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  1. Def: Unwanted sound, Wrong sound in wrong place at the wrong time
  2. Properties:
    1. Loudness: intensity depends upon the amplitude of vibrations which initiated the noise; a daily exposure of 85 dB is the limit people can tolerate without damage to hearing; measured by Sound level meter.
    2. Frequency: denoted as Hertz or Hz; human ear can hear frequencies b/w 20 – 20000 Hz; measured by Octave band frequency analyzer.
    3. Audiometer is used to measure the hearing ability. Zero line at the top in the audiogram represents normal hearing; noise induced hearing loss shows a characteristic dip in the curve at the 4000 Hz frequency.
  3. Acceptable levels
    1. Educational Class room; 30-40 db
    2. Library – 35-45 db
    3. Office – 35-45
    4. Conference-40-45
    5. Industrial workshop-40-60
    6. Hospital-20-35
  4. Remember
    1. Upper limit of tolerance of noise is less than 90 decibels
    2. At 160 db there is rupture of tympanic membrane
    3. Repeated exposure of 100 db there is permanent damage to the hearing ability.
    4. Recommended maximum is 85 Db
  5. Sound levels of some noise

Sound of noise

Sound level (dB)



Speech 2-3 people


Speech on radio


Children shouting


Children crying


Music on radio


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