# Acoustic Terms Glossary

## Glossary of Terms for Acoustics

A guide to most commonly used acoustic terms used for noise and sound measurement found in sound level meters.

 Decibels dB Ten times the logarithm (to base 10) of the ratio of two mean square values of sound pressure. Frequency Hz The number of cyclical variations per unit time Octave Bands Hz Frequency ranges in which the upper limit of each band is twice the lower limit. Octave bands are identified by their geometric mean frequency or centre frequency. Sound Power W The acoustic power of a sound source expressed in Watts. Sound Power Level Lw The acoustic power radiated from a given sound source as related to a reference power level. Sound Pressure P Fluctuations in air pressure caused by the presence of sound waves. Sound Pressure Level Lp The ratio expressed in dB of mean-square sound pressure to a reference mean-square pressure which, by convention, has been selected to be equal to the assumed threshold of hearing (20Âµ Pa). Spectrum A term that refers to the frequency response. Weighting Network dB(A) An electronic filter in a sound level meter which approximates, under defused conditions, the frequency response of the human ear. The ‘A’ weighting network is the one most commonly used. Equivalent Continuous Sound Pressure Level Leq The equivalent continuous level which is a measure of the energy content of a sound over a time period. It gives a single figure expressing the equivalent of a varying level. It is an energy average. Dose D Noise dose is a percentage number. Depending on a criterion level and exchange rate (eg 90dB and 3 – 100% Dose = 90dB for 8 hours). Dose per Hour DOHR Designed to show the Dose exposure over each hour. Projected Dose Proj D Projected dose allows the present accumulated dose, over the present logged time duration, to be projected forward to give the predicted 8 hour period. Noise Exposure Lex Personal noise exposure (also known as Lepd), usually referred to a daily 8 hour rate. Percentile Ln The dB level exceeded for n% of the time.

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