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PH 0101 UNIT 1 LECTURE 9

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.

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PH 0101 UNIT 1 LECTURE 9

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  1. PH 0101 UNIT 1 LECTURE 9 • Impacts of Noise • Sound Level Meter • Control of Noise Pollution PH 0101 UNIT 1 LECTURE 9

  2. 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. PH 0101 UNIT 1 LECTURE 9

  3. (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. PH 0101 UNIT 1 LECTURE 9

  4. (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. PH 0101 UNIT 1 LECTURE 9

  5. (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 PH 0101 UNIT 1 LECTURE 9

  6. (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. PH 0101 UNIT 1 LECTURE 9

  7. (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. PH 0101 UNIT 1 LECTURE 9

  8. (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. PH 0101 UNIT 1 LECTURE 9

  9. 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. PH 0101 UNIT 1 LECTURE 9

  10. Impact of Noise on Animals • Noise pollution damage the nervous system of animals. • Animal looses the control of its mind. • They become dangerous. PH 0101 UNIT 1 LECTURE 9

  11. 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. PH 0101 UNIT 1 LECTURE 9

  12. 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. PH 0101 UNIT 1 LECTURE 9

  13. 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 PH 0101 UNIT 1 LECTURE 9

  14. Pre Amplifier Weighting network or filters Amplifier Rectifier Averaging System Microphone Display AC Output Block diagram of a sound level meter PH 0101 UNIT 1 LECTURE 9

  15. 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. PH 0101 UNIT 1 LECTURE 9

  16. (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. PH 0101 UNIT 1 LECTURE 9

  17. (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. PH 0101 UNIT 1 LECTURE 9

  18. (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. PH 0101 UNIT 1 LECTURE 9

  19. (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 PH 0101 UNIT 1 LECTURE 9

  20. Workingof 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 PH 0101 UNIT 1 LECTURE 9

  21. (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. PH 0101 UNIT 1 LECTURE 9

  22. (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. PH 0101 UNIT 1 LECTURE 9

  23. 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. PH 0101 UNIT 1 LECTURE 9

  24. (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 PH 0101 UNIT 1 LECTURE 9

  25. (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. PH 0101 UNIT 1 LECTURE 9

  26. (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. PH 0101 UNIT 1 LECTURE 9

  27. (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. PH 0101 UNIT 1 LECTURE 9

  28. (d) Low voice speaking • Speaking at low voices enough for communication reduces the excess noise levels. PH 0101 UNIT 1 LECTURE 9

  29. (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. PH 0101 UNIT 1 LECTURE 9

  30. (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. PH 0101 UNIT 1 LECTURE 9

  31. (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. PH 0101 UNIT 1 LECTURE 9

  32. (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 PH 0101 UNIT 1 LECTURE 9

  33. (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. PH 0101 UNIT 1 LECTURE 9

  34. Barrier Receiver Source D R Barrier close to source PH 0101 UNIT 1 LECTURE 9

  35. Barrier close to receiver Barrier Source Receiver D R PH 0101 UNIT 1 LECTURE 9

  36. (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. PH 0101 UNIT 1 LECTURE 9

  37. (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. PH 0101 UNIT 1 LECTURE 9

  38. (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 PH 0101 UNIT 1 LECTURE 9

  39. (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. PH 0101 UNIT 1 LECTURE 9

  40. THANK YOU THANK YOU PH 0101 UNIT 1 LECTURE 9

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