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Acoustics and Noise Control

Acoustics and Noise Control

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Acoustics and Noise Control

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  1. Acoustics and Noise Control Lecturer: SachinJasuja

  2. Previous Lecture • Sound Propagation • Speed of Sound • Sound Intensity • Measurement (Decibel)

  3. Learning Outcomes At the end of this topic, you should be able to: • PSYCHO-ACOUSTICS • Threshold hearing • Loudness • Pitch • Masking • Types of noise

  4. Acoustics • Acoustics: the science concerned with the production, control, transmission, reception, and effects of sound. The term is derived from the Greek akoustos, meaning “hearing.” • Many people mistakenly think that acoustics is strictly musical or architectural in nature. While acoustics does include the study of musical instruments and architectural spaces, it also covers a vast range of topics, including: noise control, SONAR for submarine navigation, ultrasounds for medical imaging, seismology, and electroacoustic communication etc.

  5. PSYCHO-ACOUSTICS • Given sufficient sound pressure level, a healthy, young, normal human ear is able to detect sounds with frequencies from 20 Hz to 20,000 Hz. • Sound characterisedby frequencies between 1 and 20 Hz is called infrasound and is not considered damaging at levels below 120 dB. Sound characterised by frequencies in excess of 20,000 Hz is called ultrasound and is not considered damaging at levels below 105 dB. Sound which is most damaging to the range of hearing necessary to understand speech is between 500 Hz and 2000 Hz.

  6. Threshold of hearing • The threshold of hearing is defined as the level of a sound at which, under specified conditions, a person gives 50% correct detection responses on repeated trials. • The threshold of hearing is at an intensity of I0 = 10-12 W/m2 (lowest intensity which can be heard under ideal conditions by a person with excellent hearing).

  7. Loudness • At the threshold of hearing, a noise is just "loud" enough to be detected by the human ear. Above that threshold, the degree of loudness is a subjective interpretation of sound pressure level or intensity of the sound. • The human ear has different sensitivities to different frequencies, being least sensitive to extremely high and extremely low frequencies. • E.g., a pure-tone of 1000 Hz with intensity level of 40 dB would impress the human ear as being louder than a pure-tone of 80 Hz with 50 dB, and a 1000 Hz tone at 70 dB would give the same subjective impression of loudness as a 50 Hz tone at 85 dB.

  8. Pitch • Pitch is the subjective response to frequency. • Low frequencies are identified as "low-pitched", • High frequencies are identified as "high-pitched". • In a complex note, lowest frequency sound determines the pitch of the sound.

  9. Masking • Masking is the phenomenon of one sound interfering with the perception of another sound. For example, the interference of traffic noise with the use of a public telephone on a busy street corner is probably well known to everyone. • Masking is a very important phenomenon and it has two important implications: • speech interference, by which communications can be impaired because of high levels of ambient noise; • utilisation of masking as a control of annoying low level noise, which can be "covered" by music for example. • It has been shown that low frequency sounds can effectively "mask" high frequency sounds even if they are of a slightly lower level.

  10. Frequency Weighting • Human ear is not equally sensitive to sound at different frequencies. To adequately evaluate human exposure to noise, the sound measuring system must account for this difference in sensitivities over the audible range. For this purpose, frequency weighting networks, which are really "frequency weighting filters" have been developed. These networks "weight" the contributions of the different frequencies to the over-all sound level, so that sound pressure levels are reduced or increased as a function of frequency before being combined together to give an overall level. The two internationally standardised weighting networks in common use are the "A" and "C", which have been built to correlate to the frequency response of the human ear for different sound levels.

  11. Frequency Weighting • “A” Network is a useful simple means of describing interior noise environments from the point of view of habitability, community disturbance, and also hearing damage, • While “C” network better describes the loudness of industrial noise which contributes significantly to hearing damage. Its great attraction lies in its direct use in measures of total noise exposure

  12. Types of Noise Noise may be classified as steady, non-steady or impulsive, depending upon the temporal variations in sound pressure level. • Steady noise: is a noise with negligibly small fluctuations of sound pressure level within the period of observation. • Non- Steady noise: A noise is called non-steady when its sound pressure levels shift significantly during the period of observation. This type of noise can be divided into intermittent noise and fluctuating noise.

  13. Types of Noise • Fluctuating noise:is a noise for which the level changes continuously and to a great extent during the period of observation. • Intermittent noise:is noise for which the level drops to the level of the background noise several times during the period of observation. The time during which the level remains at a constant value different from that of the ambient background noise must be one second or more.

  14. Types of Noise • Impulsive noise consists of one or more bursts of sound energy, each of a duration less than about 1s . Impulses are usually classified as type A and type B as described in Figure. • Type A characterisestypically gun shot types of impulses, while type B is the one most often found in industry (e.g., punch press impulses).

  15. Recap • PSYCHO-ACOUSTICS • Threshold hearing • Loudness • Pitch • Masking • Types of noise

  16. Questions and Answers Q and A?

  17. Thank You!

  18. Acoustics and Noise Control Lecturer: SachinJasuja

  19. Next Lecture • Noise Control

  20. Previous Lecture • PSYCHO-ACOUSTICS • Threshold hearing • Loudness • Pitch • Masking • Types of noise

  21. Learning Outcomes At the end of this topic, you should be able to: • Noise Control

  22. Noise Control • Administrative Control • Engineering Control • Personal Protective Equipment ( hearing protective devices)

  23. Administrative Controls • Operate noisy equipment on second or third shifts. • Rotate employees through high-noise areas. • Modify existing machinery. • Place noise limit specs. on new equip. • Maintain equip. in good condition. • Use noise control when installed. • Reporting noisy equip. to supervisor for repair.

  24. Engineering Controls • Reduce noise at the source. • Interrupt the noise path. • Reduce reverberation and structural vibration.

  25. Personal Protective Equipment (Hearing Protection Devices - HPD) • Employers shall provide to employees exposed to 8 hrTWA (time Weighted Average) of 85 dB at no cost. • Employers shall ensure being worn: • by employees exposed to 8 hrTWA of 90dB or greater • by employees exposed to 8 hrTWA of 85dB or greater and: • Whose baseline audiogram has not been established • Who have experienced a threshold shift

  26. Hearing Protection Device (HPD)Noise Reduction • HPD must reduce employee noise exposure below PEL (Permissible Exposure Level) e.g. below 8 hrTWA of 90 dB. • Employees with standard threshold shift (STS), HPD must reduce employees noise exposure below an 8 hr TWA of 85 dB.

  27. Hearing Protection Use • Voluntary Use • Exposed to an 8 hr TWA of 85 dB • Mandatory Use • Exposed to an 8 hr TWA of 90 dB • Exposed to an 8 hr TWA of 85 dB but have not had a baseline hearing test • Employees who have suffered STS hearing loss and are exposed to an 8 hr TWA of 85 dB

  28. Employee Responsibility • Understand the need for hearing protection devices. • Wear HPDs and seek replacements. • Encourage co-workers to wear HPDs. • Communicate problems to supervisors.

  29. Management Responsibility • Provide occupational noise training. • Provide hearing protection devices. • Demonstrate commitment – wear HPDs. • Enforce the use of HPDs. • Keep up to date with HPD selection and use. • Encourage questions and resolve problems.

  30. Purpose of Hearing Protectors • Reduction of sound waves traveling to the inner ear

  31. Advantages and Disadvantages of Different Types of Hearing Protectors

  32. Attenuation of Different Types of Hearing Protectors • Ear Plugs • Reduce noise by as much as 30 decibels • Ear Canals • Reduce noise by as much as 30 decibels • Used when individual is unable to use traditional ear plugs • Ear Muffs • Reduce noise by as much as 15-30 decibels • Use in conjunction with ear plugs when exposed to high noise levels (105+ decibels)

  33. Instructions on Selection, Fitting, Use, and Care of Hearing Protectors Ear plugs • Keep clean and free of materials • Wash in mild liquid detergent and warm water • Squeeze excess water and air dry • Discard plugs when hardened or do not re-expand • Ear Canals • Clean like normal ear plugs • Do not tamper with the headband and the acoustic seal

  34. Instructions on Selection, Fitting, Use, and Care of Hearing Protectors • Ear Muffs • Keep clean and free of debris • Clean cushions with warm soapy water • Do not tamper with the acoustic seal between the cushions and the headband • Do not modify the ear muffs in any way • Do not stretch or abuse the headband

  35. Recap • Noise Control • Administrative Control • Engineering Control • Personal Protective Equipment ( hearing protective devices)

  36. Questions and Answers Q and A?

  37. Thank You!

  38. Next Lecture • Effects of Noise • On Human Being • On Animals • On Vegetation • On Property • Mitigation of Noise

  39. Acoustics and Noise Control Lecturer: SachinJasuja

  40. Previous Lecture • Noise Contol • Administrative Control • Engineering Control • Personal Protective Equipment ( hearing protective devices)

  41. Learning Outcomes At the end of this topic, you should be able to: • Effects of Noise • On Human Being • On Animals • On Vegetation • On Property • Mitigation of Noise

  42. Problems of Noise PollutionNoise pollution makes men more irritable. The effect of noise pollution is multifaceted & inter related. The effects of Noise Pollution on Human Being, Animal and property are as follows: • Hearing Impairment • It Decreases the Efficiency of A Man • Lack of concentration • Abortion is caused • Pupil Dilation • Mental Illness • It Causes Heart Attack • Digestive problems • Temporary or permanent Deafness • Aggressive Behavior • Effect on Vegetation Poor Quality of Crops • Effect on Animal • Effect on Property • Sleep interference • Speech interference

  43. HEARING IMPAIRMENT Hearing is essential for well-being and safety. Hearing impairment is typically defined as an increase in the threshold of hearing as clinically assessed by audiometry. There is general agreement that exposure to sound levels less than 70 dB does not produce hearing damage, regardless of the duration of exposure. There is also general agreement that exposure for more than 8 hours to sound levels in excess of 85 dB is potentially hazardous; to place this in context, 85 dB is roughly equivalent to the noise of heavy truck traffic on a busy road

  44. The WHO recommends that unprotected exposure to sound levels greater than 100 dB (for example, the sound of a jackhammer or a snowmobile) should be limited in duration (4 h) and frequency (four times/yr).The threshold for pain is usually given as 140 dB, a level readily achieved in today's boom-cars. Impulse noise exposure (gunfire and similar sources of intense noise of brief duration) should never exceed 140 dB in adults and 120 dB in children. Firecrackers, cap pistols, and other toys can generate sufficient sound levels to cause sudden and permanent hearing loss. Levels greater than 165 dB, even for a few milliseconds, are likely to cause acute cochlear damage. It is important to remember to counsel patients that ears do not get used to loud noise. As the League for the Hard of Hearing notes-they get deaf.

  45. IT DECREASES THE EFFICIENCY OF A MAN Regarding the impact of noise on human efficiency there are number of experiments which print out the fact that human efficiency increases with noise reduction. A study by Sinha & Sinha in India suggested that reducing industrial booths could improve the quality of their work. Thus human efficiency is related with noise. Noise can adversely affect performance, for example in reading, attentiveness, problem solving and memory.

  46. 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. Deficits in concentration can lead to accidents.

  47. 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 ABORTION There should be cool and calm atmosphere during the pregnancy. Unpleasant sounds make a lady of irriative nature. Sudden Noise causes abortion in females. PUPIL DILATION Noise Pollution causes dilation of the pupil of the eye

  48. IT CAUSES MENTAL ILLNESS • 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. These tensions result in certain disease like blood pressure or mental illness etc.. • Noise pollution may cause or contribute to the following adverse effects: anxiety, stress, nervousness, nausea, headache, emotional instability, argumentativeness, sexual impotence, changes in mood, increase in social conflicts, neurosis, hysteria, and psychosis.

  49. It Causes Heart Attack Noise Pollution causes Increase in the rate of heart-beat, increased cholesterol level and Constriction of blood vessels which leads to blood pressure that resulted in heart attack. Noise can trigger both endocrine and autonomic nervous system responses that affect the cardiovascular system and thus may be a risk factor for cardiovascular. High levels of stress hormones such as cortisol, adrenaline, and noradrenalin can lead to hypertension, stroke, heart failure, and immune problems. Acute exposure to noise activates nervous and hormonal responses, leading to temporary increases in blood pressure, heart rate, and vasoconstriction.

  50. Digestive Problems Noise Pollution causes digestive spasms and stomach disorders Temporary or Permanent Deafness The effect of noise on audition is well recognized. 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. Aggressive Behavior Noise above 80 dB may increase aggressive behavior. Annoyance is defined as a feeling of displeasure associated with any agent or condition believed by an individual to adversely affect him or her.