[Scott Dorsey]

Richard Webb wrote:
On Tue 2011-Jul-05 13:38, William Sommerwerck writes:

Would you care to expound on when one might use a
weighted and when C weighted, since that would be his next
question, and would probably be beneficial? In fact, if we
were still updating the FAQ that might be a good addition.

As I and others said, the A weighting mimics the response of the ear
at low levels. That should be self-explanatory.

INdeed, but you probably wouldn't be surprised at the number of times I've seen, both in this group, and in
alt.audio.pro.live-sound folks asking which scale to use on
their rat shack meter they bought to see how loud the band
is at foh position g. From the nature of the questions
the op usually asks I figured Scott was a good one to
expound on the subject a bit, because he goes into enough
detail that the neophyte can understand it. YOu and I both
have the habit of assuming folks understand what they really don't.
NEither one of us were cut out to be teachers methinks g.

The problem is, I used to know the answer, but I am less and less sure.

The A weighting is supposed to measure the audibility of a sound, but
in fact that's not really as useful as you think. It is a very poor
measure of the annoyance level of a sound or of the hazard level of it.

The C weighting is supposed to be as close to flat as was possible with
a particular kind of ceramic microphone that no longer exists. Modern
meters (which are capable of much better low frequency response) are
basically handicapped by making them match up to the C weighting.
It's probably a better measure of the annoyance level of a sound.

BUT, the noise ordinances in most cities are based on A-weighted
measurements. Maybe this is because of lobbying from nightclub owners
whose clubs leak a lot of low end. Maybe it's because the A-weighting
is intended to measure audibility. But it makes those ordinances useless
against low frequency sources (like stamping mills and nightclubs).
However, determining legality under those ordinances is probably the only
good use for A-weighting these days.

Really, neither one of them do what people want them to do today.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."