PH 0101 UNIT 1 LECTURE 91 Impacts of Noise Sound Level Meter Control of Noise Pollution.

PH 0101 UNIT 1 LECTURE 9 1

PH 0101 UNIT 1 LECTURE 9

• Impacts of Noise

• Sound Level Meter

• Control of Noise Pollution


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.


(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


(2) Lack of Concentration

• For better quality of work there should be concentration.

• Noise causes lack of concentration.

• In big cities, mostly all the offices are on main road, the noise of traffic or the loud speakers of different types of horns divert the attention of the people working in offices.


(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


(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.


(5) It causes Blood Pressure

• Noise pollution causes certain diseases in human.

• It attacks on the person’s peace of mind. The noises 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.


(6)Temporary or Permanent Deafness

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

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

• Physicist, physicians & psychologists are of the view that continued exposure to noise level above 80 to 100 dB is unsafe.

• Loud noise causes temporary or permanent deafness.


Impact of Noise on Vegetation • It is well known to all that plants are similar to

human 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.


Impact of Noise on Animals

• Noise pollution damage the nervous system of animals.

• Animal looses the control of its mind.

• They become dangerous.


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.


Sound Level Meter

Definition

The instrumentation to determine sound level or noise level is referred as a sound level meter.

Principle The pressure of the sound waves under study actuates the microphone thus converting the acoustical energy into electrical current which in turn serve to operate the display device.


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


Block diagram of a sound level meter

Microphone

Pre Amplifier

Weighting network or filters

Amplifier Rectifier Averaging

System

DisplayAC Output


• 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 the measuring instrument.

• The microphone can be of the following types: (i) Piezoelectric

(ii) Condenser (iii) Electret

(iv) Dydynamic.


• In a piezoelectric microphone, the membrane is attached to a piezoelectric crystal which generates an electric current when submitted to mechanical tension.

• The vibrations in the air, resulting from the sound waves, are picked up by the microphone membrane and the resulting pressure on the piezoelectric crystal transforms the vibration into an electric signal.

• These microphones are stable, mechanically robust and not appreciably influenced by ambient climatic conditions. They are often used in sound survey meters.

(i) Piezoelectric Microphone


• In a condenser microphone, the microphone membrane is built 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 electrical capacitance 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


• A variation on the condenser microphone which is currently very popular is the electret.

• In this case the potential difference is provided by 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


(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 of the membrane, give origin to a potential differential in the poles of the coil.

• The dynamic microphone is more mechanically resistant but its poor frequency response severely limits its use in the field of acoustics


Working of SLM• The electrical signal from the transducer is fed to the

pre-amplifier of the sound level mater and a weighted filter over a specified range of frequencies.

• Further amplification prepares the signal either for output to other instruments such as a tape recorder or for rectification and direct reading on the meter.

• The scale on the indicating device is such that the linear signal may be read in dB. The two main characteristic are:

1. Frequency Response 2.Dynamic Range


(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, over that range.


(2) The dynamic range • This characteristic is, the range in dB over

which the measured value is proportional to the true value, at a given frequency (usually 1000Hz).

• This range is limited at low levels by the electrical background noise of the instrument and at high levels by the signal distortion caused by overloading the microphone or amplifiers.


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.


(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


(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 absorbing material, the noise generated from felling of items in house can be minimized.


(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.


(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.


(d) Low voice speaking

• Speaking at low voices enough for communication reduces the excess noise levels.


(e)Prohibition on usage of loud speakers

• By not permitting the usage of loudspeakers in the habitant zones except for important meetings / functions.

• Now-a-days, the urban administration of the metro cities in India, is becoming stringent on usage of loudspeakers.


(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 its superior technology etc. is also an important factor in noise minimization strategy.


(g) Maintenance of machines

• Proper lubrication and maintenance of machines, vehicles etc., will reduce noise levels.

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

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


(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


(a) Installation of barriers

• Installation of barriers between noise source and receiver can attenuate the noise levels.

• The barrier may be either close to the source or receiver,subjected to the condition that, R<< D or in other words, to increase the transverse length for the sound wave.


R D

SourceReceiverBarrier

Barrier close to source


D

Barrier

Receiver

Source

R

Barrier close to receiver


(b) Installation of panels or enclosures

• A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver.

• The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic absorption within the enclosure and the details of the panel penetrations which may include windows or doors.


(c) Green Belt Development

• Green belt development can attenuate the sound levels.

• The degree of attenuation varies with species of greenbelt.

• The statutory regulations direct the industries to develop greenbelt four times the built-up area for attenuation of various atmospheric pollutants, including noise.


(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 worker’s exposure to the high noise levels can be minimized by following.

(a) Job rotation

(b) Exposure reduction

(c) Hearing protection


(a) Job rotation By rotating the job between the workers working

at a particular noise source , the adverse impacts can be reduced.

(b) Exposure reductionThe schedule of the workers should be planned in such a way 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.


THANK YOU

THANK YOU

PH 0101 UNIT 1 LECTURE 91 Impacts of Noise Sound Level Meter Control of Noise Pollution.

Documents

Transcript of PH 0101 UNIT 1 LECTURE 91 Impacts of Noise Sound Level Meter Control of Noise Pollution.