Post on 19-Jul-2016
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Assoc. Prof. Dr. Amirhossein Malakahmad
Civil Engineering Department
Universiti Teknologi PETRONAS
CO3: To evaluate various sources of air and
noise pollution and propose the relevant
At the end of this session you will be able to:
Justify noise pollution and its importance.
Evaluate noise pollution problems and causes.
Calculate noise level emissions from single and combined sources.
Noise is an environmental pollutant, a waste product generated in conjunction with various
Noise is any sound (independent of loudness) that can produce an undesired physiological or
psychological effect in an individual, and that
may interfere with the social ends of an individual
Noise pollution problems
Noise of sufficient intensity and duration can induce temporary or permanent hearing loss, ranging from
slight harm to nearly total deafness.
In general, a pattern of exposure to any source of sound that produces high enough levels can result in
temporary hearing loss. If the exposure persists over
a period of time, this can lead to permanent hearing
It has been estimated that 1.7 million workers in the United States between 50 and 59 years of age have
enough hearing loss to be awarded compensation.
Why noise pollution is taken for granted?
Noise, if defined as unwanted sound, is a subjective experience. What is considered noise by one listener may be considered desirable by another.
Noise has a short decay time and thus does not remain in the environment for extended periods, as do air and water pollution.
To those persons whose hearing may already have been affected by noise, it may not be considered a problem at all.
Noise level calculations
Example 1 - Calculate the difference in
dB If the second produces:
a. twice as much power than the first,
b. 10 times the power of the first,
c. A million times the power of the
A scale based on the logarithm of the ratios of the measured quantities is used to calculate the noise. The unit for these types of measurement scales is the decibels (dB).
L = level, decibels (dB)
Q = measured quantity
Q0= reference quantity
log = logarithm in base 10
Combining sound pressure levels
When sound pressure levels are combined the total level cannot be predicted by simply adding
In terms of the basics, we need to work out the power that each level represents, add those
powers together and turn the total back into a
Example 2 - What sound
power level results from
combining the following
three levels: 68 dB, 79dB,
and 75 dB?
Example 3 - A motorcyclist is warming up his racing
cycle at a racetrack approximately 200 m from a
sound level meter. The meter reading is 56 dB. What
meter reading would you expect if 15 of the
motorcyclist's competitors join him whit motorcycles
having the same sound emission characteristics?
Conduct your calculations via both sound level
differences and sound combinations methods.