Download Noise Control through Architectural Design

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CONTENTS
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Lesson 1
– Noise Control in Architecture
• What is noise?
• Sound transmission in architecture
• Noise Control through architectural design
| Noise Control in Architecture | Lesson 1 – Noise Control in Architecture
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Lesson 1
Noise Control in Architecture
| Noise Control in Architecture | Lesson 1 - What is Noise?
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What is Noise?
In daily life, noise means unwanted
sound.
As you have no doubt experienced,
unwanted sounds can include
distractions, sounds that are loud
enough to damage hearing and
even sound leakage that could
affect privacy.
In architecture, one of the many goals of the designer is to create rooms and buildings
that maximize sound performance. This means that unwanted sounds should be
prevented, and desired sounds should be enhanced.
| Noise Control in Architecture | Lesson 1 - What is Noise?
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What is Noise?
Sound Intensity I and Sound Intensity Level L
Sound intensity is a scientific concept distinct from the more subjective “loudness”.
It is defined as power of sound wave per unit area (Wm-2).
For example, sound intensity from ticking of watch is around 1 x 10-11 Wm-2, but a
jet taken off generates 1 x 102 Wm-2. Difference of powers of sound wave between
the watch ticking and a jet is 1013 times.
This scale is not comprehensive enough to tell the loudness of sound. A logarithmic
scale is used to measure sound intensity. It is called sound intensity level. Sound
Intensity Level is defended as:
L = Sound intensity level (dB);
I = Measured sound intensity (Wm-2); and
I0 = Standard sound intensity (Wm-2), the softest
sound intensity that human ear can hear.
The standard reference of I0 is 10-12 Wm-2.
| Noise Control in Architecture | Lesson 1 - What is Noise?
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What is Noise?
Difference Between Noise and Sound Intensity Level
Noise is a subjective and relative perception, but sound intensity level is a
scientific measure of the power of sound.
Even if a sound source has a relatively low sound intensity level, some individuals
might find a certain frequency of sound wave annoying because the human ear
reacts differently to different frequencies of sound (pitches) and the hearing ability of
individuals is subjective.
Sound intensity level can only be used as a standard to identify the volume of
sound that could cause hearing damage. It does not represent the exact
perception of the sound to individuals.
| Noise Control in Architecture | Lesson 1 - What is Noise?
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What is Noise?
Sound Transmission in Architecture
Sources of Noise
The two major sources of noise in architecture are:
1.Airborne noise, or sound waves transmitted from a source to a receiver through the air.
2.Structure-borne noise is caused by vibration from within the building caused by footsteps or
machines. The vibration is directly transferred through the building’s structures and materials.
A
B
C
A. The sound of a plane’s engine is a kind of exterior airborne sound that may affect communities
near airports.
B. The MTR’s operating systems are quiet, but the vibration of the train rail generates exterior
structure-borne noise.
C. In a gymnasium, cheering spectators may cause interior airborne noise to the surrounding rooms,
while the athletes’ activities generate interior structure-borne noise.
| Noise Control in Architecture | Lesson 1 - Sound transmission in architecture
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What is Noise?
Sound Transmission in Architecture
| Noise Control in Architecture | Lesson 1 - Sound transmission in architecture
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What is Noise?
Noise transmission paths
Sound waves travel from the source to the receiver via
multiple paths. Altering the paths of sound transmission
is a common way to control noise in architecture.
Flanking transmission of sound
Flanking transmission is the
propagation of sound wave via
building elements.
When sound strikes on a surface, part of the sound
reflects off the wall surface back into the space, and part An air gap can stop the
of it is transmitted through the wall to the space beyond. transmission of sound effectively.
[Discussion]
How is unwanted sound
transmitted in this diagram?
| Noise Control in Architecture | Lesson 1 - Sound transmission in architecture
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Noise Control through Architectural Design
Reducing Transmitted Sound Intensity Level
When sound wave travels through air or materials, the transmitted sound intensity level
is reduced due to sound power loss.
Almost every material exhibits sound insulating properties. They only vary in their level of
acoustic performance, which is measured in terms of the Sound Transmission Loss or
Sound Reduction Index.
Sound Reduction Index
When two partitions or sound barriers are
completely separated and
isolated from one another, their ability to
reduce sound is increased.
| Noise Control in Architecture | Lesson 1 – Noise Control through Architectural Design
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Noise Control through Architectural Design
Extended Knowledge
The Sound Reduction Index of a
material as it affects a specific
frequency of sound can be found
using the following equation:
Where,
SRI= Sound Reduction Index (dB)
M= The mass per unit area of the material (kgm -2); and
f =Frequency of the sound (Hz).
The sound insulation performance of any homogenous material depends
mainly on its mass.
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Noise Control through Architectural Design
Possible Perspectives
• Sound reduction required from the meeting room
= 45 - 35 dB = 10dB
• Sound reduction required from the nearby sports
courts = 70 – 25 dB = 45dB
The wall of the meeting room should have a Sound
Reduction Index ranging from 10 dB to 45 dB.
According to the graph of Sound Reduction Index, three
building materials could be suitable for the meeting
room:
• 50 mm Plastered Breeze Block (a light concrete
building block made with cinder aggregate)
• 9 mm Glass
• 0.7 mm Sheet Steel
After obtaining the data from an acoustic consultant,
architects decide what materials should be used for
the functions and aesthetics of the space.
Other considerations include structural tolerance,
environmental concerns and universal design for all
users.
Sound Reduction Index of common building materials
(Source: “Noise Control in Mechanical Services”, 1972)
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Noise Control through Architectural Design
[Discussion]
The school principal prefers using plywood as the wall surface.
He comments that a glass wall is not good for privacy but he wants to introduce natural lighting and ventilation
to the new meeting room.
What possible solution would you suggest?
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Noise Control through Architectural Design
Possible Perspectives
A double-leaf plywood wall could be constructed with a row of double-glazed operable
clerestory windows for natural lighting and ventilation.
Double-partition wall insulation
When two sound barriers are completely separated and
isolated from one another, sound insulating performance is
enhanced. Sound absorption materials like mineral wool
can be used to fill the cavity for extra sound insulation
against flanking transmission.
© NAP Acoustics (Far East) Ltd
Double-glazing
An operable double-glazed window provides
horizontally offset openings that allows natural
ventilation while preventing direct propagation of
traffic noise. The narrow path between the double
window panes dissipates sound energy and lowers
noise levels relatively.
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Noise Control through Architectural Design
Redirecting Sound away from Receivers
Artificial noise screen
Noise barriers can redirect the paths of noise away from receivers. They can be artificial (for example, a
wall) or natural (a forest).
One common application for noise barriers is to prevent traffic sounds from penetrating nearby
neighborhoods or habitats.
Sometimes noise barriers are integrated with the building design. Noise sensitive buildings like
residential blocks may be built above a podium or a shopping mall that inhibits the transmission of noise
to the apartments.
| Noise Control in Architecture | Lesson 1 – Noise Control through Architectural Design
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Noise Control through Architectural Design
[Discussion]
Can you identify the noise sources and barriers in the images and trace the sound transmission paths?
Mark them on the following picture.
| Noise Control in Architecture | Lesson 1 – Noise Control through Architectural Design
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Noise Control through Architectural Design
Case Study – Kwai Tsing Theatre
Isolating structure-borne noise from the building © WAAGNER-BIRO AG
Kowloon’s Kwai Tsing Theatre illustrates how architectural design can be used to protect
quiet spaces against airborne and structure-borne noises from inside and outside the
theatre. Its location next to the MTR railway and heavy traffic is particularly challenging given the
requirements of the theatre’s multifunctional spaces, which sometimes host simultaneous events.
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Noise Control through Architectural Design
Case Study – Kwai Tsing Theatre
Photographs showing how the springs integrate with the structure of Kwai Tsing Theatre; © VIPAC Engineers & Scientists (HK) Ltd
Springs placed on the pile caps of the building can absorb exterior structure-borne noise before it is
transmitted to the interior. Theatre and music rooms are built inside an isolated shield to reduce flanking
transmission of noise.
Noise-isolating springs c NAP Acoustics (Far East) Ltd
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Noise Control through Architectural Design
Case Study – Kwai Tsing Theatre
Improving the Sound Reduction Index of the Structure
The ceilings, walls and floors of the theatre are isolated from building structure by springs or resilient
pads. An air gap around the floating floors and suspended ceilings also improves the Sound
Reduction Index of the structure.
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Noise Control through Architectural Design
Case Study – Kwai Tsing Theatre
The air gap is the most important factor – increasing it (rather than increasing the mass of the
floors) would achieve greater reductions in noise as compared to increasing the mass of the
structure or the floating floor.
© VIPAC Engineers & Scientists (HK) Ltd
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Summary
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Noise means unwanted sound. It is subject to human perception.
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Sound Intensity Level is a scientific approach providing A logarithmic scale
is used to measure sound intensity (Wm-2), and is expressed as:
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Noise control in architecture is dealing two sources of noise: airborne and
structure-borne.
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Summary
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Two ways to control noise: reducing transmitted Sound Presure Level and
reddirecting sound transmission paths to the receivers.
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Sound Reduction Index is used for the purpose of choosing the appropriate
sound insulating performance for a building. It indicates the degree of sound
intensity reduction when a sound wave passes through a material.
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Noise barrier redirects noise transmitting paths to the receivers.
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