background image NOAAVents ProgramAcoustics Program
  Monitoring the global ocean through underwater acoustics
non-clickable go to Acoustics home non-clickable scroll down for Methods non-clickable scroll down for Results non-clickable scroll down for Multimedia non-clickable
non-clickable non-clickable non-clickable non-clickable
  Underwater Acoustics Tutorial- 2. The Decibel Scale  
  2. The Decibel Scale  

common sounds

dB SPL in air

threshold of hearing 0 dB
whisper at 1 meter 20 dB
normal conversation 60 dB
jet engine 140 dB
painful to human 130 dB
Warning: noise levels cited in air do not equal underwater levels for reasons that will be described in the following sections.

If the amplitude of a sound is increased in a series of equal steps, the loudness of the sound will increase in steps which are perceived as successively smaller. Because sound "loudness" varies exponentially, we'd normally have to deal with a lot of zeros when doing computations involving the parameters of sound, and we'd have to multiply numbers rather than simply add and subtract them. Therefore, sound intensity is usually measured with the decibel scale in which the steps are not equal, but get progressively louder. By using the decibel scale, calculations are simplified and relative values relate more closely to perception. A pressure in decibels expresses a ratio between the measured pressure and a reference pressure (see SPL and SIL). On the decibel scale, everything refers to power, which is amplitude squared.; 0.0 dB corresponds to about the normal threshold of hearing and 130 dB to the point where sound becomes painful to humans.


  Previous | Next  
Vents Home Contacts-Credits Bibliography Links Disclaimer Privacy Policy