Noise pollution is unwanted or disturbing sound produced by human activities that interferes with normal activities like sleeping or conversation. The document discusses methods of noise reduction like using absorptive materials and increasing transmission loss. It also describes common noise measuring equipment like sound level meters, octave band analyzers, and noise dosimeters that are used to measure sound pressure levels and exposure at various frequencies. The aim is to study techniques for noise reduction and understand how equipment is used to measure noise.

1. Noise
POLLUTION
Presented By :-
SATPAL
Environmental Engineering
Government Engineering
College
2011-2012

2. INTRODUCTION
 Noise pollution is the unwanted
or disturbing sound which are
produced by human activities.
 Sound becomes unwanted when
it either interferes with normal
activity such as sleeping ,
conversation or disrupts or
diminishes one’s quality of life .

3. AIM
NOISE REDUCTION
&
STUDY OF
NOISE MEASURING
EQUIPMENTS

4. What is noise reduction ?
Noise reduction is the process
of removing noise from
a signal

5. ABSORPTIVE MATERIAL
 Hard rigid non-porous surfaces like
glass, marble or concrete, provide
the least absorption and are thus the
best reflectors.
 Soft porous surfaces and those which
can vibrate absorb more of the sound

6. The amount of sound absorbed is
proportional to the area of the
material concerned
 If we say
A= Area of exposed material
S = sound absorbed
then equation of sound
absorbed is
S = aA

7. Absorption Coefficient
 In equation S=aA
“a” is called absorption
coefficient
 a = amount of sound absorbed by a material
sound energy arriving at the surface
The Absorption Coefficient is a
number always less than 1

8. Floor Materials
125
Hz
250
Hz
500
Hz
1000
Hz
2000
Hz
4000
Hz
concrete or tile 0.01 0.01 0.15 0.02 0.02 0.02
linoleum/vinyl tile on concrete 0.02 0.03 0.03 0.03 0.03 0.02
wood on joists 0.15 0.11 0.10 0.07 0.06 0.07
parquet on concrete 0.04 0.04 0.07 0.06 0.06 0.07
carpet on concrete 0.02 0.06 0.14 0.37 0.60 0.65
carpet on foam 0.08 0.24 0.57 0.69 0.71 0.73

9. Seating Materials
125
Hz
250
Hz
500
Hz
1000
Hz
2000
Hz
4000
Hz
fully occupied - fabric upholstered 0.60 0.74 0.88 0.96 0.93 0.85
occupied wooden pews 0.57 0.61 0.75 0.86 0.91 0.86
empty - fabric upholstered 0.49 0.66 0.80 0.88 0.82 0.70
empty metal/wood seats 0.15 0.19 0.22 0.39 0.38 0.30

10. Wall Materials
125
Hz
250
Hz
500
Hz
1000
Hz
2000
Hz
4000
Hz
Brick: unglazed 0.03 0.03 0.03 0.04 0.05 0.07
Brick: unglazed & painted 0.01 0.01 0.02 0.02 0.02 0.03
Concrete block - coarse 0.36 0.44 0.31 0.29 0.39 0.25
Concrete block - painted 0.10 0.05 0.06 0.07 0.09 0.08
Curtain: 10 oz/sq yd fabric
0.03 0.04 0.11 0.17 0.24 0.35
molleton
Curtain: 14 oz/sq yd fabric
molleton
0.07 0.31 0.49 0.75 0.70 0.60
Curtain: 18 oz/sq yd fabric
molleton
0.14 0.35 0.55 0.72 0.70 0.65
Fiberglass: 2'' 703 no airspace 0.22 0.82 0.99 0.99 0.99 0.99
Fiberglass: spray 5'' 0.05 0.15 0.45 0.70 0.80 0.80

11. Miscellaneous Material
125
Hz
250
Hz
500
Hz
1000
Hz
2000
Hz
4000
Hz
Water 0.008 0.008 0.013 0.015 0.020 0.025
People (adults) 0.250 0.350 0.420 0.460 0.500 0.500

12. TRANSMISSION LOSS
Transmission Loss (TL)
measures the performance of a
building material (or
construction assembly) in
preventing airborne sound
transmission. This measure
VARIES when tested at
different frequencies, shown
over 1/3 octave intervals.

13. The term Transmission Loss (TL), or more
commonly Sound Reduction Index
(SRI) are used to describe the reduction in
sound level resulting from transmission
through a material. This is given by:
SRI = 10 log (Wsource / Wreceiver) = 10 log (1/t)
= -10 log (t)
the transmission coefficient (t) for
partition is
t = Wreceiver
Wsource

14.  Greater the mass, the less sound is
transmitted through the barrier .

15. NOISE ISOLATION CLASS
 The Noise Isolation Class (NIC)
measurement was carried out
according to ASTM E-336 'Testing
Method for Measurement of
Airborne Sound Insulation in
Buildings' and the calculation was
carried out according to ASTM E-
413.

16.  NIC of the test specimen was
determined by comparing the
noise levels sampled inside the
source and receiving rooms
between which the test specimen
separating them .
 The NIC rating of an element is
determined by plotting the 1/3
octave band of the element and
comparing it with the NIC
contour.

17. NIC of the test specimen was determined by
comparing the noise levels sampled inside
the source and receiving rooms between
which the test specimen separating them.
Sound measurement was carried out inside
the two rooms.

18. VIBRATION ISOLATION
 Vibration isolation is the process
of isolating an object, such as a
piece of equipment, from the
source of vibrations.

19. VIBRATION
ISOLATION
ACTIVE
ISOLATION
PASSIVE
ISOLATION

20.  Passive vibration isolation systems
consist essentially of a
mass, spring and damper (dash-pot )
 Active vibration isolation systems
contain, along with the spring,
a feedback circuit which consists of
a piezoelectric accelerometer, a
controller, and
an electromagnetic transducer.

21.  The acceleration (vibration) signal
is processed by a control circuit
and amplifier. Then it feeds the
electromagnetic actuator, which
amplifies the signal.
 As a result of such a feedback
system, a considerably stronger
suppression of vibrations is
achieved compared to ordinary
damping

22. ACTIVE NOISE CONTROL
 Also known as Noise cancellation
or Active noise reduction.
 Method of reducing unwanted
sound .

23. Noise Source
Anti Noise
Resulting Noise
source

24. NOISE MEASURING
EQUIPMENTS
1. Sound Level Meter
2. Octave Band Analyzer
3. Statistical Analyzer
4. Noise Average Meter

25. Sound
Level
Meter

26. Sound Level Meter
(SLM)
 Sound level meter measure sound pressure
level .
 The standard SLM is more correctly
called an exponentially averaging sound
level meter as the AC signal from the
microphone is converted to DC by root
mean square (RMS)

27.  The SLM consists of a microphone,
electronic circuits and a readout
display.
 In the beginning sound level
meters were very expensive,
heavy and didn't do very much

28.  They were effectively
a microphone and a
voltmeter with a 1
second [SLOW] time
constant to slow
down the meter
fluctuations, so you
could average them
by eye

29.  The microphone can
be compared to the
Hi-Fi loudspeaker,
one converts sound
waves into electrical
signals and the other
converts electrical
signals back into
sound waves

30. OCTAVE BAND
ANALYZER

31.  It determine the adequacy of
various types of frequency-dependant
noise controls.
 Octave band measurement is used
when the frequency composition
of a sound field is needed to be
determined

32. Most octave-band filter sets
provide filters with the
following center frequencies:
 31.5, 63, 125, 250, 500, 1,000, 2,000,
4,000, 8,000, and 16,000 Hertz (Hz).

35.  Octave band analyzer can be used
to analyze the AC analog output of
the sound level meter.

36. STATISTICAL
ANALYLYZER

37.  The statistical noise analyzer
(SNA) was designed to analyze
very-low-frequency (VLF)/low-frequency
(LF) highly impulsive
atmospheric electromagnetic
noise, which is largely produced
by lightning discharges .

38. Noise Dosimeter
 A noise Dosimeter is a specialized
sound level meter intended
specifically to measure the noise.
 The Dosimeter store the noise level
information and carries out an
averaging process

39.  It measure the
fluctuations in air pressure
caused by sound and
convert into a usable
reading.
 Noise dosimeter is
particularly useful when a
worker moves between
number of location.
 Find out how long the
worker stays at each
location and then
calculate the overall
exposure

40. THANK YOU