Impacts of Noise

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PH 0101 UNIT 1 LECTURE 9

• 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
Impact of noise on human

• 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.

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(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.

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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 persons 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.

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(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.

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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.

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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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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.
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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
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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 the measuring instrument.
• The microphone can be of the following types
  (i) Piezoelectric
• (ii) Condenser
• (iii) Electret
• (iv) Dydynamic.

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(i) Piezoelectric Microphone

• 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.

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(ii) Condenser 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.

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(iii) Electret 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.

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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 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

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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

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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, over that range.

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(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.

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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
(c) Control over vibrations
(d) Low voice speaking
(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 absorbing material,
  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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(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.

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

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(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.

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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 and
  receiver can attenuate the noise levels.
• The barrier may be either close to the source or
  receiver,subjected to the condition that, Rltlt D
  or in other words, to increase the transverse
  length for the sound wave.

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Barrier
Receiver
Source
D
R
Barrier close to source
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Barrier close to receiver
Barrier
Source
Receiver
D
R
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(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.

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(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.

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

(b) Exposure reduction
The 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.
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