The human ear is frequency selective. Between 500 Hz and 6,000 Hz our ears are very sensitive compared with the lower and higher frequencies. The full range for young people is 20 to 20,000 Hz.
This subjective response is also loudness dependent and as a result early sound level meters included A, B, C and Linear or Flat settings to 'correlate' the objective meter readings with the very wide subjective human response
A-weighted noise measurements are widely used and the meter class confirms the accuracy of the meter including the filters.The preferred convention is to write LA = x dB, however dBA and dB(A) are often used, as are LAeq, LAmax etc., for more information on the dB (decibel) click here
A weighted measurements correlate well with the perceived loudness at low sound levels, as originally intended. However the current use of the A-weighting for most noise applications, supported by regulations, does cause concern in some quarters. For example low frequency noise, which disturbs many people, is suppressed by A-weighted meters. Currently there are thousands of wind turbines, built in quiet rural areas, which are highlighting this low frequency anomaly.
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.
No longer in common use since IEC 61672 2003. More recent ISO standards recommend A-weighting for commercial aircraft noise.
Introduced in 2003 (IEC 61672) to replace the Flat or Linear Filters.
Written as dB(Z) or dBZ, see other examples of Z-weighted information LZeq, LZF, LZS, etc.