Definitions, Terms, Units and Parameters
Frequency Weightings are applied by sound level meters to correlate the measurement closer to the human response.
A-weighting: the human ear is frequency selective. Between 500 Hz and 6 kHz the ear is very sensitive but less so at lower and higher frequencies. The A-weighting filter covers the full audio range - 20 Hz to 20 kHz and the shape is similar to the response of the human ear at the lower levels - see the equal loudness entry.
A-weighted noise measurements are the most widely used ** and the Class of the meter reflects the accuracy of the meter including the filters. .
The preferred convention is to write LA = x dB, however dBA, dB(A) or dBA are often used to indicate A weighted measurements. as are LAeq, LAmax etc.,
** A weighted measurements only correlate well with the perceived loudness at low sound levels, as originally intended, so many people object to the general use, often supported by regulations. Low frequency noise, which disturbs many people, is suppressed by A weighted meters. Currently thousands of wind turbines being built in rural areas are highlighting this low frequency anomaly.
B-weighting: no longer in common use, was used by the motor industry for many years. The B-weighting was more critical of lower frequencies than the A-weighting network.
C-weighting: a standard frequency weighting for sound level meters, commonly used for higher level measurements and Peak - Sound Pressure levels. Approximately follows the 100 phon curve - also written as dB(C) or dBC.
The A-weighting curve is used extensively for general purpose noise measurements but the C-weighting correlates better with the human response to high noise levels
D-weighting: sound level meter frequency weighting developed for measuring high level aircraft noise especially non-bypass military engines. No longer in common use since IEC 61672 2003 . Later ISO standards recommend A-weighting for commercial aircraft noise
Flat weightinga sound level meter weighting based on an amplitude-frequency characteristic that is flat over a frequency range that must be stated. No longer appears in the Standards, which prefer the newer Z-weighting
L, Lin, and Linear Weighting: all values are weighted equally in the specified range, now largely superseded by the Z-weighting
Z-weighting: Z for 'Zero' frequency weighting implies no frequency weighting, 10 Hz to 20 kHz ±1.5 dB.
Equivalent to the older Linear, LIN or Flat terms - alternatives dB(Z) and dBZ
The Z- or Zero frequency weighting was introduced (IEC 61672 2003) to replace the Flat or Linear Filters
See other examples of Z-weighted information LZeq, LZF, LZS etc..
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