Measurement of sound

In order to measure sound levels, a “sound level meter” is used, which transforms the acoustic energy into electrical voltage. If sound sources are doubled, this amounts to increasing the intensity by 3 dB. In contrast, the “sensation” of doubling of the intensity only occurs with an increase of 10 dB. However, acoustics does not content itself with “physically” measuring sounds; indeed as we have seen, sound is both an objective and subjective notion and one must use criteria that take account of these two characteristics.

Criteria chosen for measurement of sounds:

• Sonia
• The sound level
• The overall noise level

The energy of a sound is proportional to its level and duration, in the same way as the damage caused by a burn is proportional to the duration of exposure and the intensity of the radiation.
These two parameters must therefore be taken in to account. For this purpose, an A-weighted equivalent continuous sound pressure level is defined, rated LAeq, which takes account of the duration of exposure to the noise. Indeed, high-level sudden sounds (130 dB) can be tolerated without harm, whereas prolonged exposure to levels exceeding 85 to 90 dB(A) endanger hearing.