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

control principles.

Unit objectives

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 – Definition

Noise is an environmental pollutant, a waste

product generated in conjunction with various

anthropogenic activities.

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

or group.

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

damage.

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

first.

Measuring scale

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

the levels.

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

decibel figure.

etcL

LLL

total101010

321

101010log10

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.