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Impacts of Noise

Sound Level Meter

Control of Noise Pollution

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Impacts of Noise

Noise is defined as unwanted sound.

Noise pollution makes men more irritable.

The effect of noise pollution is multifaceted &

inter related.

The impacts of noise on human being, animal

and property are as follows.

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(1) It decreases the efficiency of a man

Regarding the impact of noise on human

efficiency, there are number of experiments

which point out the fact that human efficiency

increases with noise reduction.

Thus human efficiency is related with noise.

Impact of noise on human

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(2) Lack of Concentration

For better quality of work there should beconcentration.

Noise causes lack of concentration.

In big cities, mostly all the offices are on mainroad, the noise of traffic or the loud speakersof different types of horns divert the attentionof the people working in offices.

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(3) Fatigue

Because of noise pollution, people cannot

concentrate on their work.

Thus they have to give their more time for

completing the work and they feel tiring

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(4) Abortion is caused

There should be cool and calm atmosphere

during the pregnancy. Unpleasant sounds make a lady of irritative

nature.

Sudden noise causes abortion in females.

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(5) It causes Blood Pressure

Noise pollution causes certain diseases in

human.

It attacks on the personspeace of mind. Thenoises are recognized as major contributing

factors in accelerating the already existing

tensions of modern living.

The tensions result in certain disease like

blood pressure or mental illness etc.

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(6)Temporary or Permanent Deafness

The effect of noise on audition is wellrecognized in Mechanics, locomotive drivers,telephone operators etc.

All have their hearing impairment as a result ofnoise at the place of work.

Physicist, physicians & psychologists are of

the view that continued exposure to noiselevel above 80 to 100 dB is unsafe.

Loud noise causes temporary or permanentdeafness.

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Impact of Noise on Vegetation

It is well known to all that plants are similar tohuman being.

They are also as sensitive as man.

There should be cool & peaceful environment

for their better growth.

Noise pollution causes poor quality of crops.

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Impact of Noise on Animals

Noise pollution damage the nervous system

of animals.

Animal looses the control of its mind.

They become dangerous.

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Impact of Noise on Property

Loud noise is very dangerous to building,

bridges and monuments.

It creates waves which struck the walls and

put the building in danger condition.

It weakens the edifice of buildings.

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Design

The various elements in a sound level meter are

The transducer; that is, the microphone The electronic amplifier and calibrated

attenuator for gain control

The frequency weighting or analyzing

possibilities The data storage facilities

The display

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Block diagram of a sound level meter

Microphone

Pre

Amplifier

Weighting

networkor filters Amplifier Rectifier AveragingSystem

DisplayAC

Output

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The most important element of sound level

meter is the microphone. The microphone is the interface between the acoustic

field and the measuring system.

It responds to sound pressure and transforms it into

an electric signal which can be interpreted by themeasuring instrument.

The microphone can be of the following types:

(i) Piezoelectric

(ii) Condenser

(iii) Electret

(iv) Dydynamic.

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In a piezoelectric microphone, the membrane isattached to a piezoelectric crystal which generatesan electric current when submitted to mechanicaltension.

The vibrations in the air, resulting from the soundwaves, are picked up by the microphone membraneand the resulting pressure on the piezoelectriccrystal transforms the vibration into an electricsignal.

These microphones are stable, mechanically robustand not appreciably influenced by ambient climaticconditions. They are often used in sound surveymeters.

(i) Piezoelectric Microphone

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In a condenser microphone, the microphone membrane isbuilt parallel to a fixed plate and forms with it a condenser.

A potential differential is applied between the two plates

using a d.c. voltage supply (the polarization voltage). The movements, which the sound waves provoke in the

membrane, given origin to variations in the electricalcapacitance and therefore in a small electric current.

These microphones are more accurate than the other

types and are mostly used in precision sound level meters. However, they are more prone to begin affected by dirt

and moisture.

(ii) Condenser Microphone

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A variation on the condenser microphone which

is currently very popular is the electret.

In this case the potential difference is providedby a permanent electrostatic charge on the

condenser plates and no external polarizing

voltage.

This type of microphone is less sensitive to dirt

and moisture than the condenser microphone.

(iii) Electret Microphone

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(iv) Dynamic Microphone

In dynamic microphone, where the

membrane, is connected to a coil, centered in

a magnetic field, and whose movements,

triggered by the mechanical fluctuations ofthe membrane, give origin to a potential

differential in the poles of the coil.

The dynamic microphone is moremechanically resistant but its poor frequency

response severely limits its use in the field of

acoustics

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Workingof SLM

The electrical signal from the transducer is fed to thepre-amplifier of the sound level mater and aweighted filter over a specified range of frequencies.

Further amplification prepares the signal either foroutput to other instruments such as a tape recorderor for rectification and direct reading on the meter.

The scale on the indicating device is such that thelinear signal may be read in dB. The two maincharacteristic are:

1. Frequency Response

2.Dynamic Range

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(1)The frequency response

This characteristic is, the deviation between

the measured value and true value as a

function of the frequency.

As the ear is capable of hearing sounds

between 20Hz and 20KHz, the frequency

response of the sound level meter should be

good, with variations smaller than 1dB, overthat range.

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Control of Noise Pollution

The techniques employed for noise control

can be broadly classified as

(1) Control at source

(2) Control in the transmission path

(3) Using protective equipment.

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(1)Noise Control at Source

The noise pollution can be controlled at the source of

generation itself by employing following techniques.

(a)Reducing the noise levels from domestic sectors(b) Maintenance of automobiles

(d) Low voice speaking

(c) Control over vibrations

(e) Prohibition on usage of loud speakers

(f) Selection of machinery

(g) Maintenance of machines

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(a) Reducing the noise levels from

domestic sectors

The domestic noise coming from radio,

tape recorders, television sets, mixers,

washing machines, cooking operations

can be minimized by their selective and

judicious operation.

By usage of carpets or any absorbingmaterial, the noise generated from felling

of items in house can be minimized.

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(b) Maintenance of automobiles

Regular servicing and tuning of vehicles will

reduce the noise levels.

Fixing of silencers to automobiles, two

wheelers etc., will reduce the noise levels.

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(c) Control over vibrations

The vibrations of materials may be controlled

using proper foundations, rubber padding

etc., to reduce the noise levels caused by

vibrations.

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(d) Low voice speaking

Speaking at low voices enough for

communication reduces the excess noise

levels.

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(f) Selection of machinery

Optimum selection of machinery tools or

equipment reduces excess noise levels.

For example selection of chairs, or selection

of certain machinery / equipment which

generate less noise (sound) due to itssuperior technology etc. is also an important

factor in noise minimization strategy.

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(g) Maintenance of machines

Proper lubrication and maintenance ofmachines, vehicles etc., will reduce noiselevels.

For example, it is a common experience that,many parts of a vehicle will become loosewhile on a rugged path of journey.

If these loose parts are not properly fitted,they will generate noise and causeannoyance to the driver/passenger.

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(2) Control in the transmission path

The change in the transmission path will increase the

length of travel for the wave and get

absorbed/refracted/radiated in the surrounding

environment.The available techniques are:

(a) Installation of barriers

(b) Installation of panels or enclosures

(c) Green belt development

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(a) Installation of barriers

Installation of barriers between noise source andreceiver can attenuate the noise levels.

The barrier may be either close to the source orreceiver,subjected to the condition that, R

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R D

SourceReceiverBarrier

Barrier close to source

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D

Barrier

Receiver

Source

R

Barrier close to receiver

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(b) Installation of panels or enclosures

A sound source may be enclosed with a paneledstructure such as room as a means of reducing thenoise levels at the receiver.

The actual difference between the sound pressurelevels inside and outside an enclosure depends notonly on the transmission loss of the enclosure

panels but also on the acoustic absorption within theenclosure and the details of the panel penetrationswhich may include windows or doors.

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(c) Green Belt Development

Green belt development can attenuate the

sound levels.

The degree of attenuation varies withspecies of greenbelt.

The statutory regulations direct the

industries to develop greenbelt four timesthe built-up area for attenuation of various

atmospheric pollutants, including noise.

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(3)Using protection equipment

Protective equipment usage is the ultimate step in

noise control technology, i.e. after noise reduction at

source and/or after the diversion or engineered

control of transmission path of noise. The usage of protective equipment and the workers

exposure to the high noise levels can be minimized

by following.

(a) Job rotation

(b) Exposure reduction

(c) Hearing protection

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(a) Job rotation

By rotating the job between the workers workingat a particular noise source , the adverseimpacts can be reduced.

(b) Exposure reduction

The schedule of the workers should be planned in such away that, they should not be over exposed to the high

noise levels.

(c) Hearing protection

Equipment like earmuffs, ear plugs etc. are the commonly used

for hearing protection.Attenuation provided by ear-muffs vary

widely in respect to their size, shape, seal material etc.

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THANK YOU

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