walls enhances the acoustical quality of the hall. Curved surfaces should be built with proper care to produce a concentration of sound in a particular precinct. Proper design is also a necessity to assure the reduction of echoes. 2.4.4
Use of absorbents
As the correct use of absorbent enhances the acoustic quality of an auditorium, it is a common and crucial strategy of design. They are often used on the rear wall of the auditorium, as well as on the ceiling. 2.4.5
Reverberation
The reverberation time can be controlled by the suitable choice of building materials and furnishing materials. Since open windows allow the sound energy to flow out of the hall, there should be a limited number of windows. They may be opened or closed to obtain optimum reverberation time. In order to compensate for an increase in the reverberation time due to an unexpected decrease in audience strength, upholstered seats are to be provided in the hall. 2.4.6
Echelon effect
The echelon effect may be remedied by having steps of unequal width. The steps may be covered with proper sound absorbing materials such as carpet.
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3.
Methodology
3.1
Equipment Digital camera A digital camera was used to record videos and images for referencing later on. The images would be later used as evidence based on our research and analysis.
(Figure 3.1.1 Digital camera)
JBL Flip 3 Portable Wireless Speaker Output power: 16W (Figure 3.1.2 Speaker)
Frequency response: 85Hz – 20kHz Speaker used to produce sound at a constant level of frequency and volume at a single position of output to measure SIL at different points.
Sound meter A sound meter was used to measure the different sound levels at different points in the auditorium. It responds to the change of air pressure caused by sound waves. The unit of measure is sound decibels (dBA)
(Figure 3.1.3 Sound meter)
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Tone Generator: Audio Sound Hz Tone generation mobile application developed by TMSOFT. Allowed us to produce a constant level of frequency and transmitting it via bluetooth to our portable speaker. Tested frequency : 125Hz, 500Hz, 2000Hz
(Figure 3.1.4 Tone generator)
Bosch DLR130K Digital Distance Measurer Two sets of laser distance measurer was used to measure the distance of the sound source from the sound level meter accurately as well as to measure distances of the auditorium for calculation purposes.
(Figure 3.1.5 Laser distance measurer)
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3.2
Data Collection Method
To assure that the site visit could be carried out smoothly and without interruption, formal arrangements were made with the person in charge, Mr.Saifuddin, to ensure that the auditorium would be unoccupied during our visit, enabling us to conduct our case study. We documented as many details as possible during the visit with the help of all the tools mentioned along with all the necessary measurements required to assist our analysis. We also compiled the questions we had such as the materiality of items and its function and forwarded to the technical team in order to get correct data and information.
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4.
Acoustical Analysis
4.1 4.1.1
Auditorium Design Analysis Shape and Massing
The P.I.C.C auditorium’s overall shape is curvilinear, shaped as a circle. The design of the concave walls would apparent the concentration of sound to a focal point as such of the law of reflection on a concave surface. This configuration would hint poor acoustic design particularly at such a large scaled hall. However, the designer made usage of absorbent materials across the walls of the hall, countering the effect of the concave sound reflection.
Figure 4.1.1.1: Apparent sound path without the usage of sound absorption materials on the wall
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4.1.2
Levelling of seats
The levelling of the seating area is of utmost significance to ensure that the sound waves reach to the ears of all audience within the auditorium clearly. It is given that 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 the majority of the sound waves drain out by the time it reached the second .
Figure 4.1.2.1: Level ground seat arrangement. Note weaker SIL as distance from Source increases.
Despite that, this can be solved by elevating the stage, raising the stage above the seats level, allowing the sound source to project directly to all the audience.
Figure 4.1.2.2: Elevated source arrangement reduces SIL loss.
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The seats within the Plenary Hall are in the most effective configuration that defines the relationship between the speaker on stage and the audience. As such, if they are 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 the objects blocking or absorbing it. Fundamentally this is the very basic acoustical design element that a designer can apply. However, the Plenary Hall requires the need of sound reinforcement due to its large scale.
Figure 4.1.2.3: Arrangement used by PICC ensuring optimal sound travel to all audiences.
4.1.3 Arrangement of Seats The seats within the entire auditorium are arranged in a fan shaped configuration. It is not only to ensure a maximum number of seats are fitted, but also to obtain an optimum view of the stage area from every seat’s perspective. Most importantly, it can help to achieve the most effective acoustic quality due to the sound waves travel in a spherical order. Moreover, it is also significant to set the angle of which the seating arrangements are fanned-out. Furthermore, the seats fall within the angle of the sound projection area (140 degree), and is well configured and deemed effective.
Figure 4.1.3.1: Optimum 140 degrees wide layout ensures high frequency sounds are able to be discerned.
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4.2 Materials Figure 4.2.1 - Diagrams of floor plan denoting zoning of areas
Exterior
Interior: House
Interior: Stage
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4.2
Materials
AREA
MATERIAL PHOTO
SURFACE FINISHES
MATERIAL
DESCRIPTION
Exterior (Wall)
Timber wall
Timber veneer panelling
Exterior
Glass curtain wall
Exterior (Flooring)
COEFFICIENT 125 Hz
500 Hz
2000 Hz
Smooth
0.18
0.42
0.83
Double glazing, 2-3mm glass
Reflective
0.15
0.03
0.02
Patterned terrazzo tiles
Laid on concrete slab
Glossy
0.01
0.01
0.02
Exterior (Wall)
Fiberglass Panel absorbers
Fibreglass on frame,20mm cavity filled with rockwool
Soft fabric
0.15
0.75
0.8
Exterior (Wall)
Timber Wall
Acoustic timber veneer panelling
Smooth
0.18
0.42
0.83
Exterior (Flooring)
Carpeted Flooring
Medium pile Carpet on rubber underlay
Plushy
0.5
0.3
0.65
Interior (Wall)
Acoustic fabric
Timber Perforated Panel
Smooth
0.2
1.4
0.7
Soft
0.13
0.59
0.61
Plushy
0.5
0.3
0.65
Smooth
0.45
0.8
0.65
Interior (Seatings)
Fabric cushion
Interior (Flooring)
Carpeted Flooring
Interior (Ceiling)
Gypsum Plaster Ceiling
Upholstered Tip-up seats Medium pile Carpet on rubber underlay 17% perforated, 22mm
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AREA
MATERIAL PHOTO
SURFACE FINISHES
MATERIAL
DESCRIPTION
Entrance
Solid Timber Door
Timber Veneer Door
Stage (Wall)
Timber Perforated Acoustic Panels
Perforated Veneer Chipboard
COEFFICIENT 125 Hz
500 Hz
2000 Hz
Smooth
0.14
0.06
0.1
Laminated
0.41
0.58
0.68
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4.3
Acoustic Treatments & Components
Acoustic treatments and components are crucial for an auditorium as it affects the acoustic quality based on the function of the auditorium, in this case being a hall used for speeches, assemblies and public gathering. A standard acoustic treatment should meet conditions such as freedom from acoustical faults of echoes, flutter.
4.3.1
Wall panels
The walls are designed in a concave shape, a form that can be perceived as advantageous but disastrous at the same time. Disregarding that, the walls of the plenary hall are mostly covered with acoustical fabric installed with timber perforated acoustic panels and as well as timber framing. The back of the stage is covered with timber perforated acoustic walls.
Figure 4.3.1.1: location of acoustic panels on wall
Figure 4.3.1.2: Acoustic panels mounted on the wall of hall
Figure 4.3.1.3: timber frame and acoustical fabric
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4.3.1.1
Timber Perforated Acoustic Panel
Perforated panels are the most economical way to get an acoustic treatment with a high degree of absorption. It is applicable to walls and ceilings. For this auditorium, this timber perforated panels (Figure 4.3.1.6) are placed at the backdrop of stage to reduce reflected sound towards the speaker. Octagonal perforated panels (Figure 4.3.1.4) are used all around the wall. The panels used on timber walls let sound enter and then dissipate it, and the multitude of perforations allows air to pass through them so that the material can dissipate the sound waves as they collide against the walls of the cavity. Acoustic wool situated at the rear of the acoustic panel increases absorption for middle and high frequencies.
Figure 4.3.1.4: Octagon perforated acoustic panel on wall
Figure 4.3.1.6: Perforated acoustic panels as the backdrop of stage
Figure 4.3.1.5: Octagon perforated acoustic panel
Figure 4.3.1.7: Perforated acoustic panels
Timber perforated panel Air cavity Acoustic fabric Acoustic plasterboard Mineral wood insulation Barricade noise barrier Gypsum board Figure 4.3.1.8 Section detail of acoustic panel
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4.3.1.2
Acoustic Wall Panel
A sound diffuser is an acoustic panel used to treat sound aberrations, such as echoes and reflections, and to improve sound clarity. An ideal acoustic diffuser is a surface that causes an incident sound wave from any direction to be evenly scattered in all directions. The panels are arranged in a stepping configuration where it’s intention is to disperse sound waves in various direction. Based on our findings, we found that the acoustic panels are redundant based on the size of it againsts the scale of the hall. And is most likely used for aesthetic purposes to conceal the loudspeaker situated behind it, rather than serving acoustic purposes.
Figure 4.3.1.9: Sound diffuser panels, note the loudspeaker located behind the panels that suggests our findings.
Figure 4.3.1.10: Note the scale of the sound diffusers againsts the hall, only 2 are located in the hall.
Figure 4.3.1.11: Possible sound path directed to various direction
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4.3.2
Seating
There’s 3000 seats in this auditorium, each composed of a compact block of open-cell polyurethane foam that is attached to a 130mm thick beech plywood board. The seat automatically tips up as there is a double, lateral ball-and-socket joint system which requires no maintenance. The table is 54cm wide and 46cm deep, covered in leather. The seat, backrest and side panel assembly are joined together by a central steel bridge support attached to two aluminium side legs. The legs are joined to a lower steel plate base, through which the seat is attached to the floor with hidden metal expansion bolts. For long conference, the seating rows can alternatively be converted into large desk which automatically slide horizontally to allow access to and from the row, when a large working space is required. For short conference, all seats have an automatic folding anti-panic lectern.
Structure: - Steel tubing and plate; arc welded with continuous bead Polyurethane foam: - seat density: 60-65 kg/㎼ - backrest density: 50-55kg/㎼ Plywood: -Pressed beech plywood
Figure 4.3.2.1: Location of the seat in auditorium
Figure 4.3.2.2: Plenary configuration. Short time congress
Figure 4.3.2.4: overview of the seat from entrance
Figure 4.3.2.3: Parliament configuration. Long time congress
Figure 4.3.2.5: Side view of the seat
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4.3.3
Ceiling
Figure 4.3.3.1: Concave ceiling inspired by Mengkuang craft
The ceiling is installed with voids on the sides to allow the penetration of natural light into the auditorium. Concave ceiling is used in the auditorium to reflect the sound onto certain areas of the hall. This design may bring several disadvantages, it focus sound energy thereby creating hot spots and dead spots. Therefore, a concave ceiling should always be supported by the diffusing elements placed on wall in order for the sound to be dispersed in all directions.
Figure 4.3.3.2: Sound Reflection from concave ceiling to one certain area
Figure 4.3.3.3: Dead spots and hot spots created by concave ceiling
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Figure 4.3.3.4: Perforated Metal Ceiling Panels
The ceiling material used in the auditorium is perforated metal ceiling panels. This type of panels is commonly used nowadays due to its versatility. Not only it requires low maintenance, it is also able to aid in sound absorption, separating the noisy areas with a quieter surroundings. Perforated panels effectively reduce unwanted ambient noises by dispersing the sound waves on contact, making the sounds much clearer.
Figure 4.3.3.5: Layering details of Perforated Metal Ceiling Panels
The layer of mineral wool can absorb sound wave and act as a means of reverberation control. Therefore when sound waves hit the panels, they quickly dissipate, killing all the noise. Perforated panel absorber is actually a type of hybrid absorber, it is a cross in between membrane absorber and diaphragmatic absorber. Perforated panel absorber is almost equal in performance as membrane absorber, however it is not as low as diaphragmatic absorber. Perforated panel absorber have perforations on the front panel which help in allowing air movement in it. Diaphragmatic absorber on the other hand has no perforations but a solid panel. In comparison, diaphragmatic absorber has very limited ability in absorbing sound waves, the waves just bounce around noisily until they diffuse on their own.
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4.3.4
Flooring
4.3.4.1 Stage Flooring
Figure 4.3.4.1: Location of stage
Figure 4.3.4.2: Stage Flooring
The stage is constructed with hardwood as a hollow construction and possess a thin layer or carpet covering. The carpet acts as a sound absorber against noises from knocking and walking.
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4.3.4.2 Audience Flooring
Figure 4.3.4.3: Location of Carpeted Area
Figure 4.3.4.4: Carpeted Flooring
Figure 4.3.4.5: Layering details of Carpeted Floor
Majority of the floor in the auditorium is covered with carpet due to its ability as a good sound absorbing material. Carpet flooring prevents hard contacts with the floor, it can also be considered as a safer flooring because it is cushioned, thus less likely to produce injury if someone falls on it. Although carpet flooring does not help in sound transmission, it reduced sound impacts. Air is transmitted by vibration of air molecules, sound waves are absorbed instead of being reflected away back to the surface. The rubber layer underlay also helps in strengthening the sound absorption. These layers can effectively absorb sounds up to ten times better than normal hardwood flooring. Metal plates on the other hand are placed at the risers of staircase to reflect sound.
Figure 4.3.4.5: Comparison of different surface
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4.3.4.3. Sound Lock
Sound lock is an area usually designed to be between the lobby located between the hall and the waiting area that has high absorbant elements such as walls, ceilings and floors to help reduce transmission of noise into the auditorium. For PICC, the sound lock was seemingly effective as the scale of the sound lock area is huge enough and there are almost zero noise that can be heard in the hall even at the seats near the entrances
Figure 4.3.4.6.: shows the inner and outer door creating a sound lock from the waiting area, external sound from suites..
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4.4
Sound & Noise Sources
The term “sound” and “noise” are often interpreted to mean the the same, however, noise can only be subjected on the receiver point of view. In other words noise is any undesired sound considered by the listener/occupant. The level of undesiredness will depend on the various qualities such as frequency, loudness of the sound, time of occurrence, continuity, place, activity being carried out, origin of the sound and even the personal state of the listener.
4.4.1
External Noise
There are multiple origins of sound that can be found outside the auditorium, firstly the sound produced by the opening and closing of the door. The noise produced by the people talking outside can also be heard to a certain level but due to the sound lock created between the hall and the corridor.
Figure 4.4.1: shows the inner and outer door creating a sound lock from the waiting area, external sound from suites..
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4.4.1.1
Timber Perforated Acoustic Panel
The waiting area outside the hall is exposed by glass panels which causes environmental noises such as thundering. As a layer of corridor and guest waiting rooms create a buffer there is still chances of the noise to travel airborne.
Figure 4.4.2: shows exterior corridor that is exposed with glass which connects to the auditorium.
Certain areas in the hall’s exterior is also surrounded by suites for the members to wait in before function starts. On each door there are dampers applied to avoid banging to reduce structure borne transfer as the suits are parallel to the auditorium..
Figure 4.4.3: shows the inner corridor in between the suits and the hall. Doors and walking causes undesired noise.
The narrow corridor that is in between the hall and the suits can be seen separated by row of rooms to avoid noise from traveling to the stage area of the hall. Door dampers are present on each end, as well as carpets are laid on the flooring of the corridor. However the noise from the act of opening and closing itself causes noise due to its excessive weight.
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4.4.2
Internal Noise
As compared to external noises, internal noise sources are more prominent in the auditorium. Apart from the doors, there is a thudding sound created when one enters the hall, or is walking towards the stage or their respective seats. There was a “whoosh� noise that can be heard at the front and back from the air conditioners are turned on. The back of the auditorium where the M&E room is placed, contribute to a slight disturbance to occupants seated near the area. The air gap below the timber stage, which is used for amplifying the subwoofers also contribute to the noise of the footsteps.
Figure 4.4.4 top left and right: staircase layered with carpet along with stair nosing that causes noise. Figure 4.4.5 left: wooden folding seats that cause noise when pushed down.
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The air-conditioning diffuser system runs along the gaps of the suspended ceiling. Long, narrow strips, that force the the air-conditioning into the space. In comparison to the size of the hall the number of panels would take longer time to cool the space even when the temperature for the aircon is set low. Additional coolers are placed every corner of the hall that also contributes to noise.
Figure 4.4.6 top left and right: indicates the row of air conditioning diffusers along the ceiling panels.
Figure 4.4.7 top left and right: highlighting the additional coolers placement near the seats.
The above mentioned undesired and unnecessary sound contributed causes constant and steady noise that affects the quality of the event held in the auditorium also affecting to the sound readings on the front and back of the hall.
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The ceiling of the hall consists of skylight opening that brings in natural light to the area, along with external noise from weather induced source which causes disturbance.
Figure 4.4.8: shows the sectional view of the auditorium showing the origin of noise produced by the external noise entering from the ceiling and the walking footsteps or sudden movement of the seats.
Figure 4.4.9: The doors located around the sides of the auditorium also produce sudden and temporary noise disturbance to the audience seated. Stairs with nosing creates disturbance to the seats adjacent due to structure borne.
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4.5.1
Sound Concentration
The measurement of the Sound Intensity Level (SIL) was taken from the sound source on a fixed level of volume generated from our portable speaker and across the three octave levels of 125Hz, 500Hz and 2000Hz.
Figure 4.5.1.1. SIL Measurement location in PICC. Grid line as shown are for indication purposes. Grid A - is at a distance of 5m from the stage and each subsequent grid (B,C,D) is 20 metres apart.
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LOCATION
Sound Intensity Level (dB) 125Hz
500Hz
In the case of unassisted sound reinforcement and data collected, we were able to conclude the following:-
2000Hz
A1
52
70
78
A2
54
70
78
A3
53
72
80
A4
53
71
79
B1
41
52
65
B2
42
57
65
B3
42
55
68
B4
43
53
70
C1
32
52
63
C2
34
52
60
C3
35
54
61
C4
36
53
63
D1
30
44
56
D2
32
47
55
D3
31
48
57
D4
29
46
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I. Front seats (A) of the stage receives most sound due to it being closest and the low stage height (600m) reinforces the sound angle directed to the area. II. Row (C) and (B) receives a level more or less the same III. Row (D) is considered as a sound shadow area in regards to no usage of sound reinforcement. It is situated approximately 7.5 metres above the center stage. Our findings were mainly influenced by the large hall, and absorption materials situated across the hall, we were also able to conclude that even though that the hall is at such a large scale, the seating stretches just slightly beyond 140° and hence allowing sound to travel at the optimum angle during unassisted sound reinforcement. Despite that, the hall stretches too far away causing the rear rows around the area of Grid D to have minimal level of sound. It is noted that the interior ambient sound level is at an average of 26dB. It is also noted that we were able to identify the instance of the inverse-square law where every doubling of distance from the sound source, there would be a loss of 6dB. This data would help sound engineers to determine the ideal location for setting up loudspeakers for various events/function. Sound reinforcement has to be established for this auditorium due to the large scale and to compensate for the sound shadow area.
Figure 4.5.1.2. SIL Data collected indicating the levels across three octaves. The measurements taken are of average. We ensured a constant level of volume from our output loudspeaker as a unchangeable variable to ensure the accuracy of our findings.
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Figure 4.5.1.3. Sound reflection diagram.
The sound reflection in the multipurpose hall is greatly reduced by the heavy usage of sound absorbing elements such as the octagon perforated acoustic panel and acoustical fabric. Sound is also diffused in the multipurpose hall with the help of timber elements with uneven surface. However, the sound is more concentrated on the front row (Row A) due to the large volume of space and excessive use of absorbent materials.
Figure 4.5.1.4. Sound reflection diagram with materials.
The extensive usage of sound absorbing materials is to reduce the sound being reflected. The sound intensity level at the back (Row D) was recorded to be in softer dB readings hence causing a slight problem for speech.
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4.5.2
Sound Reflection
Figure 4.5.2.1. Sound propagation towards row A.
Sound reflection is lacking in row A but the the distance is short enough for direct sound to travel to the audience directly.
Figure 4.5.2.2. Sound propagation towards row B.
Due to the high ceiling the sound reflected from the ceiling is greatly weaken when returning to the audience.
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Figure 4.5.2.3. Sound propagation towards row C.
The reflective materials is insufficient hence sound is not well reflected to row C. However the huge volume space allows sound to travel through it.
Figure 4.5.2.4. Sound propagation towards row D.
The distance was too large for sound to travel directly or to reflect to row D.
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4.5.3
Sound Shadow
A sound shadow is a phenomenon caused by the absorption or obstruction of sound wave by an object in its path. The effect produced is perceived as a reduction in sound loudness from the listener’s position in conjunction with the sound source and it’s obstruction. The Plenary Hall suffers with a sound shadow area at the rear rows however is noticed as a minor issue and is normal due to the large scale of the hall. Sound can still be heard at the area however it is a minimal level. This problem exists only when there is no usage of sound reinforcement such as microphones and loudspeakers.
STAGE
Figure 4.5.3.1. Diagram indicating the sound shadow area
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4.5.4
Sound Echo and Delay
An echo is defined by the repetition of a source sound at a delayed time after hearing the sourced sound. Sound echo is also known as sound delay. By using the formula of , We are able to find out the estimated delay time of the sound waves at different points in the auditorium. Delay time, is measured in milliseconds (ms). For an auditorium catered for speech related events, a delay of 40ms would be considered an echo, whereas for. music it would be at 100ms
A. B. C. D. E.
(17m+16.7m-8.7m) /0.34 (20.3m+16.3m-16.6m) /0.34 (23.8m+15.2m-23.1m) /0.34 (27.6m+15.1m-31.7m) /0.34 (31.3m+13.8m-38.3m) /0.34
= 73.8ms = 58.82ms = 46.76ms = 32.35ms = 20ms
Figure 4.5.4.1. Diagram indicating the position where we collected our findings.
During our visit, we noticed the echo when we clapped at center stage and group members mentioning the echo when stood at different locations. Based on the data collected above, we were able to find evidence that reinforces the occurrence of the echo and our observation.
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4.5.5
Reverberation
Figure 4.5.5.1 Table for building component absorption
Calculation Acoustic panel Wall (timber) A = 4387m² a = 0.42 Aa = 1842.54
Occupants A = 3000 a = 0.46 Aa = 1380
Ceiling (Perforated Metal Panels) A = 4135m² a = 0.87 Aa = 3597.45 Audience flooring (carpet) A = 3803.5m² a = 0.49 Aa = 1863.72 Stage flooring (thin carpet) A = 331.5m² a = 0.08 Aa = 26.52 Seating (timber and fabric) A = 519m² a = 0.59 Aa = 306.21
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RT = 0.16V/A Where: RT = Reverberation Time V= Volume of the room (mÂł) A = Total Absorption of room surfaces
RT = 0.16(52173)/7713.18 = 1.08
Sound that is capable of being heard after the producing of sound had been ceased. Surface of the auditorium is one of the reason that affect whether the reverberation of sound disappear in a longer time or a shorter time. Angled ceiling or surface produce the reflection of sound, in the same time sound disappear in a longer time while ceiling and surface with less angled produce less reflection of sound yet disappear quickly.
Reverberation time for PICC is 1.08. This reverberation time is recommended for theatres which is 1.0-1.5 seconds which is suitable for the events and activities held in PICC. However, the reverberation time for the auditorium is slightly low due to the usage of absorbent materials. Design considerations should be taken care of to increase the reverberation time of PICC by replacing absorption materials with reflective materials.
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4.5.6
Acoustical Defects & Design Issues
Figure 4.5.6.2 Inefficiency reflective properties surface sectional diagram
Angled design would have a better sound reflection as the sound will reflect back to audience when hits on angled surface. One of the concern of PICC is that the design of the ceiling reflector doesn’t has much angled surface yet it causes lesser sound to reflect back towards the audience in its longer and bigger spaces. The design of this auditorium appear in concave ceiling therefore it happens that it focus sound energy thereby creating hot spots and dead spots. The lack of angled surface and the heavy usage of sound absorbing elements causes the reflection and reverberation of sound directly reduced.
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4.5.7
Plenary Hall as a “Multipurpose Auditorium�
Putrajaya International convention centre Plenary Hall auditorium is used as a multipurpose auditorium. This auditorium is used to accommodate events that involves with speeches such as seminars, graduation ceremony, lectures, and talks. However, events relating to music such as orchestra and singing are not encouraged due to the low reverberation time of the hall. The hall is fairly big as it is able to accommodate 3000 users. It is important for the auditorium to have less echoes to ensure the clarity of the speeches transmitted with no repetition of sounds which enables the audience to be able to grasp the speaker’s word clearly. The liberal use of absorbent materials plays a vital role in controlling and limiting the degree of sound reflection that occurs in the auditorium. Nevertheless, the usage of absorbent materials at a substantial rate has helped to reduce the reverberation time of the auditorium. This causes the sound to be in a monotonous manner, suitable for speeches unlike music hall where the priority is to have high reverberation time to ensure that the music is played in the correct tune and rhythm.
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5.
Conclusion
To conclude our analysis and case study, the Plenary Hall of P.I.C.C is an auditorium that is generally unsuited for musical performances without the usage of sound reinforcement system such as microphones, loudspeakers, & etc. Correspondingly, the auditorium naturally uses the system even for speech functions as the nature is to ensure that listeners has the best sound concentration at all available time. The exorbitant use absorbent materials provides an unsuitable venue for musical performances, and hence hardly any musical events are held here, and the management caters and targets for large speech-oriented events rather than promoting musical performances. It would be noted as well that the hall retains basic acoustic design and is at a very “surface” level. An in depth study and design should be made in order to further improve the acoustics in the hall. And as many architects and critique would say, it lacks “feel”. Furthermore, the Plenary Hall is the grandest hall that the Putrajaya International Convention Centre can offer There is no such thing as a perfect auditorium hall, in part because “good acoustics” is a variable change depending how the architect juggle between economic feasibility and design, and the ability to adapt and cater for those two aspect at the final decision to be made at the client’s approval. The final outcome and design would be a reflection of said condition.
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6.
References
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