Noise Pollution Noise & Our Hearing Level of Noise Measurement of Noise Classification of Noise Sources of noise Impacts of noise Control of noise pollution Conclusion

Noise is unwanted sound. Sound is a form of energy

which is emitted by a vibrating body and on reaching the ear causes the sensation of hearing through nerves. Or we can say when the effects of sound are undesirable it termed as NOISE

The inner ear of humans contains a snail-shaped structure called a cochlea that is lined with thousands of microscopic hairs. When sound vibrations enter the cochlea, they cause the tiny hairs to move back and forth. If strong vibrations blast into the cochlea, the hairs can be flattened and damaged.

Sound is the quickly varying pressure wave travelling through a medium. When sound travels through air, the atmospheric pressure varies periodically. The number of pressure variations per second is called the frequency of sound.

The response of the human ear to sound is dependent on the frequency of the sound. The human ear has peak response around 2,500 to 3,000 Hz and has a relatively low response at low frequencies.

To express sound or noise in terms of Pa is quite inconvenient because we have to deal with numbers from as small as 20 to as big as 2,000,000,000. A simpler way is to use a logarithmic scale. As such, the loudness of sound is commonly expressed in decibel (dB).

Sound Levels and Human Response Common sounds Noise Level [dB] Effect

Rocket launching pad, (no ear protection) 180 Irreversible hearing loss

Carrier deck jet operation, Air raid siren 140 Painfully loud Thunderclap 130

Jet takeoff (200 ft), Auto horn (3 ft) 120 Maximum vocal effort

Pile driver, Rock concert 110 Extremely loud

Garbage truck, Firecrackers 100 Very loud

Heavy truck (50 ft), City traffic 90 Very annoying

Hearing damage (8 Hrs) Alarm clock (2 ft), Hair dryer 80 Annoying

Noisy restaurant, Freeway traffic, Business office

70 Telephone use difficult

Air conditioning unit Conversational speech

60 Intrusive

Light auto traffic (100 ft) 50 Quiet Living room, Bedroom, Quiet office 40

Library, Soft whisper (15 ft) 30 Very quiet Broadcasting studio 20

10 Just audible 0 Hearing begins

Sound Power Sound Intensity

Sound Pressure

If a sound source has a pressure of 2000µPa at 10m distance, compute:

a) The sound pressure level in dB,

b) The sound intensity in W/m2, c) The sound power in W.

a) Lp = 40dB b) I = 9.9x10-9 W/m2

c) W = 12.5x10-6 W

1) Community Noise/Environmental Noise

2) Occupational Noise a) Continuous Noise b) Intermittent Noise c) Impulsive Noise

It is also known as, Environmental Noise Domestic Noise Residential Noise Sources: Road, Rail, Air traffic Construction and Public works Restaurant, cafeteria etc. Sporting events like motor sports Play grounds Parks

Sources: Industrial Machinery

includes, Rotors, gears, electrical

machines. Combustion engines Drilling, crushing Pneumatic equipment

Occupational

Noise

Continuous

Noise

Impulsive Noise

Intermittent

Noise

It is produced by the machinery that operates without interruption e.g.

Pumps, Compressors and Processing equipments