SCHOOL OF ARCHITECTURE, BUILDING & DESIGN

Bachelor of Science (Honours) in Architecture

AUDITORIUM A CASE STUDY ON ACOUSTIC DESIGN

BUILDING SCIENCE (BLD 61303)

MAJLIS BANDARAYA SHAH ALAM AUDITORIUM

Prepared by:

Lee Yih (0318340) Low En Huey (0317889) Tan Jo Lynn (0318518)

Teo Hong Wei (0322990) Tiong Jia Min (0323763) Too Kean Hou (0319575) Wong Zhen Fai (0317890) Yan Wai Chun (0319626)

Tutor: Mr. Azim Sulaiman

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TABLE OF CONTENT

CHAPTER 1.0 INTRODUCTION

Section 1.1 Acoustic Design Introduction 4

Section 1.2 Case Study Project Brief 4

CHAPTER 2.0 LITERATURE REVIEW

Section 2.1 Sound Reflection 5

Section 2.2 Sound Absorption 6

Section 2.3 Direct and Indirect Sound Path 8

Section 2.4 Reverberation Time 9

CHAPTER 3.0 SITE INFORMATION

Section 3.1 Chosen Site Introduction 11

Section 3.2 Technical Drawings 14

Section 3.3 Site Zoning 16

CHAPTER 4.0 EXISTING SOUND SOURCES

Section 4.1 Sound Surround System 18

Section 4.2 Existing Noise Source and Noise Control 20

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CHAPTER 5.0 MATERIALS AND PROPERTIES 24

Section 5.1 Floor 26

Section 5.2 Wall 28

Section 5.3 Ceiling 29

Section 5.4 Seating 30

Section 5.5 Stage 30

Section 5.6 Openings 31

Section 5.7 Balcony 31

CHAPTER 6.0 SITE ACOUSTIC ANALYSIS

Section 6.1 Incident Sound 32

Section 6.2 Sound Reflection and Absorption 33

Section 6.3 Sound Diffusion / Dispersion 37

Section 6.4 Reverberation Time Calculation 40

CHAPTER 7.0 ISSUES AND RECOMMENDATIONS 42

CHAPTER 8.0 CONCLUSION 47

CHAPTER 9.0 APPENDIX AND REFERENCES 49

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CHAPTER 1.0 INTRODUCTION

1.1 Acoustic Design Introduction

Acoustic design is the use of architectural and engineering techniques to control the

behaviour of sound in an enclosed space (in this case an auditorium). The purpose is to improve

sound distribution in the enclosed space by enhancing the desired sound suited for the program.

Acoustic design also aims to eliminate noise and undesired sound that would negatively affect the

desirability of the sounds. For instance, specific measures will be taken to make speech more

intelligible or to make music sound better for the users. Building materials, architectural designs

and layouts will be taken into consideration while engaging in acoustic designs.

1.2 Case Study Project Brief

For this project, we were tasked to conduct our observational study and research on a local

auditorium. The research is based on the acoustic design elements applied by the designer of the

chosen auditorium. We were required to record our observations and analysis in a report format.

Our research will be broken down into several categories; common program and usage of the

auditorium, existing sound sources, materials used and how these factors affect the acoustic design

of the auditorium in terms of the sound path and its reverberation time.

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CHAPTER 2.0 LITERATURE REVIEW

2.1 Sound Reflection

When sound travels in a given medium, it strikes the surface of another medium and

bounces back in other directions, this phenomenon is called the reflection of sound. The waves are

called the incident and reflected sound waves. Different type of surfaces that contact with the sound

waves react differently, for instance, hard surfaces will reflect almost all of the incident sound

energy. Convex surfaces will disperse sound while concave surfaces will concentrate the reflected

sound.

Reflection of sound waves in auditoriums and concert halls do not always lead to

displeasing results, especially if the reflections are designed right. Reflection is often used as a

reinforcement of sound and to distribute the sound.

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Figure 2.1.1 Sound Reflection Diagram

2.2 Sound Absorption Coefficient

The absorption coefficient is a common quantity used for measuring the amount of sound

absorption of a material and is known to be the function of the frequency of the incident wave. It is

defined as the ratio of energy absorbed by a material to the energy incident upon its surface.

Absorption coefficient, α = Sound Energy Absorbed

Incident Sound Energy

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Figure 2.1.2 /useful ceiling reflections for flat ceiling.

Figure 2.1.3 Useful ceiling reflection for layered ceiling.

A perfect absorber has an absorption coefficient of 1.0, for instance, an open window. Sound

absorption coefficient performed differently with different type of building materials.

2.2.1 Types of Sound Absorber

1. Porous absorbers

Porous sound absorbers react to the materials in its network of interconnected pores and the

thermal interaction cause sound energy to be dissipated and converted to heat. The absorption of

porous material is most effective at frequencies above 1 kHz.

2. Cavity absorbers

Helmholtz Resonators or cavity absorbers are perforated structures containing very small

pores and connected by a narrow opening to the surrounding. It can absorb maximum sound energy

in a narrow region of a low frequency band.

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Figure 2.2.1.1 Examples of porous absorbers.

Figure 2.2.1.2 Examples of Cavity Absorbers.

2.3 Direct and Indirect Sound Path

The sound emitted from the sound source that reaches the audience without any reflection is

called direct sound; the sound that reaches the audience after one or more reflections is called

indirect sound. When the audience in a hall or acoustic room is seated closely with the main stage,

they tend to receive direct sound more whereas the audience seated further away often receives

indirect or reflected sound.

Indirect sound have widely varying reflective properties compared to direct sound as they

reflect on different surfaces or distances in the hall/acoustic room. Reflected sound beneficially

reinforces the direct sound if the time delay between them is relatively short, that is a maximum of

30msec.

Time Delay = 𝑅1+𝑅2 –𝐷

0.34

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Figure 2.3.1 Reflection of direct sound path.

2.4 Reverberation Time

Reverberation is the continuing presence of audible sound after the producing of sound has

been stopped. It is affected by the reflective properties of the surfaces in the hall or acoustic room. A

reflective surface will cause the sound to die away in a longer period of time while an absorbance

surface will cause the sound to die away quickly.

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Figure 2.3.2 Sound reflector diagram.

Figure 2.4.1 Reverberation time diagram.

If the source of sound stops, in a result, the reverberant sound level decays (loses sound

pressure level over some time). Besides, the time it takes for sound pressure level to decay will

affect the acoustical quality of the space.

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 is dependent upon a few factors, the volume of

the enclosure (distance), total surface area, and the absorption coefficients of the surfaces.

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Figure 2.4.2 Reverberation time diagram.

CHAPTER 3.0 SITE INFORMATION

3.1 Chosen Site Information

The Majlis Bandaraya Shah Alam auditorium was built in the early 90s and could

accommodate approximately 1000 people. During the early years, the auditorium was mainly used

for formal events where foreign diplomats were usually involved hence there were several

translation rooms overlooking the auditorium from above. It was also the favoured venue to

perform for the Malaysian Philharmonic Orchestra before the Petronas Filharmonik Hall was built

in 1998. A season of the Malaysian TV reality show “Maharaja Lawak Mega” was aired live from

the auditorium. The typical programmes in the auditorium are live singing performances and

occasionally some formal speeches. The in-house sound system has been out of order since 2014

and there were no restoration efforts scheduled due to lack of funding and the outdated nature of the

sound systems.

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Figure 3.1.1 Live concert performances

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Figure 3.1.2 Live concert performances.

Figure 3.1.3 Formal speech event.

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Figure 3.1.4 Perspectives of the auditorium hall.

3.2 Auditorium’s Drawings

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Figure 3.2.1 Lower Ground Floor Plan.

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Figure 3.2.2 Upper Ground Floor Plan.

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Figure 3.2.3 Longitudinal Section.

3.3 Site Zoning

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Figure 3.3.1 Lower level sound intensity.

Figure 3.3.2 Upper level sound intensity.

CHAPTER 4.0 EXISTING SOUND SOURCES

4.1 Sound Surround System

The MBSA Auditorium Hall uses the 5.1 surround sound system since the completion of the

hall in the early 90s. This surround sound system often indicates to system of a high standard

quality, as ‘true’ surround sound. The system consists of five speakers and a subwoofer; a powered

power designed to produce bass tones and low frequency tones. As for the main five speakers, two

of them are on the front left and right, and two are at the rear left and right, and lastly the center

quality speaker. The center speaker system is larger and more versatile, where it consists of more

individual speaker cones.

4.1.1 Equipment Location

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Figure 4.1.1 Ground Floor Plan

4.1.2 Equipment Specification

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Figure 4.1.2 First Floor Floor Plan

4.2 Existing Noise Source and Noise Control

4.2.1 External Noise

In the MBSA Auditorium Hall, the absence of external noise source could be

detected due to the existence of soundproof system and the location of the building, which is

further away from other surrounding buildings. It is also enabled by the spaces placed

around the auditorium hall, which forms a buffer zone, enhancing the desire sound in the

auditorium.

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Figure 4.2.1.1 External noise source location and buffer zone indication

4.2.2 Internal Noise

The internal noise source locates around the auditorium hall, which is the corridor

direct towards the entrance as well as the backstage area. This noise source exists only

during the presents of events. It is reduced by the application of soundproof wall around the

auditorium space. Internal noise source also comes from the ceiling air grills installed

throughout the lower floor ceiling for ventilation and air conditioning purposes. It is avoided

by the management group through activating the ventilation system 1 to 2 hours ahead of the

event at low-level to prevent the noise from degrading the standard of performance.

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Figure 4.2.2.1 Internal noise sources’ location

4.2.3 Equipment Specification

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CHAPTER 5.0 MATERIALS AND PROPERTIES

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Figure 5.1 Materials’ location

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Figure 5.2 Materials’ location

Material Absorption Coefficient

5.1 Floor

Wood flooring is any product manufactured from timber that is designed for use as flooring,

either structural or aesthetic purpose. This type of flooring is generally used for special purpose

floor, like the auditorium due to its reflective nature.

Wood is a common choice as a flooring material and can come in various styles. The type of

wood flooring used in MBSA Auditorium is solid hardwood flooring.

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Solid hardwood floors are made of planks milled from a single piece of timber. Solid wood

floors have a thicker wear surface and can be sanded and finished more times than an engineered

wood floor.

A sloping floor is desirable especially for large halls, it helps in improving the sight lines of

the audience. Moreover, when sitting on a sloping floor, the listeners receives more direct sound

compared to when it is on a flat floor.

Generally, the slope of an auditorium floor should not be less than 8° and for safety purposes

the slope should not exceed about 35°.

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Figure 5.1.1 Materials used at different location.

5.2 Wall

5.2 Wall

The walls of the auditorium are generally covered with sound absorbent materials like

compressed fibreboard or draperies, which is to reduce reverberation. These materials reduce the

formation of echoes by absorbing sound waves.

The acoustic material typically visible to the audience is devoted to a different task

altogether: absorbing or dampening the sound waves that emanate from stage in front of them. Most

of the time, the idea behind the application of these materials is to keep the sounds from echoing off

of the walls of an enclosed space, a phenomenon that, if left unchecked, would likely produce a

very aurally confusing experience for the audience.

The type of material used on the walls in MBSA Auditorium is sound absorbing foam. It is

layered on with wooden panels of different widths that act as a diffuser, which is to match the high

and low frequencies of sound.

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Figure 5.1.2 Floor slope diagram.

5.3 Ceiling

The ceiling of MBSA has a slanting profile to reflect the sound. It is suspended plaster,

providing different planes that reflect varying wavelengths of sound. Constructed on metal lath, the

ceiling is plastered thickly to resist panel vibration. Also with the thick mass of plaster and a proper

suspension system, it will permit the external noise from being transferred inside. A high volume of

the auditorium hall is recommended for good acoustic qualities.

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Figure 5.2.1 Photo of absorptive wall.

Figure 5.3.1 Photo of auditorium’s ceiling.

5.4 Seating

The total seating capacity of the auditorium is 1237. They are arranged in ¾ arena form that

enables 180-270 degree angle of inclusion. All seats are fixed and upholstered with moulded metal

support at the leg. The front of the chairs are covered with fabric which is sound absorbing whereas

the back of the seat pans are perforated metal over sound absorbing material. This is to ensure that

the absence and presence of audience does not affect the reverberation time. When the seats are

occupied, the absorption effect is reduced as it faces the floor whereas when unoccupied it faces the

stage.

5.5 Stage

The stage is divided into 3 parts, with one fixed central stage and 2 fore-stage platforms. The

fore-stage platform can be adjusted from 0.00m to +1.00m depending on the function of the event.

The space beneath the stage is hollow so sound will travel through the flooring and empty space to

be reflected by the concrete base at the bottom. When the sound is reflected back to the surface of

the flooring, the intensity of the sound would have been reduced. Hardwood timber flooring is used

for the stage.

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Figure 5.4.1 Customised seating diagram.

5.6 Openings

There are total of 7 fire exit doors in the auditorium. 4 doors are located at ground floor and

the rest at second floor. The wooden doors are acoustic and framed with steel. All of the doors have

thick curtain hung against them. The curtains act as sound absorber so that when the door is opened,

the sound will not escape from the hall. It also covers the reflective surface of the door.

5.7 Balcony

There are two balconies on each side of the wing. The balconies have fixed seats for the VIP

and carpeted flooring. Plasterboard is used for the ceiling. The railings protecting the audience from

falling off from the balcony are wooden bars and thick clear acrylic panels. The panels are made

thick to resist panel vibration.

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Figure 5.5.1 Perspective of stage.

CHAPTER 6.0 SITE ACOUSTICAL ANALYSIS

6.1 Incident Sound

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Audience sitting at the front row receives higher intensity of direct sound from the sound source compared to other positions in the hall.

Audience sitting at the middle row will receive relatively lower sound intensity as it is further from the sound source.

The intensity of sound decreases as the distance from the sound source increases. Therefore, audience sits at the upper level receives the lowest intensity of direct sound.

Audience at underside of the deep balcony are in the potential sound shadow area, where direct sound could not reach. Sound reflection and diffraction are used to supplement for the condition.

Figure 6.1.1 Incident sound diagram.

6.2 Sound Reflection and Absorption

6.2.1 Properly-tilted Ceiling

Back rows of audience seatings are shaded with lower ceiling resulting from balcony

seatings at upper level. Slanted ceiling reflects sound and distribute it to deeper rows of seatings to

optimise the acoustic experience.

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Figure 6.2.1.1 Sound Reflection Analysis of Rear of Auditorium.

Figure 6.2.1.2 Sound Reflection Analysis of Ceiling of Auditorium.

Properly tilted ceilings ensure the sound emitted from the sound source travel to the

audience by sound reflection and directs the sound in specific directions. As a result, reflection of

sound through the tilted ceiling is able to optimise and distribute sound throughout the whole

auditorium.

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Figure 6.2.1.3 Sound Reflection Analysis of In House Speakers.

6.2.2 Speakers

1. In house speakers

House speakers placed at stage acting as the main source of sound, directing all

incident sound towards audience, whereas sound woofers placed around audience provides

better hearing experience.

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Figure 6.2.2.1 Sound Reflection Analysis of External Speakers.

2. External Speakers

Two main speakers are placed on both sides of stage, where diamond shaped stage allows all

sound to be reflected towards audience, whereas monitor speakers direct sound to performers.

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Figure 6.2.2.2 Sound Reflection Analysis without Speakers

6.3 Sound Diffusion / Dispersion

By enhancing the sound emitted from sound source through the design and material of

surfaces it selves, usage of external amplifier is at zero. At lower level of auditorium, seatings at

centre row are removed due to the lack of reflected sound or weak reflected sound arriving at that

position, as two straight walls are placed parallel to each other, perpendicular to sound source.

Control Room with Angular Surfaces

Above the box seatings is an angular surface that reflects the sound emitted from sound

source. Sides of the surface are made up of wooden panels, in a result, the audience receives

adequate amount of reflected sound from the surrounding area.

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Figure 6.3.1 Sound Reflection Analysis of Angular Surfaces.

Acoustic Shadow

The deep balcony created a potential acoustical shadow at the seats underneath the

balcony. Besides that, the application of absorptive wall at the end of the auditorium hall

causes the possible reflected sound waves to lose its energy, therefore transmitting a

relatively low intensity reflected sound towards the area below, forming an acoustic shadow

area.

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Figure 6.3.2 Acoustic Shadow

Figure 6.3.3 Interior Side View Figure 6.3.4 Removal of Seats

Wooden Slat Acoustic Diffuser

The wooden slats acoustic diffuser applied on the wall functions with the same theory as

cavity absorber. When sound waves travel into the gap space, certain percentage of it is absorbed by

the absorption material behind the slats, the reduced sound energy is then reflected for multiple

times in the space, further decreasing the energy of sound.

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Figure 6.3.5 Sound Reflection in Cavity Wall.

6.4 Reverberation Time Calculation

Absorption of surface = Surface area (m²) x Absorption coefficient of surface (500Hz)

As (Ceiling) = 630.7m² x 0.1 = 63.07 m²sabins

As (Seating) = 1.2m² x 1237 x 0.56 = 831.26 m²sabins

As (Curtain) = 45.5m² x 0.35 = 15.93 m²sabins

Wall

As (Wood Slat Acoustic Diffuser) = 102.3m² x 0.42 = 42.97 m²sabins

As (Wood Panel Sound Diffuser) = 232.66m² x 0.17 = 39.55 m²sabins

As (Concrete) = 697.33m² x 0.02 = 13.95 m²sabins

Floor

As (Carpet) = 352.72m² x 0.44 = 49.38 m²sabins

As (Wooden) = 281.12m² x 0.2 = 56.22 m²sabins

As (Door) = 65m² x 0.14 = 9.1 m²sabins

Balcony

As (Thick Clear Acrylic Panels) = 32.36m² x 0.7 = 22.65 m²sabins

As (Wood Railing) = 16.95m² x 0.1 = 1.7 m²sabins

Openings

As (Deep Balcony) = 110.4² x 0.5 = 55.2 m²sabins

As (Ventilation Grills) = 2.97m² x 0.15 = 0.45 m²sabins

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Total Absorption = 63.07 + 831.26 + 15.93 + 42.97 + 39.55 + 13.95 + 49.38 + 56.22 + 9.1 + 22.65 + 1.7 + 55.2 + 0.45 = 1201.43 (m²sabins)

Reverberation Time = 0.16 x Volume of the room ÷ Total absorption

RT = 0.16 x 10200m³ ÷ 1201.43m²sabins = 1.36s

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CHAPTER 7.0 ISSUE AND RECOMMENDATION

7.1 Issues

One of the concerns that could be seen in MBSA auditorium hall is the absence of concave

surface that has the potential to form concentration of sound waves especially for the back rows.

This will result in non-uniform distribution of sound waves, causing a different acoustic experience

for the audience.

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Figure 7.1.1 Sound Reflection of Auditorium.

Another issue that is detected in the hall is the acoustic shadow area that is located below the

balcony due to the depth as well as the absorptive wall behind. This could affect the amount of

sound received by audience, especially the last seating row.

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Figure 7.1.2 Sound Shadow Issue

7.2 Recommendations

Solution 01

To achieve desired sound throughout the whole auditorium and to ensure the satisfaction of

the acoustic experience, ceiling is recommend to tilt or orientate in a more concave-like shape.

Concentrated sound can be produced and distributed uniformly once the sound is reflected.

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Figure 7.2.1 Concave Ceiling Suggestion.

Solution 02

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Figure 7.2.2 Ceiling Adjustment.

The initial design of the auditorium hall has a deep balcony, which then creates a potential

acoustical shadow underneath the balcony. The application of absorptive wall at the end of the

auditorium hall also causes the possible reflected sound to losses its energy, therefore transmitting a

relatively low intensity sound towards the area, forming an acoustic shadow area.

The recommended solution for the occurrence of acoustic shadow below the balcony is to escalate

the height of the floor to balcony dimension and at the same time, increase the steepness of the

tilted ceiling of the lower floor. This will ensure the reflected sound is able to be guided towards the

audience below the balcony area without decreasing the energy of the sound.

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CHAPTER 8.0 CONCLUSION The calculated reverberation time of 1.36s at 10200m³ volume reinforces the mixed use

nature of the Majlis Bandaraya Shah Alam auditorium. With the common programs such as live

singing performances and the occasional speech conferences, the reverberation time is neutral and

neither fully catered towards speeches nor musicals. The reverberation time of 1.36s is suitable for

live singing performances due to the presence of music that should have a relatively higher

reverberation time to reach more ‘fullness’ and at the same time, the program requires a relatively

lower reverberation time to maintain the intelligibility of the lyrics.

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CHAPTER 9.0 APPENDIX AND REFERENCES

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REFERECNES

1. https://www.acousticalsurfaces.com/acoustic_IOI/101_13.htm

2. https://www.barbourproductsearch.info/DeAmp%20Brochure-file058984.pdf

3. http://www.acoustic.ua/st/web_absorption_data_eng.pdf

4. http://mapleintegration.com/sound_ab.php

5. https://issuu.com/jacquelyntan/docs/a4_report_completed

6. https://www.engr.psu.edu/ae/thesis/portfolios/2005/sas444/Final%20Report/Acoustics.pdf

7. https://www.omicsonline.org/open-access/a-comparative-analysis-of-acoustic-material-and-

effects-on-churchauditoriums-old-and-new-churches-in-nigeria-0976-4860-1000153.php?

aid=67941

8. https://www.lifewire.com/what-is-surround-sound-audio-2640440

9. http://www.electrovoice.com/downloads.php?fam=51&title=SL%20Series&d=1

10. http://www.hifido.co.jp/KW/G0201/J/0-10/C12-68892-54803-00/

11. http://www.music-group.com/Categories/Behringer/Loudspeaker-Systems/Portable-

Speakers/B1220-PRO/p/P0284

12. https://oneroofstore.com/behringer-vp1520.html

13. https://www.bunnings.com.au/csr-edmonds-ventilation-whirly-mate-ceiling-grille_p0816657

14. https://issuu.com/priscakwan/docs/toc.docx

15. https://www.slideshare.net/mominzaki/auditorium-acoustics-33230112

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