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NOISE
MEASUREMENT
& ABATEMENT
Dr. Papu Kumar Naik
The nature of sound
Sound, a manifestation of vibration, travels in wave patterns through
solids, liquids and gases.
The waves, caused by vibration of the molecules, follow sine functions,
typified by the amplitude and wavelength (or frequency)
Sound waves of equal
amplitude with increasing
frequency from top to
bottom
Sound propagation
Amplitude and wavelength
(period)
Sound pressure for known sounds
How sound is measured
•Pressure, P, usually Pascals
•Frequency, f, usually Hertz
•Intensity, I, usually W/m2
•Bels, L’, derived from logarithmic ratio
•Decibels, L, derived from bels
P = 1/f
I = W/A
L’ = log (Q/Qo)
L = 10*log (Q/Qo)
E.g. Implications of the decibel scale: doubling sound level
would mean that the sound will increase by 10*log2 = +3dB
Ten times the sound level = 10*log10 = +10dB
Exposure to high sound levels
Reflecting on noise
 “Noise" derived from "nausea," meaning seasickness
 Noise is among the most pervasive pollutants today
 Noise is unavoidable for many machines
 We experience noise in a number of ways
environmental
cause and victim
generated by others “second-hand”
 Noise negatively affects human health and well-being
 The air into which second-hand noise is emitted and
on which it travels is a "commons“, a public good
Chart method – adding decibels
Chart method – subtracting background noise
Sound and human hearing
People generally hear sounds
between the “threshold of hearing”
and the “threshold of pain”
In terms of pressure,
this is 20 μPa – 100 Pa
The decibel scale was developed from this fact
and makes numbers more manageable
The decibel scale generally ranges from
approximately 0 to 130
How Sound is Heard
Human hearing and Frequency
0 16 Hz 20 kHz 5 MHz
Sound and human hearing – Frequency
Humans are less sensitive to low frequency
sound and more sensitive to high frequency
sound. Therefore, sometimes the dB scale is
adjusted to take this into account:
A-weighting (db(A)): adjusts overall scale so it
better matches what the human ear would hear
C-weighting (dB(C)): adjusts scale for loud or
low frequency sounds
B-weighting (dB(B)): adjusts by factors that are
“in between” the A-weighted factors and C-
weighted factors (rarely used)
Loudness in phons
The phon is related to dB by the psychophysically measured
frequency response. Phons = dB at 1 kHz. For other frequencies,
the phon scale is determined by loudness experience by humans.
Loudness in sones
The sone is derived from psychophysical tests where
humans judge sounds to be twice as loud. This relates
perceived loudness to phons. A sone is 40 phons. A
10 dB increase in sound level corresponds to a perceived
doubling of loudness. So that approximation is used in the
definition of the phon: 0.5 sone = 30 phon, 1 sone =
40 phon, 2 sone = 50 phon, 4 sone = 60 phon, etc.
Other descriptors of sound
Equivalent sound level – the level of sound that has
the same acoustical energy as does a time-varying
sound over a stated time period.
Percentile sound level – the sound level exceeded “n”
percent of the observation time interval.
Day-night average sound level – the equivalent sound
level for a 24-h period that incorporates a decibel
penalty during night hours.
Major transportation sources of
noise pollution: rail, road, and air
Roadway Noise - Solutions
• Regulations limit the amount of noise
some vehicles can produce
• Some regulations require vehicles to be
properly operated and maintained
• Despite regulations, the noise levels are
usually only reduced by 5 to 10 dBA
Roadway Noise - Solutions
Barriers
•Buffer zones
•Earth berms/wooden fences/concrete walls
•Vegetation (if dense enough)
Aesthetic noise barrier
Roadway Noise - Solutions
Pavement type
Certain asphalts, such as those containing
rubber or stone, can be less noisy than other
pavements.
However, some studies have shown the
reduction in noise is only a few decibels, not
enough to be significant.
More research is needed before pavement
type can be an effective noise-reducing
technique
Noise contours around
an airport calculated
using INM (Integrated
Noise Modeling) based
on previous noise
measurements
55 - 60 dB = Light blue
60 - 70 dB = Dark blue
70 - 75 dB = Red
75 - 80 dB = Green
80 - 85 dB = Yellow
> 85 dB = Pink
Airport Noise
Other sources of noise pollution that
need to be addressed
• Boat noise,
especially jet skis
• Construction noise
• Industry

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Noise pollution_2.ppt

  • 2. The nature of sound Sound, a manifestation of vibration, travels in wave patterns through solids, liquids and gases. The waves, caused by vibration of the molecules, follow sine functions, typified by the amplitude and wavelength (or frequency) Sound waves of equal amplitude with increasing frequency from top to bottom
  • 5. Sound pressure for known sounds
  • 6. How sound is measured •Pressure, P, usually Pascals •Frequency, f, usually Hertz •Intensity, I, usually W/m2 •Bels, L’, derived from logarithmic ratio •Decibels, L, derived from bels P = 1/f I = W/A L’ = log (Q/Qo) L = 10*log (Q/Qo) E.g. Implications of the decibel scale: doubling sound level would mean that the sound will increase by 10*log2 = +3dB Ten times the sound level = 10*log10 = +10dB
  • 7. Exposure to high sound levels
  • 8. Reflecting on noise  “Noise" derived from "nausea," meaning seasickness  Noise is among the most pervasive pollutants today  Noise is unavoidable for many machines  We experience noise in a number of ways environmental cause and victim generated by others “second-hand”  Noise negatively affects human health and well-being  The air into which second-hand noise is emitted and on which it travels is a "commons“, a public good
  • 9. Chart method – adding decibels
  • 10. Chart method – subtracting background noise
  • 11. Sound and human hearing People generally hear sounds between the “threshold of hearing” and the “threshold of pain” In terms of pressure, this is 20 μPa – 100 Pa The decibel scale was developed from this fact and makes numbers more manageable The decibel scale generally ranges from approximately 0 to 130
  • 12. How Sound is Heard
  • 13. Human hearing and Frequency 0 16 Hz 20 kHz 5 MHz
  • 14. Sound and human hearing – Frequency Humans are less sensitive to low frequency sound and more sensitive to high frequency sound. Therefore, sometimes the dB scale is adjusted to take this into account: A-weighting (db(A)): adjusts overall scale so it better matches what the human ear would hear C-weighting (dB(C)): adjusts scale for loud or low frequency sounds B-weighting (dB(B)): adjusts by factors that are “in between” the A-weighted factors and C- weighted factors (rarely used)
  • 15. Loudness in phons The phon is related to dB by the psychophysically measured frequency response. Phons = dB at 1 kHz. For other frequencies, the phon scale is determined by loudness experience by humans.
  • 16. Loudness in sones The sone is derived from psychophysical tests where humans judge sounds to be twice as loud. This relates perceived loudness to phons. A sone is 40 phons. A 10 dB increase in sound level corresponds to a perceived doubling of loudness. So that approximation is used in the definition of the phon: 0.5 sone = 30 phon, 1 sone = 40 phon, 2 sone = 50 phon, 4 sone = 60 phon, etc.
  • 17. Other descriptors of sound Equivalent sound level – the level of sound that has the same acoustical energy as does a time-varying sound over a stated time period. Percentile sound level – the sound level exceeded “n” percent of the observation time interval. Day-night average sound level – the equivalent sound level for a 24-h period that incorporates a decibel penalty during night hours.
  • 18.
  • 19. Major transportation sources of noise pollution: rail, road, and air
  • 20. Roadway Noise - Solutions • Regulations limit the amount of noise some vehicles can produce • Some regulations require vehicles to be properly operated and maintained • Despite regulations, the noise levels are usually only reduced by 5 to 10 dBA
  • 21. Roadway Noise - Solutions Barriers •Buffer zones •Earth berms/wooden fences/concrete walls •Vegetation (if dense enough)
  • 23. Roadway Noise - Solutions Pavement type Certain asphalts, such as those containing rubber or stone, can be less noisy than other pavements. However, some studies have shown the reduction in noise is only a few decibels, not enough to be significant. More research is needed before pavement type can be an effective noise-reducing technique
  • 24. Noise contours around an airport calculated using INM (Integrated Noise Modeling) based on previous noise measurements 55 - 60 dB = Light blue 60 - 70 dB = Dark blue 70 - 75 dB = Red 75 - 80 dB = Green 80 - 85 dB = Yellow > 85 dB = Pink Airport Noise
  • 25. Other sources of noise pollution that need to be addressed • Boat noise, especially jet skis • Construction noise • Industry