To approximate the integration time of our hearing system, sound pressure meters have a standard Fast response time, which corresponds to a time constant of 0.125 s. Consequently, in calculating some measures of noise, the instantaneous pressure fluctuations must be integrated over some time interval. The sound pressure levels of most noises vary with time. A more technical definition of sound pressure level is found in the glossary. Because the human ear can detect a wide range of sound pressure levels (10–102 Pascal (Pa)), they are measured on a logarithmic scale with units of decibels (dB). Thus, the sound pressure level indicates how much greater the measured sound is than this threshold of hearing. ![]() All measured sound pressures are referenced to a standard pressure that corresponds roughly to the threshold of hearing at 1 000 Hz. The sound pressure level is a measure of the air vibrations that make up sound. Technical definitions are found in the glossary in Appendix 3. Ford (1987) gives a more extensive review of various environmental noise measures. ![]() They are all derived from overall sound pressure levels, the variation of these levels with time and the frequency of the sounds. Most environmental noises can be approximately described by one of several simple measures. Sound transmission into and within buildingsĢ.1 Basic Aspects of Acoustical Measurements.Source Characteristics and Sound Propagation. ![]()
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