This document discusses principles of sound, acoustics, and noise. It covers topics such as the nature of sound including sound waves, sound levels measured in decibels, noise, and architectural acoustics. It provides information on measuring sound absorption coefficients of materials and factors that influence sound absorption. Design considerations for auditorium acoustics are also discussed.

1. SOUND,ACOUSTICS AND
NOISE
BSR 451
Environmental Science and Engineering Services I

2. PRINCIPLES OF SOUND

3. The Ear
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Shown is the external, middle and internal parts of the human ear.

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6. PRINCIPLES OF SOUND
THE ABILITIES OF SPEAKING AND
HEARING ARE VERY IMPORTANT
FACTORS IN OUR PERSONAL LIVES
AND IN OUR ENVIRONMENT.
AREAS SUCH AS MUSIC, SOUND
RECORDING AND REPRODUCTION,
TELEPHONY, ARCHITECTURAL
ACOUSTICS, AND NOISE CONTROL
ALSO HAVE STRONG ASSOCIATIONS
WITH OUR SENSATION OF HEARING
AND REQUIRE AN
UNDERSTANDING OF THE
PRINCIPLES AND EFFECTS OF
SOUND.
UNWANTED SOUND IN THE
ENVIRONMENT IS PERCEIVED AS A
NUISANCE AND CAN CAUSE
EMOTIONAL EFFECTS SUCH AS
ANNOYANCE, IRRITATION AND
SLEEP DISTURBANCE.
THE MAIN SOURCES OF
ENVIRONMENTAL NOISE ISSUES
ARE TRANSPORTATION NOISE,
INDUSTRIAL NOISE,
CONSTRUCTION NOISE, AND NOISE
FROM LEISURE AND
ENTERTAINMENT.

7. The measurement of noise
exposure is an important step
towards protecting people
from hearing damage and in
creating satisfactory
environments for living.
Good practice in the design of
buildings and the
construction of buildings
therefore involves a
consideration of the presence
of sound in the environment.

8. Topics of concern are:-
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8
Reduction of noise at
source
Exclusion of external
noise
Reduction of sound
passing between rooms
Quality of sound inside
rooms.

9. NATURE OF SOUND
Origin of Sound
Sound is a variation in the pressure of the air of a type which has an
effect on our ears and brain. These pressure variations transfer energy
from a source of vibration that can be naturally-occurring, such as by the
wind or produced by humans such as by speech. Sound in the air can be
caused by a variety of vibrations, such as the following:-
• Moving objects - examples include loudspeakers, guitar strings, vibrating walls and
human vocal chords.
• Moving air - examples include horns, mechanical fans and jet engines.
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9

10. Wave Motion
• The mechanical vibrations of sound move forward
using wave motion. This means that, although the
individual particles of material such as air molecules
return to their original position, the sound energy
obviously travels forward. The front of the wave
spreads out equally in all directions unless it is affected
by an object or by another material in its path.
• The sound waves can travel through solids, liquids and
gases, but not through a vacuum.

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12

13. SOUND
WAVES

14. Wavelength (λ)
Wavelength is the
distance between
any two repeating
points on a wave.
Unit metre (m)

15. Frequency (ƒ)
Frequency is the
number of cycles
of vibration per
second. Unit hertz
(Hz)

16. Velocity (v)
• Velocity is the distance moved per second in a fixed
direction. Unit metres per second (m/s)
• For every vibration of the sound source the wave
moves forward by one wavelength. The number of
vibrations per second therefore indicates the total
length moved in 1 second; which is the same as
velocity.

17. v = ƒ x λ
v = velocity in m/s
ƒ = frequency in Hz
λ = wavelength in m
Worked example
A particular sound wave has a frequency of 440 Hz and a velocity of
340 m/s. Calculate the wavelength of this sound.
Know
v = 340 m/s, ƒ = 440 Hz, λ = ?
Using formula for velocity and substituting
v = ƒ x λ
340 = 440 x λ
λ = 340/440
= 0.7727
So wavelength = 0.7727 m
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18. Velocity of Sound
• The velocity of sound is independent of the rate at which the
sound vibrations occur, which means that the frequency of a
sound does not affect its speed.
• Also unaffected by variations in atmospheric pressure such
as those caused by the weather.
• But, is affected by the properties of the material through
which it is travelling, gives an indication of the velocities of
sound in different materials.
• Sound travels faster in liquids and solids than it does in air
because of the effect of density and elasticity of those
materials.
• The particles of such materials respond to vibrations more
quickly and so convey the pressure vibrations at a faster rate.
• For example, steel is very elastic and sound travels through
steel about 14 times faster than it does through air.

19. The cowboy will
hear the train
noise
via the rails before
he hears it through
the
air

20. Velocity of
Sound

21. Frequency of Sound
• If an object that produces sound waves vibrates 100 times
a second, for example, then the frequency of that sound
wave will be 100 Hz. The human ear hears this as sound of
a certain pitch.
• Pitch is the frequency of a sound as perceived by human
hearing.
• The frequency range to which the human ear responds is
approximately 20 to 20 000 Hz.
• Most sounds contain a combination of many different
frequencies and it is usually convenient to measure and
analyse them in ranges of frequencies.

22. The frequency
range to which
the human ear
responds is
approximately
20 to 20 000 Hz.

23. Illustration based
on figure in 'Noise
Control - A Guide
for Workers and
Employers' US
Department of
Labor, 1980
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24. SOUND
LEVELS
The strength or 'loudness' of a sound depends upon
its energy content and this energy affects the size of
the pressure variations produced.
Measurement
To specify the strength of a sound it is usually
easiest to measure or describe some aspect of its
energy or its pressure. Even so, sound does not
involve large amounts of energy and its effect
depends upon the high sensitivity of our hearing.
Sound power
Sound Power (P) is the rate at which sound energy is
produced at the source. Unit watt (W)
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26. Thresholds
The weakest sound that the average human ear can
detect is remarkably low and occurs when the membrane
in the ear is deflected by a distance less than the
diameter of a single atom.
Threshold of hearing
Is the weakest sound that the average human ear can
detect.
The value of the threshold varies slightly from person to
person but for reference purposes it is defined to have
the following values at 1000 Hz.
Io = 1 x I0ֿ12 W/m2 when measured as intensity
po= 20 x 10 ֿ 6 Pa (pascal) when measured as pressure
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27. • The sound intensity of the
threshold of hearing (the
quietest sound we can
hear) is 0.00000000001
watts/m2 (often written
I0 ֿ
12W/m2 )

28. Threshold
of pain
The threshold of pain has the following approximate values.
I = 100 W/m2 Or p = 200 pa (pascal)
Very strong sounds become painful to the ear. Excessive sound
energy will damage the ear mechanism and very large pressure
waves will have other harmful physical effects, such as those
experienced in an explosion.
Is the strongest sound that the human ear can tolerate.

29. The sound
intensity at the
threshold of
pain is about
100 watts/m²

30. THRESHOLD OF PAIN

31. Decibels (dB)
• For practical measurements of sound strength it is
convenient to use a decibel scale based on constant
ratios, a scale which is also used in some electrical
measurements.
• The Decibel (dB) is a logarithmic ratio of two
quantities.

32. The decibel (dB) is
calculated by the following
formulas using either values
of sound intensity or sound
pressure. Velocity is
proportional to the
pressure squared.

33. In the measurement of sound levels
the decibel ratio is always made with
reference to the standard value for
the threshold of hearing.
This produces a scale of numbers
that is convenient and gives a
reasonable correspondence to the
way that the ear compares sounds.
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35. Approximate
Sound Levels
in Decibels
(dB)
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Police siren: 118
Rock band, disco: 115
Missing muffler: 115
Hole(s) in muffler: 111
Tailpipe damage: 109
Circular saw: 107
Hole/break in pipe from engine to muffler: 105
Internal muffler deterioration: 104
Heavy truck at 90 feet (40 mph): 99
Power mower: 92
Freight train at 50 feet: 88
Printing press: 80
Vacuum cleaner: 74
Busy street traffic: 70
Air-conditioning unit: 60
Interior of a quiet car: 50
Private office: 41
Library: 33
Threshold of hearing: 0
Maximum allowable sound level from car exhaust under city's noise control ordinance: 96

36. FACTS
Sound at 155 decibels
can burn the skin.
Sound at 180 decibels
can kill.

37. The figure shows the total
range of sound levels in
decibels between the two
thresholds of hearing and
gives typical decibel values
of some common sounds.
Precise values would
depend upon the
frequencies contained in
the sounds and the
distances from the source.

38. Changes in
sound
levels
• The smallest change in sound level that the human ear can detect
is 1 dB, although a 3 dB change is considered the smallest difference
that is generally significant. A 10 dB increase or decrease makes a
sound seem approximately twice as loud or half as loud, as shown in
table below.
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40. NOISE

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43. ACOUSTICS

44. ACOUSTICS
• The term 'acoustics' can be
used to describe the study of
sound in general
• It is the interdisciplinary
science that deals with the
study of all mechanical waves
in gases, liquids, and solids
including topics such as
vibration, sound, ultrasound,
and infrasound.

45. THREE CATEGORIES OF ACOUSTICS
Physical Acoustics
Acoustics
Biological Acoustics Acoustical Engineering
Aero acoustics
General Linear acoustics
Non-Linear acoustics
Structural acoustics and vibration
Under water sound
Psychoacoustics
Bioacoustics
Musical acoustics
Physiological acoustics
Speech Communication
Acoustical Measurement and
Instrumentation
Acoustical Signal Processing
Architectural acoustics
Transduction
Environmental acoustics
Ultrasonic
Room Acoustics

46. Architectural
Acoustics :
• It is also known as room
acoustics and building
acoustics, is the science
and engineering of
achieving a good sound
within a building and is a
branch of acoustical
engineering.

47. • The study of acoustics revolves around the generation, propagation
and reception of mechanical waves and vibrations.
Cause
Generating
Mechanism
(transduction)
Acoustic Wave
Propagation
Reception
(transduction)
Effect
The steps shown in the above diagram can be found in any
acoustical event or process.

48. Applications
and relations
of Acoustics

49. An Analysis of Different
Parameters of Architectural
Buildings
• There are many parameters related with architectural
buildings. Some parameters are pointed out below:-
• The model theory
• The geometric theory
• The theory of Sabine & reverberation
• Acoustic intensity and decibel
• Boundary conditions
• Noise effect
• Loudness
• Focussing
• Echelon effect
• Extraneous noise
• Resonance
• Temperature
• Absorbing material
• Pitch

50. Study and Measurement of Sound
Absorption Coefficients of
Materials
• Performance of sound absorbing materials is defined by a set of
experimentally determined constants i.e. absorption coefficient,
reflection coefficient, acoustic impedance, propagation constant,
normal reduction coefficient, and transmission loss.
• The sound absorption coefficient of a surface is defined as the ratio
of the sound energy absorbed by the surface to that falling on it.
• Absorption coefficient of materials vary at different frequencies.
• Absorption of sound by materials is due to the porosity,
compressibility, and elasticity. The materials absorb sound when
the sound waves are dissipated into heat by friction in the narrow
pores.
• Some of the materials are compressible, such as hair felt, carpets,
etc. some absorb sound by vibrating, as is probably the case with
thin glass, wood, and suspended plaster ceilings.

51. Factors Influencing
Sound Absorption
• Fiber Size
• Airflow Resistance
• Porosity
• Tortuosity
• Thickness
• Density
• Compression
• Surface Impedance
• Placement / Position of Sound Absorptive

52. A chart of the absorption coefficient of material has
been shown at different frequency levels

53. ACOUSTIC
PRINCIPLES

54. ACOUSTIC PRINCIPLES
• General requirements
• The detailed acoustic requirements for a particular room depend
upon the nature and the purpose of the space, and the exact
nature of a 'good' sound is partly a matter of personal preference.
• The general requirements for good acoustics are as follows:-
• Adequate levels of sound
• Even distribution to all listeners in the room
• Rate of decay (reverberation time) suitable for the type of room.
• Background noise and external noise reduced to acceptable
levels.
• Absence of echoes and similar acoustic defects.

55. AUDITORIUM
• An auditorium is a room,
usually large, designed to be
occupied by an audience.
The acoustic design of the
auditoria is particularly
important and detailed
acoustic requirements vary
with the purpose of the
space.

56. TYPES AND PURPOSES
OF AUDITORIUM
• A. SPEECH
• The overall requirement for good reception of
speech is that the speech is intelligible.
• This quality will depend upon the power and
the clarity of the sounds.
• Examples of auditoria that are specially used
for speech are conference halls, law courts,
theatres, and lecture rooms.

57. • B. MUSIC
• There are many more acoustic requirements for
music than for speech.
• Music consists of a wide range of sound levels and
frequencies which all need to be heard. In addition,
some desirable qualities of music depend upon the
individual listener’s judgment and taste.
• These qualities are difficult to define but terms in
common use include 'fullness' of tone, 'definition'
of sounds, 'blend' of sounds, and 'balance' of
sounds. Examples of auditoria designed exclusively
for music are concert halls, opera houses, recording
studios, and practice rooms.

58. • C. MULTI-PURPOSE
• There are some conflicts between the real
acoustic conditions for music and for
speech.
• Compromises must be made in the design
of auditoria for more than one purpose
and the relative importance of each
activity needs to be decided upon.
• Churches, town halls, conference centers,
school halls, and some theatres are
examples of multi-purpose auditoria.

60. DESIGN CONSIDERATION

61. Sound sources
• Each of the sound sources will interact with the
acoustical envelope. If the envelope has hard,
reflective surfaces, sounds will bounce about or
reverberate aid possibly even be amplified until
they die out.
• A space with a considerable number of sound-
reflective surfaces will have a long
"reverberation time" and sound like a room
with echoes.
• If the interior envelope has sound-absorptive
surfaces, the sound sources will be quieted and
have a short reverberation time.
• Rooms with a short reverberation time are
preferred for ease in communication

62. Interior Acoustical
Envelope
• An interior acoustical envelope usually consists of hard surface
materials that readily reflect sounds.
• Examples of highly reflective materials include gypsum wallboard,
plaster, glass, wood, and ceramic surface.
• Examples of materials that have good sound absorption
properties include room decorations and furnishings such as
carpet and pad, lined draperies, acoustical ceiling materials,
acoustical wall coverings, upholstered furniture, and pillows.

63. ACOUSTICAL
MATERIAL
• Materials that are good sound barriers are impervious, hard,
and heavy.
• Materials that are good sound absorbers are soft, fuzzy, and
porous.
• As a comparison, materials that are good sound barriers will
also resist water and air passage (glass and concrete for
example), while materials that are good sound absorbers are
much like a sponge.

64. Room Acoustics And Sound Isolation
• There is an important distinction between room acoustics and sound
isolation.
• Sound isolation - is the control of the sound transmission between adjacent
spaces.
• Room acoustics - has the goals of noise reduction and reduced
reverberation (echoes) for good hearing conditions within a space.
• Sound reflections within a room can be controlled with a combination of
materials such as an acoustical ceiling, drapes, thick carpeting, upholstered
furniture, and sound-absorbing wall treatments.
• These materials absorb the sound upon impact and thereby reduce the
reverberation within the space.

65. Acoustics within room

67. Sound
Transmission
• Acoustic transmission is the transmission of
sounds through and between materials,
including air, wall, and musical instruments.

69. SOUND
REDUCTION
INDEX &
ABSORPTION
COEFFICIENT
According to
ISO717 & ISO
11654

70. Reverberation Time
(RT)
• If sound in a room is reflected from several surfaces it will
reach the receiver at different times and in the worst cases
an echo is set up.
• The reverberation time is a standard to indicate the time
taken for a sound to decay by 60 decibels. For example, if
the sound in a room took 10 seconds to decay from 100dB
to 40dB, the reverberation time would be 10 seconds.
• RT - time taken for the sound intensity to die away to one
millionth (-60dB) of its original intensity, the symbol is ‘t’
and the units are in seconds.

71. • The table below shows some typical reverberation times , (s)
Use
Small Rooms
750 m3
Medium Rooms
750 –7500 m3
Large Rooms
Over 7500 m3
Speech 0.75 0.75 - 1.00 1.00
Multi-purpose 1.00 1.00 - 1.25 1.00 - 2.00
Music 1.50 1.50 - 2.00 2.00 or more
Reverberation
Times, (S)

72. Sabine Formula
• Sabine devised an equation that relates
reverberation time ‘t’ with volume ‘V’ of a
room and the total absorption ‘A’ of the room.
• The absorption ‘a’ is found by obtaining the
sound absorption coefficient (a) for each
material in the room and multiplying it by the
areas (s) of each material and adding all the
absorption together.

73. • Sound absorption coefficient
- used to evaluate the sound
absorption efficiency of
materials.
• It is the ratio of absorbed
energy to incident energy and
is represented by α.
• If the acoustic energy can be
absorbed entirely, then α = 1.
ITEM
ABSORPTION COEFFICIENT
125 Hz 500 Hz 2000 Hz
Air 0 0 0.007
Audience (padded seats)
per person
0.17 0.43 0.47
Seats (padded) per seat 0.08 0.16 0.19
Brickwork 0.02 0.02 0.04
Floor tiles (hard) 0.03 0.03 0.05
Plaster 0.02 0.02 0.04
Window (5mm) 0.02 0.01 0.05
Fibreboard with space behind 0.30 0.30 0.30
Suspended plaster-board ceiling 0.20 0.10 0.04
Ply panel over air space with
absorbent
0.40 0.15 0.10
Curtains - heavy 0.10 0.40 0.50
Sound Absorption
Coefficient

74. Partition Insulation
The amount of Sound reduction in decibels (dB) through a
partition can be defined as the Sound Reduction Index.

75. 75

76. Sound Reduction
Index (S.R.I)
• A formula for Sound Reduction Index

77. BSR451 – NOISE CONTROL
DR JULAIDA KALIWON

78. WHAT IS
NOISE
CONTROL ?
• By definition - Is the technology of obtaining an
acceptable noise environment consistent with
economic and operational considerations.
• The term "acceptable noise environment" ………
usually no unique answers.
• Acceptable to whom, and under what conditions?
Acceptable to an individual, to a group of people, to
an entire community, or to some percentage of a
group or community? Acceptable at what time of
day or night?
• The acceptability of a noise environment usually is
different at different times during a 24-hour period.
• For example, in a residential area, during the night
when people are sleeping, it is usually required that
conditions be quieter than during daylight hours.
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79. THE IMPORTANCE OF NOISE CONTROL
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Many businesses and industries are
spending considerable amounts of money
annually to achieve conditions of quiet.
People are usually annoyed by noise.
They are distracted by it.
Noise is considered a public nuisance.

80. Source: Health and Safety Executive for the UK
Noise Exposure
Of
Construction
Activities

81. The Impact Of Noise In
Modern Society
• In modern society, problem of great economic
importance. When the noise level in business
offices is high enough to interfere with
speech communication, office efficiency may
be reduced, resulting in economic losses.
• Another example of the economical
importance of noise is the relationship
between noise and property values. The
construction of a major roadway through a
residential area may reduce the value of the
adjacent land for residential housing because
of increased noise levels.
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82. • Poor understanding of the techniques
used to control sound leads to incorrect
and wasted efforts.
• In solving a specific noise problem, it is
usually advantageous to :-
1. Analyze the problem
2. Determine the most economic
solution
3. Apply the noise reduction techniques
required for its solution
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83. NOISE CONTROL METHODS IN
BUILDINGS
• Application methods of noise control should be applied in
the design of a new building to ensure satisfactory
conditions of quiet, and in an existing building to reduce
existing noise levels within it. Such methods, may be
classified as :-
1. Control of noise at the source
2. Control of noise along its transmission path from
the source to the listener by increasing the
attenuation (is the reduction in amplitude and
intensity of sound) between the source and the
listener
3. Control of noise by providing the listener with
some form of noise protection
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84. ROOM ACOUSTIC

85. WHAT IS ROOM ACOUSTICS?

86. Room Acoustics

87. • The acoustic quality of sound in a room can
affect the way that people judge noise
levels.
• The sound quality of a large auditorium,
such as a concert hall, can be difficult to
perfect and acoustics has sometimes been
described as an 'art' rather than a 'science'.
• But, as with thermal and visual comfort,
there are technical properties that do affect
our perception, and these make the best
starting point for designing or improving
the environment.

88. NOISE CONTROL
Sources of Noise in Buildings How to avoid turbulence (Induce Noise)

89. Noise Transmission in Buildings
• The block labeled source may
represent a single source or
several sources of noise. As
indicated, noise from the source
is communicated through the
structure along one or more
transmission paths. The listener
usually represents one person
or a group of people.
• Which of these methods, or
combination of methods, is
most advantageous depends on
the required amount of noise
reduction, on economic
conditions, and on operational
considerations.
• The relative benefit to be
gained from the application of
each method may be evaluated
and compared with its
respective cost.

90. Noise Transmission in Buildings
90

91. Acoustic screens and
barriers
• Devices to deflect and absorb sound waves can be effective if
they are placed close to the source of sound, or close to the
recipient of the noise.

92. Control of Noise
at Its Source
• To control noise at its source:-
• Reduce the amplitude of motion
of the source. For example, if the
noise source is a vibrating panel
of a washing machine, the
magnitude of its vibration may be
reduced by applying a vibration-
damping material on the panel's
surface or by modifying the
panel's stiffness, mass, or size.
• Enclose the noise source within
solid, heavy walls which are lined
with sound absorptive material.

93. MATERIAL
USED IN NOISE
CONTROL
• Vibration-damping material

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95. 12/31/2023 95

96. 12/31/2023 96

97. METHOD IN REDUCING
NOISE
• Mount the noise source on
vibration isolators instead of
directly on the floor.
• Install a resilient floor
covering or a floating floor (a
"floating floor" is a floor that
is supported by the building
structure but is completely
isolated from it.)
• Comprises a three-ply
acoustic base mat laid over
with a dense sound check
layer. The finish floor surface
is a 12mm tongue & grooved
floating floor panel

98. METHOD IN
REDUCING NOISE
• Vibration Isolators

99. 99

100. Control of
Noise along
Its
Transmission
Path
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To control noise along its transmission path
the noise source and listener :-
Position the building on its site so as to
minimize noise control measures that would
otherwise be required. For example:
• Maximize the distance between the building and a
nearby highway.
• Orient the building so that the building (and nearby
buildings) shield areas where quiet is required.
• Use the natural terrain, road cuts, embankments, and
artificial barriers to provide additional shielding.
• Orient buildings to avoid reflections of street noise
into areas where quiet is required.

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102. Control Noise Along Its Transmission Path
12/31/2023 102

103. Control
of
Noise
along
Its
Transmission
Path
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103
Plan the location of rooms within the building to
minimize noise control measures that would
otherwise be required. For example:
• Locate rooms that contain significant noise sources as far as possible
from rooms in which quiet conditions are desired.
Plan
Seal all openings along airborne paths between the
noise source and the listener. For example:
• Seal cracks and openings around conduits, pipes, or ducts that
penetrate walls to prevent the transmission of sound along these
paths.
Seal

104. Control of Noise along Its Transmission Path
• Improve the sound insulation provided by partitions. For
example:
• Add a resiliently-supported gypsum board wall surface
to an existing wall.
• Increase the mass of the existing wall.
• Add a second leaf to an existing single-leaf wall.
• Replace existing single glazing with double glazing.
• Install seals (usually in the form of gaskets) around the
perimeters of doors.
• Improve the sound insulation of an existing floor slab. For
example:
• Provide a resiliently hung ceiling supported from the
structural slab above.

105. Control of Noise along
Its Transmission Path
• Impede the transmission of structure borne noise by
breaking the path along which it is communicated., For
example:
• Use building expansion joints to impede the
transmission of noise through a building structure by
locating the sources of noise (such as elevators,
mechanical equipment, water lines, toilets, and heavy
transformers) on one side of the expansion joint and
locating the areas where quiet conditions are essential
on the other side of the expansion joint.
• Install additional sound-absorptive materials in rooms
to lower the noise level
• Install partial-height partitions where fully partitioned
rooms are impractical.

106. Control of Noise
at the Listener
• To control noise at the listener:
• Furnish the listener with a
booth or partial enclosure in
which work.
• Furnish the listener with
earplugs.

107. HOW MUCH NOISE
REDUCTION IS REQUIRED
1. In general, the following steps may be taken to determine the
amount of noise reduction required for the solution of a specific
noise problem:
• Evaluate the noise environment under existing or expected
conditions.
• Existing noise conditions may be determined from
measurements which provide data that are statistically
significant. This process requires the appropriate selection of the
noise measurement equipment, accurate calibration of the
equipment, and correct use of this equipment.
• Such procedures often are set forth by voluntary or mandatory
standards, in governmental regulations, in industrial association
codes, or in requirements for environmental impact statements.
• Expected noise conditions usually can be estimated from
empirical engineering formulas or from data derived from similar
existing projects.

108. HOW MUCH
NOISE
REDUCTION
IS REQUIRED
2. Determine what noise level is acceptable
or what noise criterion is to be satisfied.
• A noise criterion is defined as a standard or rule
for judging the acceptability of noise levels
under different conditions and for various
purposes.
3. Obtain the difference between the noise
level in Step 1 and the noise level in Step
2.
• This difference represents the noise reduction
that must be provided to obtain an acceptable
environment.

109. HOW MUCH
NOISE
REDUCTION IS
REQUIRED
Example:

110. PERSONAL
PROTECTION
• If other methods fail to reduce the noise energy
reaching the ear, then individual hearing needs to
be protected by wearing hearing defenders over
the ears.
• The two broad types of ear protectors available
are ear plugs inserted in the ear canal and
earmuffs which cover the entire ear.
• When choosing and using hearing defenders the
following properties should be considered:
• sufficient level of protection
• sufficient comfort to wear for as long as
required
• durability for as long as required
• hygienic in practical operation.
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111. Active Noise
Reduction
(ANR)
• A sound wave can be neutralized by an identical
wave that, if it is half a wavelength out of phase,
provides equal and opposite compressions and
rarefactions.
• Equipment is available that rapidly analyses a
sound and uses a speaker to produce appropriate
'anti-noise' which lowers the sound level.
• ANR techniques work best for relatively constant
sounds at lower frequencies. Current
applications include earmuffs, headsets, confined
machinery spaces, industrial chimneys.
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112. 12/31/2023 112

113. Practical Sound Sources
• It is important to distinguish between airborne and impact
sound because the best methods of controlling them can
differ.
• A single source of noise may also generate both types of
sound, so the definition of airborne and impact sound must be
applied to the sound which is being heard in the receiving
room. For example, footsteps on a floor would be heard mainly
as impact sound in the room below but heard as airborne
sound in the room above.
• Sound can also pass into a receiving room by flanking
transmission. These indirect sound paths can be numerous and
complex.
• The effect of flanking transmissions increases at high levels of
sound insulation and often limits the overall noise reduction
that is possible.
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114. Absorption And Insulation
The techniques used to control sound are described by some terms that
may appear to be interchangeable but are, in fact, very different in their
effect. Poor understanding of these terms leads to incorrect and wasted
efforts in the control of sound.
Sound insulation
• Sound Insulation is the reduction of sound energy transmitted into an
adjoining air space.
• Insulation is the most useful method for controlling noise in buildings
and is discussed in the next section.
Sound absorption
• Sound Absorption is a reduction in the sound energy reflected by the
surfaces of a room.
• Absorption usually has little effect on noise control but has an
important effect on sound quality – which is related to acoustics.

115. SOUND ABSORPTION
• It can be shown by calculation that if the amount of
absorption in a room is doubled then the sound energy in
the room is halved, but the sound level drops by only 3 dB.
Such a change in absorption may, however, make a
difference to the subjective or apparent sound level in the
room because this is also influenced by the acoustic quality.
• Sound absorption can also be useful in the control of noise
that spreads by reflections from the ceiling of offices and
factories, or by multiple reflections along corridors or
ducts.
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116. SOUND INSULATION
• Insulation is the principal method of controlling both
airborne sound and impact sound in buildings.
• The overall sound insulation of a structure depends upon
its performance in reducing the airborne and impact sound
transferred by all sound paths, direct and indirect.
• The assessment of sound insulation initially considers one
type of sound transfer at a time.

117. NOISE TRANSMISSION
• In both new and old
buildings, the
transmission of impact
sound such as footfalls
or moving furniture can
become quite a
nuisance. This is
particularly so in the
modern apartment
building, especially
where designers must
use ever more slender
floor slabs to keep
building heights lower.

118. NOISE INSULATION
• Insulation reduces the level of both exterior and
interior noise by preventing transmission of exterior
sounds to the interior of the building, and absorbing
reverberating sounds within the building.

119. NOISE
INSULATION

120. • It is also common to see
parallel sound walls on
roadways. Reflective parallel
sound walls often reduce the
wall's acoustical performance.
The net result is less than
optimal performance and
increased noise levels on and
adjacent to the roadway.
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121. Noise Pollution
1. Noise pollution (or environmental noise in
technical venues) is displeasing human or
machine created sound that disrupts the
environment. The dominant form of noise
pollution is from transportation sources,
principally motor vehicles. The word "noise"
comes from the Latin word nausea meaning
"seasickness", or from a derivative (perhaps Latin
noxia) of Latin noceō = "I do harm", referring
originally to nuisance noise.
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sound tube
Noise barrier earth berm
noise abatement wall

122. Noise and Sound Insulation

123. Noise And
Sound
Insulation
• Noise is unwanted sound. The results of national surveys of
typical exposure to noise show that over 50% of the population
are exposed to day-time noise levels that exceed the World
Health Organisation (WHO) ratings for significant community
annoyance.
• Other surveys report that around 50% of people find their home
in some way unsatisfactory because of noise intrusion. These
results include people living in new homes built to modern
building codes which require certain standards of noise control.
• A satisfactory environment of sound quality therefore needs to
be a major consideration when we create our built
environment.
• The environmental and social definitions of noise take account
of the effect of the sound rather than the technical nature of
the sound.
• So even if a sound consists of the finest music, it can be
considered as noise if it occurs in the middle of the night.
12/31/2023

124. Detrimental Effects
• The following are some of the detrimental effects that noise
can have on people and their environment.
• Hearing loss - excessive exposure to noise causes loss of
hearing.
• Quality of life - noisy environments, such as near busy roads or
airports, are considered unpleasant and undesirable.
• Interference - interference with significant sounds such as
speech or music can be annoying and, in some situations,
dangerous.
• Distraction - distraction from a particular task can cause
inefficiency and inattention, which could be dangerous.
• Expense - the measures needed to control excessive noise are
expensive. Businesses may also suffer loss of revenue in a
noisy environment.

125. Measurement Of Noise
• The acceptance of noise by people depends upon personal
hearing sensitivity and personal preferences, so individuals
vary widely in their response to the same level of noise,
even when it arises from the same source.
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126. The Acceptance Of Noise
The acceptance of noise is also affected by the external factors such as:-
• Type of environment - acceptable levels of surrounding noise are
affected by the type of activity. A library, for example, has
different requirements to those for a workshop.
• Frequency structure - different noises contain different
frequencies and some frequencies are found to be more
annoying or more harmful than others. For example, the high
whining frequencies of certain machinery or jet engines are
more annoying than lower frequency rumbles.
• Duration - a short period of high-level noise is less likely to annoy
than a long period. Such short exposure also causes less damage
to hearing.

127. Noise Annoyance
• Noise annoyance is ‘a feeling of displeasure evoked by
noise’ (the World Health Organisation)
• Although individuals vary in their response to a certain level
of noise, when a large number of people are exposed to the
same sources of noise the average or community response
is relatively stable. It is therefore possible to establish the
community average degree of annoyance associated with
long-term average noise exposure.
• The concept of annoyance is well established for identifying
the noise impacts from roads, railways, airports and
building sites.
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128. NOISE TRANSFER • Noise is transferred into buildings and
between different parts of buildings by
means of several different mechanisms. It
is necessary to identify the types of
sound involved as being of two main
types:
• Airborne Sound
• Impact sound
• Airborne Sound is sound which travels
through the air before reaching a
partition.
• The vibrations in the partition under
consideration must be started by sound
that has travelled through the air.
• Typical sources of airborne sound include
voices, radios, musical instruments,
traffic and aircraft noise.

129. Airborne & Impact
Sound Transmission
• Impact Sound (structure-borne
sound) is sound which is generated
on a partition.
• Typical sources of impact sound
include footsteps, slammed doors
and windows, noisy pipes and
vibrating machinery.
• A continuous vibration can be
considered as a series of impacts.
• Notice that such impact sound will
normally travel through the air to
reach our ear, but it is not the same
as airborne sound.

130. THANK YOU