How is noise perceived and measured?
Sound is vibration or waves transmitted through the air that can be perceived by ears. Sound is actually minuscule variations in air pressure, which are picked up by the tympanic membrane (eardrum). Sound has frequency and intensity. • The frequency or pitch of a sound is measured in Hertz (vibrations per second). The higher the frequency, the higher-pitched the sound; the lower the frequency, the lower-pitched the sound. • The intensity or level of sound corresponds to acoustic pressure, which is most commonly measured in decibels (dB). Because the human ear’s interpretation of sound intensity varies with the frequency of a sound, however, sound-level meters use a so-called A-weighting filter, which gives more emphasis to higher-frequency sounds than lower-frequency ones. So ambient noise is measured in A-weighted decibels, or dB(A). It is important to remember that the decibel scale is a logarithmic scale: 0 dB corresponds to the limit of audibility and 140 dB, to the pain threshold.
