|
Glossary of Acoustic Terms |
| 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 (20µ 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 every 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. |
|
