Building Science 2 - Project 1 - MBPJ Civic Hall : A Case Study on Acoustic Design

BUILDING SCIENCE II (BLD 61303) School of Architecture, Building and Design Bachelor of Science (Hons) Architecture

PROJECT 1 - MBPJ CIVIC HALL A CASE STUDY ON ACOUSTIC DESIGN

Tutor : Mr.Azim Sulaiman Eisyah Faridah Binti Ahmad Nazari Viktor Zeidler Lim

0328624 1006aH79876

CONTENTS 1. Introduction 1.1 General Information 1.2 Context and Location 1.3 Methodology 1.3.1 Data Collection Method 1.3.2 Measuring and Recording 1.4 Auditorium Design 1.4.1 Architectural Drawings 1.4.2 Form and Layout of Auditorium 1.4.3 Levelling and Arrangement of Seats

2. Acoustical Treatment and Components 2.1. Materials 2.1.1 Material of the walls 2.1.2 Material of the floor 2.1.3 Material of the ceiling 2.1.4 Other materials 2.2 Total Absorption of Surfaces

3. Acoustical Analysis 3.1 Sound Sources 3.1.1 Sound Reinforcement 3.1.2 System Components 3.2 Sound Propagation 3.2.1 Sound Level Measurement 3.2.2 Sound Reflection and Diffusion 3.2.3 Sound Absorption 3.3 Sound Defect 3.3.1 Sound Delay and Echo 3.3.2 Sound Shadow Area 3.4 Noise Intrusion 3.4.1 External Noise 3.4.2 Internal Noise

4. Reverberation Time 4.1 Introduction 4.2 Reverberation Time Calculation

5. Conclusion 5.1 Acoustic Considerations & Suggestions

6. References BUILDING SCIENCE II | BLD61303 | PROJECT 1 - MBPJ CIVIC HALL : A CASE STUDY ON ACOUSTIC DESIGN

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1.

INTRODUCTION

BUILDING SCIENCE II | BLD61303 | PROJECT 1 - MBPJ CIVIC HALL : A CASE STUDY ON ACOUSTIC DESIGN

INSERT PHOTO

Fig 1.0 Front facade of MBPJ Civic Hall.

1.1 General Information The MBPJ Civic Hall is located on Jalan Yong Shook Lin in Petaling Jaya, Selangor. It houses an auditorium, a multipurpose banquet hall and a lecture room. It is used to cater to events like weddings, stage performances, school concerts and open house parties though it used to be a common location for IT fairs and exhibitions.

The hall is located on the grounds of the administrative building of the Majlis Bandaran Petaling Jaya (MBPJ) Named after the famous nearby cinema, the area is also known as PJ New Town or ‘PJ State.' The building is designed in a Brutalist Style introduced largely by British architects to Malaysia in the 50s and inspired by the early works of Le Corbusier consisting mainly of large monolithic concrete forms with prominent geometric shapes.

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Fig 1.1 Location of MBPJ Civic Hall on Google Maps.

1.2 Context and Location The Civic Hall itself is within the same premises as the Petaling Jaya City Council, albeit it being on elevated land. It is accessible via the shared parking lot between the two buildings or a separate vehicular entrance that leads to the hall’s drop off area and lobby. There is also an access route that leads to the back of the hall for any service vehicles that need to load or unload items.

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1.3 Methodology 1.3.1 Data Collection Method The acoustic quality of the auditorium is investigated through the observation, measurement and calculation of the sound levels from a single, constant sound source at various locations within the auditorium. The readings are used to analyse the acoustical phenomena in the auditorium, also taking into account the effect of noise intrusion. Several information are to be collected for the analysis including : 1.

Technical drawings and dimensions of the auditorium that is crucial in obtaining the surface areas and volume of the auditorium for the calculation of reverberation time.

2.

Location and types of materials used for the Auditorium with the evidence of photographs and diagrams to assist with the calculation of the total surface absorption.

3.

Location and types of sound system components used in the auditorium.

1.3.2 Measuring and Recording Equipment Smartphones were mainly used to capture photographs. A sound meter app was used for measuring the sound properties in the auditorium. It was used to measure the sound intensity levels at various locations in the auditorium to determine the concentration of the sound and also the background noise levels. It was also used as a sound source.

Fig 1.3 Smartphone

Fig 1.4 dB Meter Sound Measuring App

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Sound Level Meter Digital sound meter was used to measure the acoustics within the auditorium. The unit of measurements for the acoustics is in db which is short for decibels. It was used to measure the sound intensity levels at various locations in the auditorium to determine the concentration of the sound.

Fig 1.5 Digital Sound meter

Measuring Tools The laser measuring tool is effective and accurate in measuring the dimensions of the space and the various elements. It was also used to measure the distances of the positions of the sound meter readings taken from the sound source. The measuring tape is mostly used to measure shorter, reachable areas.

Fig 1.6 Laser Measuring Tool

Fig 1.7 Measuring Tape

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1.4 Auditorium Design 1.4.1 Architectural Drawings

Fig 1.8 Site plan

Fig 1.9 Plan of MBPJ Civic Hall

BUILDING SCIENCE II | BLD61303 | PROJECT 1 - MBPJ CIVIC HALL : A CASE STUDY ON ACOUSTIC DESIGN

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Fig 1.10 Auditorium Plan

Fig 1.11 Section of Auditorium

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1.4.2 Form and Layout of Auditorium The layout of the building is asymmetrically balanced with the auditorium located on the left from the main lobby opposite the Banquet Hall. The Auditorium is an end stage layout, whereby the audience is facing the stage from one side. It is designed in a ‘Shoebox’ shape with a slight tilt of no more than 5 degrees from the centerstage.

Fig 1.12 Shoebox Shape Plan of Auditorium

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1.4.3 Levelling and Arrangement of Seats The auditorium is an end stage layout where the audience are only facing from one side. There are 9 divides seating zones, 6 below and 3 above. There is a consistent row of sloping seats with the side seating zones slightly angled facing towards the centerstage. Back section of seats is at a steeper slope for visibility along with an elevated balcony of seats above, also known as a gallery.

Fig 1.13 View of Auditorium seats from backrow

Fig 1.14 View of Auditorium seats from centerstage

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2. ACOUSTICAL TREATMENTS AND COMPONENTS

BUILDING SCIENCE II | BLD61303 | PROJECT 1 - MBPJ CIVIC HALL : A CASE STUDY ON ACOUSTIC DESIGN

2.1 Materials 2.1.1 Material of the walls The walls consists of two timber batten cladding of two different types and exposed concrete structures covered in rough textured plaster. The timber battens that are recessed in the walls are arranged diagonally, and the rest vertically. The rough concrete is highly effective at diffusing sound as the sound waves are diffracted and dispersed at various angles.

rough plastered concrete smooth plastered concrete timber batten cladding

Fig 2.1 Section of Auditorium highlighting the various wall materials

Fig 2.2 Side Wall concrete structure and timber cladding (left) with a close-up of the materials (right)

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Vertical Timber Diagonal Timber

Fig 2.3 Section of Auditorium highlighting the two types of timber cladding

Timber Battens are arranged both vertically and diagonally. Vertical battens are about 100mm wide spaced apart with a gap of about 5-10mm whereas diagonal battens are closely arranged with chamfered edges, recessed into the wall, diffusing the sound by dispersing them at multiple angles.

Vertical timber battens are supported by horizontal members backed with a fabric membrane. The cavity between the battens help dampen the sound due the entrapment of sound waves which are also absorbed by the fabric membrane.

inc

dispersed

ide

nt

absorbed Fig 2.4 Plan detail of Vertical Timber Batten Wall Illustrating the behavior of sound waves

Vertical Timber Cladding

DIagonal Timber Cladding

Absorption Coefficient (500Hz) : 0.15

Absorption Coefficient (500Hz) : 0.10

Total Area : Side Walls + Back Wall : (212m² x 2) + 315m² = 739m²:

Total Area : Left Wall + Right Wall : 78m²: + 78m²: = 156m²:

Total Surface Absorption : 0.15 x 739 = 110.9 sabins

Total Surface Absorption : 0.10 x 156 = 15.6 sabins

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Rough Concrete Smooth Concrete

Fig 2.5 Section of Auditorium highlighting the two types of concrete surfaces

The rough concrete surface is most prominent on the sidewalls facing the center of the auditorium whereas the smooth concrete surface is mainly around the stage area. The rough concrete has a higher sound absorption coefficient compared to smooth concrete due to its uneven textured surface that is highly effective at diffusing sound. The sound waves are diffracted and dispersed at various angles, eliminating the direct reflection of sound and suppressing the effect of echoes.

specular reflection

scattered diffusion

Fig 2.6 Diagram illustrating the behaviour of sound waves when in contact with a smooth surface (left) and rough surface (right)

Smooth Surfaced Concrete

Rough Surfaced Concrete

Absorption Coefficient (500Hz) : 0.02

Absorption Coefficient (500Hz) : 0.06

Total Area : Stage Walls + Front Stage + Balcony + Back Walls : (108m² x 2) +35m² +110m² + 240m² = 601m²:

Total Area : Side Walls : (150m² x 2): = 300m²:

Total Surface Absorption : 0.02 x 601 = 12.02 sabins

Total Surface Absorption : 0.06 x 300 = 18 sabins

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2.1.2 Material of the Floors Wool carpet flooring is applied over the entire Auditorium except for the Stage, which has solid timber flooring. The application of wool carpet flooring helps to reduce noise by absorbing both air-borne and structure-borne sound such as floor-impact noise from footsteps.

Fig 2.7 Ground Floor Plan (left) and Balcony (right) of Auditorium highlighting the two types of flooring

timber flooring

carpet flooring

Solid Timber

Medium Pile Carpet

Absorption Coefficient (500Hz) : 0.15

Absorption Coefficient (500Hz) : 0.30

Total Area : Front Stage : 235m²

Total Area : Ground Floor + Balcony : 660m²: + 238m²: = 898m²:

Total Surface Absorption : 0.15 x 235 = 35.25 sabins

Total Surface Absorption : 0.30 x 898 = 269.4 sabins

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2.1.3 Material of the Ceiling The Auditorium is mainly covered by a rough plaster ceiling with a series of curved arch-like beams extending from the sidewalls across the Auditorium.

It’s curved-in, concave feature causes sound to reflect into concentrated areas directly below the arches.

The plaster ceiling below the balcony is partially staggered sloping down to the front when it curves upwards to form the front face of the balcony wall.

Fig 2.8 Section of Auditorium highlighting ceiling location

concentrated area Fig 2.9 Sectional Diagram of Auditorium ceiling indicating concentrated reflection of sound

Ceiling Absorption Coefficient : 0.06 Total Ceiling Area : Auditorium main ceiling +Ceiling below Balcony : 860m² + 310m² = 1170m²

Fig 3.3 Auditorium main ceiling with arch-like structure spanning across

Total Surface Absorption : 0.06 x 1170 = 70.2 sabins

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2.1.4 Other materials Drapery Seatings

Fig 2.10 Row of Auditorium seats

Other materials in the auditorium are additional factors that help improve the quality of sound absorption in the space. The auditorium consists of 977 tip-up seats, each upholstered with a soft padding made out of a porous fabric material. Other than that, the drapery used to cover the 5 exits to toilets and staircases also improves sound absorption with its use of medium velour cloth and pleated nature.

Fig 2.11 (Left to right) Drapery on one of the exits, row of seats, singular seat and zoom in on upholstered fabric seat’s texture BUILDING SCIENCE II | BLD61303 | PROJECT 1 - MBPJ CIVIC HALL : A CASE STUDY ON ACOUSTIC DESIGN

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2.2 Total Absorption of Surfaces Material

Vertical Timber

Location

Area (m2)

Absorption Coefficient

Left Wall

212m²

0.15

Right Wall

212m²

0.15

Back Wall

315m²

0.15

Left Wall

78m²

0.1

Surface Absorption (m2 sabins)

110.9

15.6

Diagonal Timber

Smooth Concrete Wall

Right Wall

78m²

0.1

Balcony Front Wall

110m²

0.02

Back Wall

240m²

0.02

Stage Left Wall

108m²

0.02

Stage Right Wall

108m²

0.02

Stage Front Wall

35m²

0.02

Left

150m²

0.06

Right

150m²

0.06

Stage

235m²

0.15

Ground Floor

660m²

0.30

18

Rough Concrete Wall

Solid Timber

12.02

35.25

269.4

Medium Pile Carpet Balcony

238m²

0.30

Entire Auditorium

860m²

0.06

70.2

Rough Plaster Balcony

310m²

0.06

Medium Velour Drapery

Exits

88m²

0.49

43.12

Fabric upholstered

Tip-up Seats

977 Nos.

0.8 per seat

781.6

Total Surface Absorption (m2 sabins)

1356.09

Fig 2.12 Table of Total Absorption of Surfaces calculations

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3. ACOUSTICAL ANALYSIS

BUILDING SCIENCE II | BLD61303 | PROJECT 1 - MBPJ CIVIC HALL : A CASE STUDY ON ACOUSTIC DESIGN

3.1 Sound Sources 3.1.1 Sound Reinforcement A sound reinforcement system compromising of a series of components is used to accommodate the large volume of the auditorium in order to enhance and distribute live or pre recorded sound over a wider area, targeting distant or ‘sound-shaded’ areas that receive less sound while retaining or enhancing the quality of the existing audio, rather than just amplifying it.

Fig 3.0 Plan of Auditorium indicating the placement and coverage of the sound system components

Central Built-in Loudspeaker

2-Way Loudspeaker (JBL MRX525)

Subwoofers (JBL MRX518S)

Compact Subwoofers (JBL SB210)

Fig 3.1 Section of Auditorium illustrating the placement and coverage of the sound system components BUILDING SCIENCE II | BLD61303 | PROJECT 1 - MBPJ CIVIC HALL : A CASE STUDY ON ACOUSTIC DESIGN

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3.1 Sound Sources 3.1.2 Sound System Components

1 Central Built-in Loudspeaker

4 Subwoofers (JBL MRX518S)

The central loudspeaker is built-in at the top centre of the stage curved ceiling, angled facing towards the center of the auditorium. It consists of a grille made of thermoset composite coated steel covering a multi-layer foam.

Frequency Range: 42 Hz - 320 Hz Power Capacity: 800W Program Power; 400w continuous pink noise Grille: Thermoset composite coated steel, weathermax multi-layer foam

The MRX518S is a compact, high power subwoofer system containing a 18 inch woofer in a front-loaded, vented enclosure.

There are two pairs of subwoofers, one stacked on the other, at both front corners of the stage providing a wide and even distribution of sound to the sides of the auditorium.

Frequency Range: 40 Hz - 200 Hz Power Capacity: 500 W / 1000 W / 2000 W Sensitivity: 94 dB SPL; 100 dB SPL Nominal Impedance: 4 Ohms

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3.1 Sound Sources 3.1.2 Sound System Components

6 Dual 15" 2-Way Loudspeaker

2 Compact Subwoofers

(JBL MRX525)

(JBL SB210)

High performance two-way speaker with a single high power amplifier capable of reinforcing bass and playing high quality audio.

A compact subwoofer which provides high output, low frequency sound reinforcement. The Control SB2210 produces warm, punchy low-end sound with low distortion.

The position of the two way speaker system with 70° coverage angle of an audience allows splaying of multiple enclosures without excessive coverage overlap.

The subwoofers are fixed at the side walls of facing the central seating area at the Balcony to increase the distribution of sound.

Frequency Range: 40 Hz - 20kHz Sensitivity: 94 dB SPL; 100 dB SPL Nominal Impedance: 4 ohms Power Capacity: 800 W / 1600 W / 3200 W Dimensions (HxWxD): 1240mm x 535mm x 460mm

Frequency Range: 42 Hz - 200 Hz Sensitivity: 94 dB SPL; 98dB @ 1m Nominal Impedance: 4 Ohms Power Capacity: 400 W / 800 W / 1600 W Dimensions (HxWxD): 692 mm x 432 mm x 470 mm

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3.2 Sound Propagation 3.2.1 Sound Level Measurement In order to get an accurate study of the acoustical quality of the auditorium, there were two sets of sound level readings we had to take; 1) sound level measurements without a sound source ie.background 2) sound level measurements with a constant sound source emanating from the centre of the stage.

A

C

B

A - 32.5 dB B - 37.5 dB C - 55.0 dB

D - 37.5 dB E - 41.5 dB

D

E

Fig 3.2 Row of Sound level measurements without a sound source on Ground Floor (left) and on the Balcony Gallery (right)

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A - 59.1 dB B - 60.3 dB C - 58.9 dB D - 52.8 dB A

D

G

J

B

E

H

K

E - 52.2 dB F - 52.6 dB G - 51.3 dB

C

F

I

L

H - 52.8 dB I - 51.2 dB J - 48.5 dB K - 50.1 dB L - 48.3 dB

M - 53.5 dB M

P

N

Q

N - 54.1 dB O - 53.5 dB P - 51.8 dB

O

R

Q - 51.8 dB R - 51.8 dB

Fig 3.3 Row of Sound level measurements with a sound source at the centre of the stage on Ground Floor (left) and on the Balcony Gallery (right)

From the data it can be observed that the background sound levels are louder towards the back of the auditorium, where noise could potentially be the main factor. The sound level recordings taken with the constant sound source indicates a significant decrease in sound level at the ground floor back seats row J,K and L and is actually lower compared to the Balcony seats above.

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3.2 Sound Propagation 3.2.2 Sound Reflection and Diffusion Sound reflection, sound diffusion and sound absorption are three sound behaviours that should be taken into account when undertaking the acoustic conditioning of a space.

Sound reflection is the behaviour of sound waves reflecting off surfaces whereby the angle at which they approach the surface, known as incident wave, will equal to the angle they reflect off the surface. In a room filled with non-parallel surfaces, the standing waves are broken apart, which in turn will deliver more acoustic balance to the room in comparison to a room with parallel walls, which would end up having standing waves that are mirrored or repeated sound paths, resulting in unbalanced ‘focused’ or ‘dead’ spots; over-concentrated or inaudible areas.

A - 59.1 dB B - 60.3 dB C - 58.9 dB D - 52.8 dB A

D

G

J

INSERT DIAGRAM B

C

E

F

H

I

K

L

E - 52.1 dB F - 52.6 dB G - 51.3 dB H - 52.8 dB I - 51.2 dB J - 48.5 dB K - 50.1 dB L - 48.3 dB

Fig 3.4 Sound reflection path with the row of sound level measurements with a sound source at the centre of the stage on Ground Floor

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Sound diffusion is the scattering or dispersion of sound waves in different directions. It is crucial in architectural acoustics in order to produce a uniform distribution of sound, accentuating the natural qualities of music and speech while preventing the occurrence of undesirable acoustical defects. Sound diffusion may be achieve with the aid of surface irregularities, perforation and uneven or staggered elements. An alternate application would be the use of sound reflective and/or sound absorbing treatments.

Fig 3.5 Sectional diagram showing the reflected sound path on the ceiling (left) with a callout closeup of the sound diffusion on the surface (right)

60.3 dB

52.8 dB

54.1 dB

Fig 3.6 Sectional diagram showing the reflected sound path and the sound level measurements with a sound source at those particular spots

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3.2 Sound Propagation 3.2.3 Sound Absorption When a sound wave strikes one of the surfaces of a room, some of the sound energy is reflected back into the room and some penetrates the surface.

Parts of the sound wave energy are absorbed by conversion to heat energy in the material, while the rest is transmitted through. The level of energy converted to heat energy depends on the sound absorbing properties of the material.

Sound absorbing materials affects the reverberation time and the noise in level in the auditorium. It works through friction when sound has access to the fine pores and tiny holes that one finds in porous and fibrous absorbers.

Absorbers are most efficient in the higher frequency and middle to low if sufficiently thick or backed by a buffer of gap of airspace. The importance of the absorber comes in controlling the ambience or reverberant time to not exceed the room’s natural threshold, causing ear fatigue; whereby communication will then require much more attention.

Fig 3.7 Section Diagram illustrating the absorption of sound. http://www.technature.ca/acoustics-101/sound-absorption/

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3.3 Sound Defects 3.3.1 Sound Delay and Echo When sound strikes a surface it creates an echo. Convex surfaces lead to dispersed reflections whereas concave surfaces result in concentrated reflections. A time delay of 40msec for speech and 100msec for music perceived as a sound distinct from that travelling directly from source to listener is deemed as an echo. The formula to calculate time delay is as follows:

(R1 + R2 - D ) / 0.34 R1 + R2 is the total distance of sound reflection travelled from the source D is the direct distance of sound travelled from the source 0.34 is the speed of sound (meters per millisecond) We make measurements for various points of varying distances from the sound source to investigate time delayed reflection in the auditorium. To measure distances from section drawings, the points are taken along the central axis.

7.0m

8.2m

7.5m

Fig 3.8 Sound reflection and distances on ground floor front area

Calculation of Sound Delay in millisecond(msec) :

(R1 + R2 - D ) / 0.34 = (6.0m + 8.2m - 7.1m) / 0.34 = 22.6 msec

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11.9 m 10.5 m 14.6 m

Fig 3.9 Sound reflection and distances on ground floor central area

Calculation of Sound Delay in millisecond (msec)

(R1 + R2 - D ) / 0.34 = (10.5m + 11.9m - 14.6m) / 0.34 = 22.9 msec

11.5 m 8.1 m

16.3 m

Fig 3.10 Sound reflection and distances on Balcony gallery front area

Calculation of Sound Delay in millisecond (msec)

(R1 + R2 - D ) / 0.34 = (8.1m + 11.5m - 16.3m) / 0.34 = 9.7 msec

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3.3 Sound Defects 3.3.2 Sound Shadow A sound shadow is an area through which sound waves fail to propagate due to obstructions or disruption of the waves via phenomena such as wind currents, physical structures, or sound barriers.

The upper balcony gallery has higher sound levels due to the fact that the sound from the stage is reflected off of the ceiling into the upper level. The ceiling is designed with curved concave features, creating a concentration of sound waves to most areas above the auditorium balcony. The sound energy produced from the stage is not enough to propagate itself all the way to the back of the auditorium. The seating area below the upper balcony ends up in the sound shadow area due to the position of the upper balcony which blocks the reflected sound waves from reaching the area beneath it.

Fig 3.11 Diagram showing sound reflection within the auditorium

A

D

G

J

B

E

H

K

C

F

I

G - 51.3 dB

J - 48.5 dB

H - 52.8 dB

K - 50.1 dB

I - 51.2 dB

L - 48.3 dB

L

Fig 3.12 Plan indicating the sound level recordings in the sound shadow area BUILDING SCIENCE II | BLD61303 | PROJECT 1 - MBPJ CIVIC HALL : A CASE STUDY ON ACOUSTIC DESIGN

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3.4 Noise Intrusion Sound can be transmitted by air, called air-borne sound transmission. Sound waves travel the air produced through building openings; windows, doors, pipes, grills, etc. Sound can also travel through structures ie. structure-borne sound; whereby the close and compact solid atoms vibrate at a frequency that allows sound to be transmitted through any solid form at long distances.

This occurs through building elements such as floors, walls and ceilings.

3.4.1 External Noise

Fig 3.13 (Above) Aerial view of MBPJ Civic Hall highlighting main external noise sources and the trees surrounding the building

Fig 3.14 (Left) A google maps view that displays the location of MBPJ Civic Hall from the mainroad

The MBPJ Civic Hall is tucked away from the main road reducing the external noise intrusion from the mainroad traffic. This does not exclude the outdoor noises of the vehicles passing nearby and around the building. Nonetheless, the level of external noise from vehicles is insignificant and the landscaping and use of trees act as sound barriers that buffer the noise.

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3.4 Noise Intrusion 3.4.2 Internal Noise Within the building itself, there are numerous noise intrusions. Firstly, the entrance into the auditorium is not separate from the main lobby of the hall. It shares a space with the entrance to the banquet hall on the other end of the hall and the main reception area. The interior of the lobby is fixed with almost entirely marble slabs, which unfortunately help exacerbate any echoes from possible sounds made within that space. The doors at the main entrance into the auditorium is also poorly maintained, old, and doesn’t close properly, leaving gaps that allow sound to seep into the auditorium.

Fig 3.15 (Above) main entrance doors to the auditorium (Left) Entrance Lobby area facing the entrance to the Auditorium

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3.4 Noise Intrusion 3.4.2 Internal Noise

Audience toilet External Passage

Audience seating area

Backstage area

Audience toilet External Passage

Fig 3.16 Diagram of Occupancy Noise Intrusion

The occupants can also provide noise intrusion. Possible air-borne noise intrusion include sounds of chatter from the audience in the seating area, as they enter the auditorium and take their seats. Structure-borne noise intrusion can amplify the sound of doors slamming or footsteps backstage or along the corridors within the auditorium. A way to combat this would be to supply soft floor finishes like carpets to reduce the noise intrusion.

Fig 3.17 Audience chatter is one of the main noise intrusions in the auditorium

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3.4 Noise Intrusion 3.4.2 Internal Noise

Air Conditioning (from ceiling)

Backstage toilet

Audience toilet

Air Lobby conditioning (From below balcony)

Fig 3.18 Section indicating noise intrusion from building systems

The building’s mechanical and electrical services can also create noise intrusion through structure-borne transmission. There are air-conditioning ducts from the ceiling and below the balcony that make noise, and the ones that are not maintained make even more noise. The toilets for both the audience and backstage access also create noise intrusions from the sound of flushing, water flowing through the pipes, pipings, etc. In order to minimise the noise intrusion from these aspects, the building managers would have to ensure that all are maintained well and are up to that. Furthermore, additional soundproofing on the parts of the auditorium that have noisy mechanical services could lessen the noise intrusion as well.

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4. REVERBERATION TIME

BUILDING SCIENCE II | BLD61303 | PROJECT 1 - MBPJ CIVIC HALL : A CASE STUDY ON ACOUSTIC DESIGN

4.1 Introduction Reverberation time (RT) is the time required for the sound in a room to decay over a specific dynamic range, usually taken to be 60 dB, when a source is suddenly interrupted. The Sabine formula relates the RT to the properties of the room.

Reverberation time is essential in determining the quality of music and the audibility of speech in a given space. When room surfaces are highly reflective, sound continues to reverberate as the waves that cause reverberation loses energy as they are absorbed at each successive reflection. The effect of this condition is described as a live space with a long reverberation time. A high reverberation time will cause a buildup of noise level in a space.

The formula for calculating reverberation time :

RT = 0.16V A

Uses

RT=Reverberation time(seconds) V=Volume(m3) A=Total absorption of room surfaces (m2 sabins)

Small Rooms (750m³)

Medium Room (750-7500m³)

Large Rooms (>7500m³)

Speech

0.75s

1.00s

1.50s

Multi-purpose

0.75 - 1.00s

1.00 - 1.25s

1.50 - 2.00s

Music

1.00s

1.00 - 2.00s

2.00 or mores

BUILDING SCIENCE II | BLD61303 | PROJECT 1 - MBPJ CIVIC HALL : A CASE STUDY ON ACOUSTIC DESIGN

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4.2 Reverberation Time Calculation

Fig 4.1 3D DIagram of MBPJ Civic Hall illustrating the volume extrusion from the side wall

Volume = Total Area of Side Wall X Width of Auditorium = 548m² X 25m = 13700m3

A = Total Absorption of All Surfaces = 1356.09 m2 sabins

RT = 0.16V A

RT=Reverberation time(seconds) V=Volume(m3) A=Total absorption of room surfaces (m2 sabins)

RT = 0.16 (13700) 1356.09 = 1.62 seconds BUILDING SCIENCE II | BLD61303 | PROJECT 1 - MBPJ CIVIC HALL : A CASE STUDY ON ACOUSTIC DESIGN

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5. CONCLUSION

BUILDING SCIENCE II | BLD61303 | PROJECT 1 - MBPJ CIVIC HALL : A CASE STUDY ON ACOUSTIC DESIGN

Fig 5.1 General purpose Auditorium ideal reverberation time chart http://230nsc1.phy-astr.gsu.edu/hbase/Acoustic/revtim.html

From the reverberation time calculated of the MBPJ Civic Hall auditorium, it is considered a large room at 13700m3 (>7500m3) and classifies as a multipurpose auditorium for general use and is suitable for speeches and seminars but it is not suitable for hosting high quality live musical and choir performances due to its dry acoustics and relatively short reverberation time of 1.62 seconds.

A possible solution to achieving a higher reverberation time to accommodate musical performances would be to reduce the amount of sound absorbing components by for example removing the amount of carpeted flooring and drapery within the auditorium seating area or to temporarily covering parts of the absorbing surface, for example the timber cladding; with a more reflective material such as smooth plasterboards with lower absorption coefficients.

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5.1 Acoustic Considerations & Suggestions 1.

There should be adequate loudness in every part of the auditorium, particularly the remote seats.

2.

Sound energy should be uniformly distributed (diffused) in the room.

3.

Optimum reverberation characteristics should be provided to allow the most favourable reception of the program material by the listeners.

4.

Noises and vibrations which would interfere with listening or performing should be excluded or reasonably reduced in every part of the room.

5.

The room should be free of acoustical defects such as echoes, long delayed reflections, flutter echoes, sound concentration, sound shadow and room resonance.

The rough texture although slightly more absorbing compared to the smooth concrete does not act as an effective acoustic feature in distributing an even or balanced sound in comparison to the timber cladding. Upkeep and maintenance of the condition of the doors at main entrance should also be implemented to prevent noise intrusion from the lobby outside.

Concave ceiling also causes ‘concentrated’ or ‘focused’ spots in the upper balcony gallery area causing acoustic imbalance. However, the sound reinforcement system can be effectively utilised to cover ‘dead spots’ and improve the distribution of sound.

Balcony gallery creates sound shaded area beneath that receives less sound and could be improved through the incorporation of reflective panels on the side walls near the opening at the center to direct more sound to the back area. To prevent any sound defect particularly echoes from occurring, acoustic panels of absorbing nature such as perforated timber of medium high absorption coefficient would assist in diffusing sound, reducing the amount of reflected sound and subsequently eliminating echoes, creating a clearer and more pleasant acoustical experience. Sound reinforcement can also be installed to improve the distribution of the sound within the sound shaded area.

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6. REFERENCES

BUILDING SCIENCE II | BLD61303 | PROJECT 1 - MBPJ CIVIC HALL : A CASE STUDY ON ACOUSTIC DESIGN

Books McMullan, R. (2012). Environmental science in buildings, 7th Edition. Basingstoke: McMillan.

Egan, M. D. (2007). Architectural Acoustics. J. Ross Publishing.

Cavanaugh, W. (2009). Architectural Acoustics: Principles and Practice, 2nd Edition. John Wiley & Sons.

Hardy, H. (2006). Building type basics for performing arts facilities. Hoboken, N.J.: John wiley & Sons.

Szokolay, S.V. (2004). Introduction to architectural science: the basis of sustainable design. Oxford: Architectural Press.

Websites Industrial Electronics. (2010). Room Acoustics. Retrieved April 18, 2021, from http://www.industrial-electronics.com/measurement-testing-com/architectual-acoustics-3-0.html TechNature. (n.d.). Acoustics 101. Retrieved April 18, 2021, from http://www.technature.ca/acoustics-101/ AcousticsFREQ. (2019). Sound-Absorbing Drapery: Theory & Application. Retrieved April 21, 2021, from http://acousticsfreq.com/sound-control-acoustic-curtain/ JCW Acoustic Supplies (n.d.) Absorption coefficients of common building materials and finishes.

Retrieved April 21, 2021, from https://www.acoustic-supplies.com/absorption-coefficient-chart/ HyperPhysics (n.d.). Auditorium Acoustics. Retrieved April 25, 2021, from https://hyperphysics.phy-astr.gsu.edu/hbase/Acoustic/auditcon.html Acoustic.ua. (n.d.). Absorption Coefficient Data List. Retrieved April 25, 2021, from http://www.acoustic.ua/st/web_absorption_data_eng.pdf ArchDaily. (2019). Understanding Sound Absorption and Diffusion in Architectural Projects. Retrieved May 7 , 2021, from https://www.archdaily.com/912806/understanding-sound-absorption-and-diffusion-in-architecturalprojects

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