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Glossary of common noise definitions

20 December 2017

NOISE – Glossary

Useful Common Used Sound Definitions

 

Standard definitions

SPL: Sound Pressure Level

Leq: Equivalent sound level. Average logarithmic level during a measurement period. The measurement period should be indicated, it should also include other descriptors i.e. A, C, or Z weightings and F, S or I Time Constants.

Lmax : Maximum Sound Level a maximum level during a measurement period or a noise event, not the same as peak. Also includes other descriptors i.e. A, C, or Z weightings and F, S or I Time Constants. Sometimes written as Max dB(A), see also LAmax

Lmin : Minimum Sound Level during a measurement period or a noise event.
Includes other descriptors i.e. A, C, or Z weightings and F, S or I Time Constants. 
Sometimes written as Min dB(A).

Lpeak : Lpk - Peak Sound Level

 

Weighting definitions

A-Weighting

The most common weighting that is used in noise measurement is A-Weighting. Like the human ear, this effectively cuts off the lower and higher frequencies that the average person cannot hear.

Defined in the sound level meter standards (IEC 60651, IEC 60804, IEC 61672, ANSI S1.4).  A-weighted measurements are expressed as dBA or dB(A).

C-Weighting

The response of the human ear varies with the sound level. At higher levels, 100 dB and above, the ear's response is flatter, as shown in the C-Weighted Response curve in figure 2. Although the A-Weighted response is used for most applications, C-Weighting is also available on our Norsonic and Sonitus Sound level meters. C-Weighting is usually used for Peak measurements and in some entertainment noise measurement, where the transmission of bass noise can be a problem. C-Weighted measurements are expressed as dBC or dB(C).

Z-Weighting

Z-weighting is a flat frequency response of 10Hz to 20kHz ±1.5dB. This response replaces the older "Linear" or "Unweighted" responses as these did not define the frequency range over which the meter would be linear. Z-weighted measurements are expressed as dBZ or dB(Z). Z-weighted data can easily be converted into either A or C weighted.

 

Statistics

Ln: percentile level where 'n' is between 0.01 and 99.9% calculated by Statistical Analysis.

Usually include a descriptor i.e. A-weighting. Most common Ln values are LA10 and LA90 levels.

 

LA10 the noise level just exceeded for 10% of the measurement period, A-weighted and calculated by Statistical Analysis.

LA90 the noise level exceeded for 90% of the measurement period, A-weighted and calculated by Statistical Analysis.

The LA10 and LA90 are extensively used for rating traffic noise and Background Noise respectively.
The measurement period should also be stated. For example, LA10 (18-hour) is considered good practice when reporting Road Traffic Noise measurements.

 

Other useful definitions

Lden : Day-evening-night equivalent level A-weighted, Leq. Sound Level, measured over the 24-hour period, with a 10dB penalty added to the levels between 23.00 and 07.00 hours and a 5 dB penalty added to the levels between 19.00 and 23.00 hours to reflect people's extra sensitivity to noise during the night and the evening.

Lp : Sound Pressure Level

LW: Sound Power Level

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