Weighting Curves

[museav]

You often see references to 'weighted' sound levels, such as A-weighted sound pressure levels. What is the purpose of these weightings? Why would you use one weighting versus another? How might they affect a single number sound pressure level measurement?

 

[seanandkate]

As I understand it, the A-weighting tries to match the curve response of human hearing, reducing the levels that the ear doesn't hear that well. BUT apparently it works best for metering environments below, say, 80dB, because it rolls off the lower frequencies so dramatically. For theatrical purposes, the C-weighted is better because the response is better in the high and (especially) low ends, and is more representative in environments above 80dB (where not taking into account lower frequencies would give a lower reading). Unweighted is a flat response.

 

[museav]

Definitely along the right lines. Think about how "the levels that the ear doesn't hear that well" relate to perceived loudness, sound pressure level and frequency.

FWIW, unweighted has long been called "flat" but for a few years now has been referenced as the Z or Zero weighting in international standards.