Physics For Civil Engineering: Unit III: Acoustics and Lighting Designs
Noise Measurement
Sound (Noise) Level, Noise meters
Sound and unwanted sound, called noise, is the result of fluctuations or oscillations in atmospheric pressure. These excite the ear mechanism and evoke the sensation of hearing.
NOISE MEASUREMENT
Sound
(Noise) Level
Sound
and unwanted sound, called noise, is the result of fluctuations or oscillations
in atmospheric pressure. These excite the ear mechanism and evoke the sensation
of hearing.
The human ear responds to changes in
sound pressure over a very wide range - the loudest sound pressure to which the
human ear responds is ten million times greater than the softest. This large
ratio is reduced to a more manageable size by the use of logarithms.
The
logarithms scale provides a more convenient way of comparing the sound pressure
of one sound with another. To avoid a scale which is too compressed, a factor
of 10 is ving rise to introduced, giving the decibel unit.
It
is a ratio, expressed in logarithmic scale relative to a reference sound
pressure level.
1
decibel (dB) 10 log10 (intensity measured / reference intensity)
The reference intensity used in the
threshold of hearing which means sound which can be first heard at the sound
pressure of 2 x 10-5 Newtons per sq. meter or sound intensity
of
10-12watts per sq. meter.
The
level of sound pressure p is said to be Lp decibels greater
than a reference sound pressure Pref according to the following definition:
where P is the sound pressure
fluctuation (above or below atmospheric pressure) and Pref is 20
micropascals (2 x 10-5 Pa), which is approximately the threshold of
hearing.
Noise
meters
These are the instruments specially
designed for noise measurement from low to high frequencies, characteristics of
human ear capacity. Noise meters record the dB scale for routine measurement of
general noise levels.
Refined
noise meters have been developed to take care of peak noise levels, duration of
noise exposure and quality of noise which are aspects of specified noise
situation.
Decibel scale is shown in figure 3.4
TABLE
3.3
Sound
Measurement (Intensities, Pressures and Decibels) in Air at Room Temperature
and Sea Level Pressure
Physics For Civil Engineering: Unit III: Acoustics and Lighting Designs : Tag: : Sound (Noise) Level, Noise meters - Noise Measurement
Physics For Civil Engineering: Unit III: Acoustics and Lighting Designs
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Physics for Civil Engineering
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