Building Science II Project 1 - Acoustic Design

School of Architecture, Building and Design
Bachelor of Science (Hons) in Architecture
Building Science I
Project 1
Auditorium: A Case Study on Acoustic Design
Group Members:
Ahmad Ashraf 0317744
Aidan Ho Wei Suan 0326021
Caleb Soh Er Wen 0320292
Hor Ming Jack 0325145
Jack Lee Hor Kit 0325810
Ng Wyn Jane 0319440
Nik Munawwar Nik Din 0325167
Thareen Nujjoo 0324886
Tutor:
Mr. Azim

A Case Study on Acoustic Design: Damansara Utama Methodist Church (DUMC)
TABLE OF CONTENTS
1. Introduction
1.1 Aims & Objectives 2
1.2 Site 3
1.3 Drawings 4
2. Acoustic Theory
2.1 Acoustics in Architecture 5
2.2 Sound Intensity Level 5
2.3 Reverberation, Attenuation, Echoes, and Sound Shadows 5
2.5 Acoustic Design for Auditoriums 6
3. Methodology
3.1 Equipment 7
3.2 Data Collection Method 9
4. Acoustic Analysis
4.1 Auditorium Design 11
4.2 Materials 18
4.3 Acoustic Treatments & Components 20
4.4 Sound & Noise Sources 29
4.5 Sound Propagations and Related Phenomena 41
5. Observation, Discussions and Conclusion 50
6. References 51
1

1. Introduction
1.1 Aims & Objectives
The aim of this report is to document the research conducted on the acoustical
design of an auditorium in order to provide an insight into the intricacies of
acoustic modeling, design and implementation. The objectives of the report are
as follows:
1. To conduct an in-depth exploration of the auditorium typology based on its
layout, designed with an intention for a specific acoustic performance
according to the needs of its functions.
2. To develop a robust understanding of the physics behind the acoustic
quality of an auditorium.
3. To analyse the relationship between acoustics and the materials, spatial
planning and context of an auditorium.
2

1.2 Site
1.2.1 Basic Information
Name of Auditorium : Damansara Utama Methodist Church (DUMC)
Location : Seksyen 13, 46200 Petaling Jaya, Selangor,
Malaysia
Type of Auditorium : Multi-purpose auditorium
Year of Construction : 2005
Year of Completion : 2007
Total Volume : 18655m3
Total Seat : 2301 seats
1.2.2 Historical Background
Damansara Utama Methodist Church (DUMC) was started in 1980 by a group of
22 professionals and 3 children from SSMC (Sungai Way-Subang Methodist
Church). They started of in a shop lot premise in Damansara Uptown before
moving to a factory lot in Taman Mayang in 1993 to accommodate the fast
growing congregation which at this point had reached 500 people.
The Chinese congregation was started in 1996 as the first vernacular service in
DUMC. At the same time, to accommodate the growing size of the congregation,
more services were held each weekend. By 1998, they were having three
celebrations weekly with a congregation size of 1000 worshippers.
The numbers continue to grow until 2007 when they moved to the current
premise - Dream Centre. At present time, the congregation stands at 4500
worshippers weekly across seven different vernacular services.
3

1.3 Drawings
Ground Floor Plan
First Floor Plan
4

2. Acoustic Theory
2.1 Acoustics in Architecture
Acoustic architecture, is a field of study that dabbles on the nature of sound and its
manipulation within the space allotted to it.
Be it an open amphitheatre or a fully indoor auditorium, acoustic architecture attempts
to optimize the sound quality for whatever activities it houses
2.2 Sound Intensity Level
Sound intensity is defined as the sound power per unit area (watts/m2
)
2.3 Reverberation, Attenuation, Echoes and Sound Shadows
Reverberation - Persistence of sound after a sound is produced. A measure of sound
decay through its propagation, ie flutter echoes.
5

Attenuation - Nature/Energy level of sound as it propagates through mediums of
different density and scatters to the surrounding environment.
α= Energy Absorbed / Incident Energy
Echoes - Sound reflection is as ubiquitous as the cosmic radiation that
surrounds us always. Echoes are defined as sound reflections that
is returned to the listener with a perceptible magnitude. Multiple
echoes create Reverberations.
D=VT
Sound Shadows - Areas that are shielded from sound waves through mediums that
either absorb or reflect such waves to a considerable degree.
2.4 Acoustic Design for Auditoriums
Goals:
a) Preservation of sound intensity (longer the better)
b) Clarity in sound delivery
c) Optimum reverberation time
d) Prevent excessive vibrations
e) Reasonably reduce external noise
6

3. Methodology
3.1 Equipment
3.1.1 Digital Sound Level Meter
3.1.2 Digital Camera
3.1.3 Measuring Devices
- Measuring Tape, Laser Distance Measurer
7

3.1.4 Source generator
● Bluetooth speaker + Tripod
Specifications:
Max. Power Output: 3W
Bluetooth Transmission Distance: 10m
Bluetooth Version: 3.0 Class II, Support A2DP V1.2, AVRCP V1.4 profiles
Audio Input Interface: 3.5mm audio interface, support AUX external audio input
Tripod height : 1.6m
● Tone generator (phone app)
Specifications:
Frequency range : 0hz - 20000hz
Tested frequency : 125hz, 500hz, 2000hz
3.1.5 Human
8

3.2 Data Collection Method
Measuring Dimensions
● Long measuring roll tape - for short and easily accessible areas up to 9m
● Laser distance measurer - for long inaccessible areas ie ceiling height
Measuring Sound Intensity Levels
● Set bluetooth speaker at the center of the stage at 1.6m height from stage floor
● Take a controlled sound level at 1m away from sound source at
(125hz,500hz,2000hz)
● Take sample at 5 m away from sound source at (125hz,500hz,2000hz0
● Repeat sample taking at multiples of 5m including backstage
9

Measuring Sound Attenuation (in children's play area)
● Set bluetooth speaker inside the children play area at 1.6m height from floor
● Set sound source and receiver at 2m away from the glass panels
● Take sample of noise level through the glass pane
10

4. Acoustic Analysis
4.1 Auditorium Design
4.1.1 Shape of Auditorium
The auditorium is designed as a fan shape. This configuration results in a more intimate
space as the audiences are brought closer to the speaker. Due to the closer proximity
between the audiences and the speaker, the sound of the speaker is louder and more
audible, which in turn improves the listening condition for the audience. This
arrangement also creates a central focus which further contributes to a more intimate
relationship between the speaker and the audience.
However, the arrangement of the auditorium, which is at 150°, exceeds the maximum
limit of 130° for a wide fan arrangement. This affects the audience situated beyond the
suggested limit who will have to put up with a poor listening condition. Ideally, there
should be no seats beyond the maximum limit for the fan shaped arrangement as it
severely affects the listening condition of the audience.
The figure denotes the region which is within the 130° limit.
Note the seating on both sides which fall outside this region.
11

4.1.2 Levelling of Seats
The leveling of the seating area is of utmost importance to ensure that sound waves
reach the ears of all occupants within the auditorium clearly. There are two types of seat
in the auditorium which are fixed and movable seats to accommodate different occasion
use. The fixed seats are placed at level terrace on the ground floor and first floor, while
the movable seats are placed at the ground floor pit.
The figures above show the seat arrangement at ground floor pit, ground floor terrace and first floor terrace.

12

At the ground floor pit, the sound attenuation is not resolved due to the seats that are
located at the same level. The intensity of sound is decreased over time to reach the
furthermost seat as the sound is absorbed in part by the seats in the first half.
The seat arrangement at ground floor pit which arranged in the same level.
The seats at the terrace on the ground floor are elevated from the ground floor pit but
are not evenly allocated because there are two consecutive rows of seat positioned at
the same level. With a same level positioned of seats, the propagation of sound source
is reflected and diffracted by the first row seats which caused uneven distribution of
sound that lead to the occurrence of undesirable acoustical defects.
The elevated seat arrangement at ground floor terrace.

13

The terrace seats at the first floor are in the most effective arrangement as they are
arranged in a staggered manner. Adequate sound diffusion is achieved to promote
uniform distribution of sound and accentuates the natural qualities of music and speech.
There is also no sound diffraction as there are no barriers such as corners, columns,
walls and beams in their path which provides an effectiveness of sound waves reaching
the ear of occupants without any objects blocking or absorbing it.
The seat arrangement at first floor terrace arranged in a staggered manner.
14

4.1.3 Arrangement of Seats
There are a total number of 2200 seats within the auditorium and they are arranged in a
fan shaped configuration. This arrangement is to achieve uniform quality sound over the
entire seating area because sound propagates outwards from the stage in a spherical
wave front. However, some of the seats are arranged beyond the maximum limit of the
fan shaped configuration which is 150 degree. A poor listening condition may occurred
throughout the acoustic experience for the audience situated beyond the suggested limit
seating arrangement.
The figure above shows the fan shaped configuration of seats within 150 ° sound projection angle.
15

4.1.4 Ceiling Design
The staggered ceiling configuration accommodates the inclusion of catwalks for easy
access to the spotlight gantries but more importantly, it serves to contribute useful
sound reflection towards the seating area, increasing the volume of the sound as it
reaches the audience. The concave design of the ceiling panels further aids to direct the
reflected sound waves back to the audience especially those seated at the gallery as
well as the rear of the ground floor. Ultimately, the ceiling panels serve the function as a
sound reflector to ensure that sound waves are distributed evenly throughout the
auditorium.
The staggered ceiling helps to reflect and distribute the sound waves evenly to the back section seating in the
gallery and ground floor.
16

4.1.5 Sound Shadow Area
A sound shadow area is defined as an area which sound waves fail to propagate to. In
the case of this auditorium, due to the position of the gallery, a sound shadow area is
formed at the back section of the ground floor sitting. The gallery shrouds the people
seated in this area from the sound waves produced from the house speaker arrays.
Fortunately, the sound shadow area in this auditorium is considered to be a minor issue
as it is shallow. Sound waves are still propagated to the ground floor seating via
reflection of the staggered ceiling panels hence no periphery audio devices are required
at the back section of the ground floor to compensate for the lost of sound quality via
the overhead house speakers.
The region under the gallery (highlighted in red) represents the shallow sound shadow area.
17

4.2 Material Table
AREA COMPO-
NENT
MATERIALS SURFACE
FINISHES
COEFFICIENT
MATERIAL DESCRIPTION 125
Hz
500
Hz
2000
Hz
Stage Walls 1. Concrete wall.
2. Canvas
background.
1. Smooth painted
concrete, 150mm
thick.
2. Thin tensile
canvas backdrop.
Paint. 0.01 0.01 0.02
Apron
Absorber
Carpet. 5mm thick needle
punch carpet.
0.03 0.05 0.35
Curtain Heavy Cloth. Medium velour,
50% gather, over
solid backing.
0.05 0.40 0.60
Flooring Timber parquet. Wooden platform
with large space
beneath it.
Polish. 0.40 0.20 0.15
Furniture Stage set and
instruments.
Proscenium
opening with
average stage set.
0.20 0.30 0.40
Flytower Steel. Steel joists/
framing.
House Walls 1. Drywall.
2. Timber.
3. Foam.
1.Plasterboard on
25mm battens.
2. Acoustic timber
wall panelling.
3. 25mm thick
foam covered by
scrim cloth on
solid plywood
backing.
Paint.
Polish.
0.31
0.18
0.90
0.14
0.42
0.54
0.10
0.83
0.88
Flooring Carpet. 5mm thick needle
punch carpet.
0.03 0.05 0.35
Seating 1. Padded chairs.
2. Auditorium
seats.
1. Padded chairs
with metal frame.
2. Thick cushion
seats.
0.08
0.13
0.15
0.59
0.18
0.61
Hand
Railing
1. Steel. 1. Painted steel
railing with steel
cables.
Paint.
18

2. Perspex. 2. Transparent
perspex panels.
Doors Timber. 1. Solid timber
double door.
2.Wood hollow
core door.
Paint.
Paint.
0.14
0.30
0.06
0.15
0.10
0.10
Ceiling 1. Plaster
2. Gypsum Plaster.
1. Plaster on laths
with airspace.
2. Gypsum plaster
tiles,
un-perforated with
airspace.
Plaster.
Plaster.
0.30
0.45
0.10
0.80
0.04
0.65
Control
Room
Glass. 4mm thick
window.
0.30 0.10 0.05

Padded Seat Curtains Acoustic Walls

Acoustic Timber Panel Carpet Gypsum Plaster

Acoustic Panels Plaster Concrete
19

4.3 Acoustic Treatments & Components
4.3.1 Wall Panels
1. Acoustic Foam Panels
The walls of the gallery of the DUMC auditorium are lined with acoustic panels of
different sizes and inclined at different angles. These are designed to prevent sound,
more specifically midrange and treble tones from hitting a solid surface and bouncing
back to the stage and create echos, by absorbing the sound energy through the
material.
20

The panels are made up of foam placed on a plywood surface and wrapped with fabric.
Since foam and textiles are porous materials, they easily absorb sound once it hits the
acoustic panel.
The top half of the foam acoustic panels are inclined at certain angles, creating a cavity
between the solid wall and the plywood sheet, which makes it more effective.
21


http://www.troldtekt.com/Product-properties/Good-acoustics/Acoustics-for-advanced/Different-absorber-types
2. Acoustic Timber Panels

http://www.stil-acoustics.co.uk/Timber-Acoustic/Linear.html
The lower half of the ground floor walls, are cladded with acoustic timber panels for
absorption of low frequency sounds.
Groove panels are cavity absorbers, they act as a perforated panel by absorbing sound
through the linear slits on the face of the panel, which are connected to large cutouts in
the back. A layer of mineral fibre is provided behind the panel in order to dampen the
sound energy, while a cavity between the wall and the panel creates resonance due to
air vibration. These, combined to the perforations create a Helmholtz absorber.
22

Alterations in acoustic performance are made possible by changing the distance
between the grooves or the perforation pattern, the cavity depth and the choice of
absorbent material. Smaller groove width usually increases acoustic performance.
3. Padded Walls

The rear walls of the auditorium are covered in a layer of foam and fabric. These walls
act as sound absorbers due to the porosity of the materials, to prevent reflection of
sound waves back toward the stage which is echo.
The padded walls are also located on the balcony strip, which is where the air
conditioning diffusers are. This is an attempt to absorb and dampen the sound caused
by the diffusers.
4. Dry Walls
Dry walls are located on the sides of the stage, being hard surfaces, they have very low
absorption abilities and are used to reflect sound coming from the stage back to the
audience.
In order to prevent any flutter that could occur during sound reflection, walls parallel to
the dry walls are avoided.
23

4.3.2 Flooring
Carpeted Floor
Majority of the floor in the Dream Centre auditorium is covered in a layer of carpet. The
needle punched carpet that is utilised is created by having barbed needles punched into
a matted layer of fiber, that form a mat of surface fibre.
This carpeting is sound absorbent, dampening impact and sounds that are a result of
the dense foot traffic. It is also porous and absorbs sound energy and reduces
reflections and echoes.
24

Between the carpet and the existing concrete floor, a thin floor underlayment is used to
provide further cushioning from footsteps and impacts, and prevent the transmission of
floor vibrations. The underlayment is comprised of 2 layers, a flexible solid mass barrier,
a soft foam portion that prevents the vibrations and is to be faced toward the ground.
4.3.3 Curtains
Velour Curtains
These are heavy sound-absorbing curtains that are located in strategic locations of the
auditorium in order to dampen sound efficiently. Curtains are located at 2 types of
areas; At entry points to the auditorium and at the stage.
25


Curtains are found at access points in order to diminish sounds coming from the
opening and closing of doors as people walk in and out of the auditorium, and also to
stop sound from escaping the space and leaking into the external area.
At the stage, curtains serve the purpose of aesthetics & concealment, as well as to
reduce the reflection of sound, and ultimately echoes. These curtains also stop sound
that is made backstage from being heard in the auditorium.
However, to naturally propagate sound more efficiently and effectively, the backdrop
curtain of the stage should be removed, and replaced with a more acoustically reflective
in order for sound to bounce of it and back to the audience.
4.3.4 Seating
26

Padded Theatre Seating
The auditorium feature 2 styles of seating, fixed folding theatre seating at the back of
the auditorium and movable seating at front.
The seating and audience of an auditorium are usually the main points of sound
absorption in the room. Because of this, it is crucial to correctly plan and predict the
absorption coefficient of these components. Therefore, the design and material of the
aforementioned seating has to be planned properly.
Both types of seating are padded and clad in a fabric in order to absorbs sound and
dampen sound energy, which in turn diminishes echos.
4.3.5 Ceiling

Plaster & Plasterboard Ceiling
The ceiling is primarily plaster-coated and formed of plasterboards. Plaster has a hard
surface that has poor acoustic absorption qualities and therefore sound bounces off it
and back towards the ground. This ceiling has been designed in such a way as to
properly deflect the sound in the right direction towards the audience, and avoid
surfaces parallel to avoid flutter echoes.
27

This false plaster ceiling also functions to conceal ventilation system and the the fly
system inside which is comprised mainly of lighting rigs.
4.3.6 Stage
1. Timber Parquet Flooring
Wood floors are utilised for stage use as they are resilient and can withstand foot traffic,
as well as produce a longer reverberation time due to it being a hard, acoustically
reflective surface. Reverberation can be the cause of various issues if not appropriately
suited to the space or use, however in this case it is justified as it causes sound from
the stage sound more full.
The stage apron is constructed of a different, but similar-functioning material, which is a
laminated MDF-flooring. It has similar acoustic qualities, but costs less than solid timber.
2. Carpet Apron Absorber
Similar to the auditorium flooring, the apron is clad with a carpeting finish. However, the
underlayment is not required as prevention of floor vibrations is not required. The apron
absorber absorbs sound reflected from the auditorium that has bounced back towards
the stage.
28

4.4 Sound & Noise Sources
The auditorium is designed to produce and contain sound within its enclosed space via
the Audio Visual (“AV”) system installed. The control deck for the AV system is located
at the centre of the upper seating area for optimal sound monitoring. The sound
produced in the auditorium is contained via sound absorbing walls, seats, carpets, and
doors that minimizes sound leakages to the outside, whilst also keeping external noises
at a minimum.
The term “Sound” and “Noise” may be confused and can be subjectively defined based
on the effects it has on a particular person. Noise is generally defined as sound that is
unpleasant to the listener. Sound and Noise are both “decibel-independent”; a low db
noise is still considered as noise whereas a high db sound is still considered sound.
Both external and internal noises need to be considered when attempting noise
suppression in the design of an auditorium. External noise is defined as noise that
originates from outside the auditorium, and internal noise is defined as noise produced
from within the auditorium, most commonly from instruments, materials, and electrical
appliances.
29

4.4.1 Sound Sources
Internal sounds are amplified via the auditorium’s built in AV system, comprising of the
input and output components. The input components include dynamic utility
microphones, condenser microphones, electric pickups for guitars and bass and direct
input from electric musical instruments like keyboards. Output components include
amplifiers, array speakers (ceiling mounted) and stage monitors.
Dynamic Microphone Condenser Microphone Electromagnetic Guitar Pickup
Type, Location, and Number of Speakers
Speakers are used to amplify the sounds created on stage to the audiences and
are monitored and controlled by a sound engineer in the sound booth. The
speakers are mounted in an angled array from the ceiling at a height of
approximately 7 meters from the ground.
30

Speaker Arrays
There are 3 speaker arrays suspended from the ceiling directly in front of the
stage directed to the centre, left and right sides of the hall to ensure a balanced
transmission of sound to the entire hall. The speakers are configured in a 9 – 8 –
9 configuration whereby there are 9 speakers for each left and right arrays and 8
speakers in the centre array.
The speakers are installed in such a manner to avoid reflection from the flat floor
which can produce inconsistent amplification should the speakers be on ground
level.
Arrangement of Suspended Array Speakers
31

Subwoofers
Alternating between the 3 arrayed speakers are subwoofers that boosts the lower
frequency range of the sound, typically below 100 Hz. There is a total of 4
subwoofers which are also suspended from the ceiling of the stage. Instead of
being configured in an array similar to the speakers, the 4 subwoofers are
installed as single units as lower frequencies have slower attenuation and can
easily reach the audiences.
However, the output source of the subwoofers is pointed towards the concrete
wall behind it to produce indirect sounds which will be reflected to the audiences
via the angled ceiling. This method further reduces the attenuation of lower
frequency sounds.
Subwoofer Placement and Configuration
32

Monitors
Monitor speakers function to provide feedback to the performers on stage which
are situated in the blind spot area of the speakers.
It is placed on the stage floor facing the performers to ensure that they can hear
the sound they produce to help with synchronisation between different
instruments during performance.
Location of Floor Monitors
33

4.4.2 External Noises
Most of the external noise comes from the hallway areas surrounding the hall including
from the entrance foyer and the cafeteria on the right side of the auditorium, at
approximately ~50dB. However, the external noise from the cafeteria is reduced to an
approximated ~30dB when the door is completely shut.
34

There is also a back door behind the stage area which opens up directly to the outside
of DUMC. Since the door is not configured with a sound lock, external noise from the
parking and construction around the area can be heard quite significantly from the stage
at around ~60dB.
The level of noise is also dependent on the event taking place in the auditorium. During
Sunday services for example, when some of the doors are left partially opened and
more congregants are around in the hallway, there is significant increase in external
noise as compared to other days.
35

4.4.3 Internal Noises
Internal noise in the auditorium are mostly created by the sounds of electrical equipment
such as the AV deck, server, air conditioning, and minor static noise from fluorescent
lighting. These noises are constantly present when the hall is in use, but are often
dwarfed by the sound of events taking place on stage.
Noise is also created by the materials used in the auditorium when activities are
conducted, such as walking on the timber flooring on stage, the opening and closing of
the doors, the spring-loaded folding seats, as well as the opening and closing of the
sliding doors at the children’s section.
36

Air Conditioning
The biggest issue with conditioning the air for a space as large as the DUMC
Auditorium is that it produces a high amount of noise when high velocity blowers
supply air into the space, usually coupled with jet diffusers. However, the use of
these type of blowers are necessary as the diffusers are placed only around the
perimeter of the upper tier due to the high ceiling. Hence, a powerful stream of
cool air needs to be pumped into the centre from this perimeter array of jet
diffusers, producing noticeable noise.
Different types of diffusers are used in the auditorium depending on the
functionality, either return or supply of air.
Return
For return / intake air, single deflection return diffusers are used in
different sizes depending on its location. For first floor return air diffusers,
a larger version is used to return air placed at the ceiling.
Return Air Diffuser
37

Supply
For the supply of air, two types of diffusers are implemented in the design,
namely louver blade diffusers and the rounded jet diffusers. The normal
louver blades diffusers are installed where the ceiling is lower such as the
area below the upper tier. The blades deflect in all four directions to
spread the supply of air evenly. This type of diffuser still produces
noticeable noise, but at a much lower level relative to the jet diffusers.
Louvered Blade Diffuser Jet Diffuser
Jet diffusers are used to supply air to the center of the auditorium where
normal louvered diffusers would be inadequate due to the high ceiling.
They are placed at the perimeter of the upper tier pointed towards the
center of the auditorium and produces loud noise during operation. Based
on observation during the visit, the noise produced by only half of these
diffusers on was approximately ~55 dB.
38

Lighting Layout, Types of Lighting Fixtures, Functions
Most of the lighting fixtures in the auditorium are recessed lighting using
fluorescent energy saving light bulbs that are embedded in the high ceiling of the
center atrium. There are also strips of fluorescent tubes installed as up lights that
are suspended used to light up the ceiling of the upper tier seating area.
39

The main issue with fluorescent bulbs is the buzzing noise it produces which can
average at around ~35 dB. However, the noise produced from the lighting fixtures
are often dwarfed by the noise of the air conditioning system.
On top of the lighting for the audience seating areas, there are also stage lighting
which include spotlights installed at specific locations depending on its functions.
Sound Locks
The hall does not implement a sound lock at the entry/exit points. Hence,
external noise may penetrate from time to time depending on the intensity of the
noise. However, the hall uses heavy curtains on the doors to suppress external
noise, which may be adequate for a multi-purpose hall. The curtains also act as
sound absorbers to prevent sounds from the inside of the hall to leak to the
exterior hallways.
40

4.5 Sound Propagations and Related Phenomena
4.5.1 Sound Reflection
Reflection is often used in room acoustics to efficiently distribute and reinforce the
sound waves heard by the audience. More often than not, only 10% of what is heard in
a room is from direct sound; the other 90% is aided by reflective surfaces to redirect
more sound waves to the audience.
Audience members receive sound from both direct sound and reflected sound waves
These reflections should be kept under control so as not to bombard audience members
with too much noise to the point of discomfort or to create echoes.
This can be done by easily covering the right surfaces with sound-absorbing material.
Smooth surfaces reflect sound waves coherently, whereas rough surfaces would reflect
the waves in many different directions.
The ceiling of the auditorium is staggered in such a fashion that imitates the reflective
effects of a concave surface. Concave surfaces can cover a wider area of sound wave
41

distribution so that the sound waves get reflected to both the lower and upper levels as
well as farther-seated audience members.
Audience members seated more than 15m away from the performer or speaker should
require the aid of reflected sound waves of the sound source.
4.5.2 Echoes and Sound Delay
Echoes occur when the audience hears the reflected sound from a source with a
notable delay time after hearing the direct sound.
By using the formula of [ R1 + R2 - D = delay distance ] we can find out the delay time of
sound waves at a certain point in the auditorium by later substituting values in the
formula [ t = s/v ] specifically meaning [ delay time = delay distance / speed of sound ]
R1 = Incident distance
R2 = Reflection distance
D = Direct distance
TD = Delay time
VS = Speed of sound
Thus,
Delay time, [ TD = ( R1 + R2 - D ) / VS ] measured in milliseconds (ms).
42

[ ( R1 + R2 - D ) / VS = TD ]
1. (25.2 + 4.0 - 27.4) / 344 = 5.2ms
2. (22.6 + 5.6 - 25.0) / 344 = 9.3ms
3. (17.6 + 9.4 - 22.6) / 344 = 12.8ms
4. (13.4 + 12.0 - 19.0) / 344 = 18.6ms
5. (9.6 + 19.6 - 18.6) / 344 = 32.8ms
6. (8.6 + 14.8 - 11.6) / 344 = 40.1ms
For speech, the longest acceptable delay time is 40ms (14m); for music, the longest
acceptable delay time is 100ms (34m). The auditorium, for the most part, falls within the
acceptable range for delay time for both speech and music purposes.
43

4.5.3 Reverberation
Reverberation affects acoustic qualities of a certain space to give it a ‘dry’ or ‘wet’
sound, a by-product of, respectively, short and long reverberation times (seconds).
Desirable reverberation times in a given space are engineered purposefully, where as
shown below, help accentuate sound qualities:
Retrieved from:
http://www.industrial-electronics.com/measurement-testing-com/architectual-acoustics-2-SOUND-ABSORPTI
ON-2.html
44

4.5.3.1 Effective Surface Area
What proceeds is finding the reverberation time of DUMC on 3 octaves of 125Hz,
500Hz and 2000Hz to analyse the range and extent of reverb in the hall. The findings
can then tell us if the acoustics correspond with the multi-purpose usage
EFFECTIVE
SURFACE
AREA
MATERIALS SOUND ABSORPTION COEFFICIENT
125 Hz 500 Hz 2000 Hz
378.8 Concrete wall 0.01 0.01 0.02
1057 Carpet 0.03 0.05 0.35
192.7 Curtain 0.05 0.40 0.60
206.9 Timber parquet 0.40 0.20 0.15
950.7
116.7
144
1. Drywall
2. Timber
3. Foam
0.31
0.18
0.9
0.14
0.42
0.54
0.10
0.83
0.88
171
213
1. Padded chairs
2. Auditorium seats
0.08
0.13
0.15
0.59
0.18
0.61
32.4
15.4
1. Timber double door
2. Timber core door
0.14
0.30
0.06
0.15
0.10
0.10
1193
930
1. Plaster
2. Gypsum Plaster
0.30
0.45
0.10
0.80
0.04
0.65
24.7 Glass window 0.30 0.10 0.05
Σ (m2
x coefficient) 1415.05 1456.31 1661.77
45

4.5.3.1 RT60 of DUMC
This shows the measurement of how long it would take a sound to decay 60dB, suitable
for use in large halls, within context of DUMC.
RT60 OF DUMC (s)
125Hz 500Hz 2000Hz
2.1 2.0 1.8
Given the volume
46

4.5.4 Acoustical Defects and Design Issues
DUMC advertises itself as a multi-purpose hall, falling on the higher end of the optimum
RT measure across the frequency band, making it better suited for music. Unassisted
and unamplified speech suffers greatly, factoring in the distance needed for sound to
travel from centre stage to the 1st floor remote seats
4.5.4.1 Design Factor
Big halls are a problem in factoring in design strategies to for multi-purposes. The
DUMC stretches wider than 140° resulting in undesirable seating spots. In the case of
unassisted sound, at the average volume of a grown adult speech (85Hz - 150Hz), the
ambient sound intensity of the hall (45Hz) lowers intelligibility. Below is a table of sound
intensity level analysis at different ranges, across three octaves as well.
Distance (m) Sound Intensity Level (dB)
125Hz 500Hz 2000Hz
1 60.8 74.7 86.2
5 54.7 69.2 79.5
10 47.0 62.5 72.7
15 45.5 55.0 67.4
20 46.0 54.2 66.6
25 45.2 50.5 64.6
Note that the mean of the values correspond to the inverse-distance law that states that
for every doubling of distance from the incident sound, 6.02 dB is loss in one direction.
This simple experiment is conducted with a tone a generator with the specific
frequencies and at constant volume, although the air-conditioning (ambient) proved a
challenge to ensure controlled variables.
47

4.5.4.2 Flutter Echoes
The monitor room on the first floor might prove unpleasant to the surrounding seatings,
a result of flutter echoes that are reflected off of the parallel unpadded concrete walls
that contain the room. An overhead flat ceiling that sits (less than 17m) above the
monitor room is less susceptible to flutter echo but may still cause unwanted reflected
sound out and upwards.
4.5.4.3 Sound Shadows
The last four rows of the ground floor fixed seats will experience a dead sound
experience, caused by the surrounding absorbent materials and the extended corridor
overhead that blocks out reflected sound off the ceiling.
The phenomenon is known as sound shadows. These instance can be detected in a
few spaces of the hall, some for a the better, and some for the worse
4.5.4.4 Sound Transmission Anomalies
The pillars that support the extended corridor above can be designed and placed in a
more strategic manner, avoiding the risk of sound shadows and unwanted diffraction to
the row fixed seating arranged behind the 6 pillars.
48

4.5.5 DUMC as a Mixed-Use Auditorium
DUMC works well as a multipurpose hall as a whole, where weekly services comprise of
musical hymns and sermons, with an engineered reverberation time that falls well within
the range of a 100,000m3 hall. The ground floor is elevated toward the back to position
the fixed seats within sight lines while the ceiling panels serve as sufficient reflectors to
redirect sound toward the raked seatings on the upper floor, also well within sight lines.
This enables incident and reflected sound to be received by the ears across the hall.
The need to accommodate both the desirable qualities of music and speech leaves
room for criticism as well.
Assisted sound is managed through the utilisation of multiple speakers, increasing SIL
to better project sound across distances from centre stage, relying less on the careful
consideration of sound redirection. Unassisted speeches are muffled when seating on
the last four rows of the hall, almost blending into the ambient sound at 43dB.
The bottom row under the extended terrace are affected by loud air-conditioning at
45dB and is noticeable during speeches. In addition to that, the last four rows fall under
sound shadows from the terrace above, where aural experience tends to feel ‘dead’,
being contained in a sound-absorbent surrounding. In accommodating the need for
ample seating and amplified music, this is where the experience falls flat.
49

5.0 Observation, Discussions and Conclusion
Through the observations and measurements taken, we can conclude that as a
multipurpose hall that primarily focuses on speeches and music, the acoustic design of
the auditorium is optimized for such activities.
By prioritizing mid to high frequency sounds while muffling low frequency sounds, the
DUMC auditorium is able to reduce vibrations that would otherwise be transferred
throughout the church itself, which may disturb other activities that are going on in other
rooms. While unassisted speech doesn’t perform well in this auditorium it is not much of
a problem as speeches are expected to be conducted with the aid of speakers at all
times.
This project has allowed us to understand the acoustic design response based on the
typology and function of the DUMC auditorium and how specific adjustments are
needed to cater to the programmatic demands of an auditorium in general. The analysis
has made clear the relationship between acoustics and the materials, spatial planning
and context of an auditorium. The understanding of these relationships and concepts
would greatly benefit us in future design projects especially when acoustics are taken
into consideration.
The group would like to extend its utmost appreciation to Mr. Azim and Mr. Edwin who
have actively assisted throughout the group’s journey in completing this project.
50

6.0 References
● http://www.sxsevents.co.uk/about/resource-hub/explanatory-articles/sound-delay
-explained
● http://www.theatresolutions.net/auditorium-seating-layout/#theater-forms
● http://www.industrial-electronics.com/measurement-testing-com/architectual-aco
ustics-2-SOUND-ABSORPTION-2.html
51

Building Science II Project 1 - Acoustic Design

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