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Q What is a decibel? I have read that N
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(number of decibels)=10 log I,/12 where I, = the intensity of a given sound in Watts and 12= the intensity of the loudest sound the human ear can just not detect. Can you explain the meaning of this equation in terms of the noise produced by a typical vehicle engine? If the sound intensity is doubled, is the number of decibels also doubled?
A The decibel scale of loudness starts at
the "threshold of audition", that is the loudest sound that the human ear can just not detect. Referring to the normal noise range of automotive engines and assuming that 100dB = 1 unit of intensity, 90dB =4unit, 80dB unit and 70dB =i unit. Thus a reduction in loudness of 10dB equals the reduction intensity of 50 per cent. An engine producing 80dB will therefore operate with a loudness intensity of a quarter of that produced by a 100dB engine.