The ‘A’ frequency weighting suggests that if a tone of 40 dB is played at 1000 Hz, a 40 dB tone played at
63
Hz would sound 26 dB quieter, or be 14 dB(A). Due to its simplicity and convenience, the ‘A’ frequency
weighting has become popular and is now used for many different noise sources at different levels.
In fact, most legislation regarding noise is written using dB(A)s, in addition nearly all manufacturers
of
fans and other noise generating machines quote their noise levels in dB(A)s at 1, 1.5, or 3 metres
assuming
spherical distribution. It is therefore important that we understand the ‘A’ frequency weighting and how
dB(A)s are calculated.