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Consider the following statements related to noise: 1. The range of sound power and sound pressures produced is from 0.0002 μ bars to 2000 μ bars. 2. Human ears do not respond linearly to increase in sound pressures. 3. Regular exposure to moderate noise makes the human ear more resistant to occasional exposures of high-intensity noise. Which of the above statements are correct?

Consider the following statements related to noise: 1. The range of sound power and sound pressures produced is from 0.0002 μ bars to 2000 μ bars. 2. Human ears do not respond linearly to increase in sound pressures. 3. Regular exposure to moderate noise makes the human ear more resistant to occasional exposures of high-intensity noise. Which of the above statements are correct? Correct Answer 1 and 2 only

Concept:

Sound pressure (or acoustic pressure):

  • It is the local pressure deviation from the ambient atmospheric pressure, caused by a sound wave. In simpler terms, sound pressure is the amount of air pressure fluctuation a noise source creates The SI unit of sound pressure is the pascal (Pa).
  • The sound pressure of the faintest sound that can be heard by a normal healthy individual is about 20 µPa whereas the loudest astronomical sound pressure may be about 200 Pa (Example: Sound pressure at lift off stage of a Saturn rocket). So, the sound pressure range is 20 µPa to 200 Pa.
  • Now, as 1 Pa = 10-5 Bar, so the sound pressure range is 0.0002 µbar to 2000 µbar.

 

Sound power: It is the sound energy transferred per second from the noise source to the air. Sound power is expressed in watts (W). For example, a human breath generates a sound power of 10-11 watts, a truck horn 0.1 W, and a turbo jet engine 100,000 W.

Hearing range (or audible range): It is a description of the range of the pitches and loudness levels of sound a person can hear before feeling discomfort. For a person with normal hearing, hearing range starts low at about 20 Hz and the highest possible frequency heard without discomfort is 20,000Hz. But human ears do not respond linearly to the increasing sound in this range instead responds logarithmically.

Regular exposure to moderate noise does not make the human ear more resistant to occasional exposures of high-intensity noise. Whether or not human ear is exposed to moderate noise regularly, high intensity noise will introduce noise induced hearing loss. A high intensity sound can make temporary as well as permanent hearing changes.

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