Is there a quick and dirty explanation of the difference between
A-weighting and C-weighting on a decibel meter? What I'm trying to
figure out is what weighting to use if I'm trying to keep a concert
down to a certain level.

Do a search on this group. There are several good threads concerning A
and C weighting on SP meters.

Oh, you're right. Thanks.

Nat wrote:
Is there a quick and dirty explanation of the difference between
A-weighting and C-weighting on a decibel meter? What I'm trying to
figure out is what weighting to use if I'm trying to keep a concert
down to a certain level.

This is discussed in the FAQ. The A weighting basically does not take
low end information into account (because it basically models the sensitivity
of human hearing at moderate levels).
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

"Nat" wrote in message
oups.com...
Is there a quick and dirty explanation of the difference between
A-weighting and C-weighting on a decibel meter? What I'm trying to
figure out is what weighting to use if I'm trying to keep a concert
down to a certain level.


Basically, "A" weighting rolls off the lows and is calibrated toward the
midrange frequencies to which people's ears are more sensitive. "C"
weighting rolls off at a much lower frequency so it includes bass
frequencies. When dealing with music, a "C" weighted meter will read higher
than an "A" weighted meter will for the same music. Which weighting you need
to use will depend on why you need to keep the music down. This is an
oversimplification, but for inside the area where the concert is taking
place you might want to use the "A" weighting, while if the objective is to
keeping your neighbors from complaining, the "C" weighting might be better
since the low frequencies tend to carry further and penetrate more walls and
the "A" weighting largely ignores those low frequencies. OSHA regulations
for workplace noise use the "A" weighting, I believe.

In article .com,
"Nat" wrote:

Is there a quick and dirty explanation of the difference between
A-weighting and C-weighting on a decibel meter? What I'm trying to
figure out is what weighting to use if I'm trying to keep a concert
down to a certain level.

The basic notion is that the human auditory system has a different
response (bandpass) at low sound pressure levels than at higher levels.
At low levels, very low and very high frequencies are not perceived as
well.

"A" weighting reduces the sensitivity of the measuring instrument at
very low and very high frequencies, compared to "C" weighting,
more-or-less the same way that the human auditory system does.
Therefore, use "A" weighting for low-level sound fields, and "C" for
higher level fields, if you want to get an idea of how humans will
perceive the situation.

When to use "A" and when to change to "C"? Take a look at the
Fletcher-Munson curves.

Isaac

Nat wrote:

Oh, you're right. Thanks.

And extra points for spelling you're correctly.

Ian
--
Ian Bell

"Nat" writes:

Is there a quick and dirty explanation of the difference between
A-weighting and C-weighting on a decibel meter? What I'm trying to
figure out is what weighting to use if I'm trying to keep a concert
down to a certain level.

Here is one explanation from Rane Pro Audio Reference
http://www.rane.com/par-w.html#weighting_filters

A-weighting (not official but commonly written as dBA) The A-curve
is a wide bandpass filter centered at 2.5 kHz, with ~20 dB attenuation
at 100 Hz, and ~10 dB attenuation at 20 kHz, therefore it tends to
heavily roll-off the low end, with a more modest effect on high
frequencies. It is the inverse of the 30-phon (or 30 dB-SPL)
equal-loudness curve of Fletcher-Munson. [Editorial Note: Low-cost
audio equipment often list an A-weighted noise spec -- not because it
correlates well with our hearing -- but because it helps "hide" nasty
low-frequency hum components that make for bad noise specs. Sometimes
A-weighting can "improve" a noise spec by 10 dB. Words to the wise:
always wonder what a manufacturer is hiding when they use
A-weighting.]

C-weighting (not official but commonly written as dBC) The C-curve
is "flat," but with limited bandwidth, with -3 dB corners of 31.5 Hz
and 8 kHz, respectively.


--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

Oh, you're right. Thanks.

And extra points for spelling you're correctly.



You're both giving away your ages here

"Gareth Magennis" writes:

Oh, you're right. Thanks.

And extra points for spelling you're correctly.



You're both giving away your ages here

Because the vast majority of people under 30 lack grammar skills? I'll
take this embarrassment over that of being illiterate.
--
Randy Yates
Sony Ericsson Mobile Communications
Research Triangle Park, NC, USA
, 919-472-1124

Tomi Holger Engdahl wrote:

"Nat" writes:


Is there a quick and dirty explanation of the difference between
A-weighting and C-weighting on a decibel meter? What I'm trying to
figure out is what weighting to use if I'm trying to keep a concert
down to a certain level.


Here is one explanation from Rane Pro Audio Reference
http://www.rane.com/par-w.html#weighting_filters

A-weighting (not official but commonly written as dBA) The A-curve
is a wide bandpass filter centered at 2.5 kHz, with ~20 dB attenuation
at 100 Hz, and ~10 dB attenuation at 20 kHz, therefore it tends to
heavily roll-off the low end, with a more modest effect on high
frequencies. It is the inverse of the 30-phon (or 30 dB-SPL)
equal-loudness curve of Fletcher-Munson. [Editorial Note: Low-cost
audio equipment often list an A-weighted noise spec -- not because it
correlates well with our hearing -- but because it helps "hide" nasty
low-frequency hum components that make for bad noise specs. Sometimes
A-weighting can "improve" a noise spec by 10 dB. Words to the wise:
always wonder what a manufacturer is hiding when they use
A-weighting.]

Not just them. Industrial or municipal noise sources as well. I stuck
a mic outside and found a tremendous, more-or-less constant blob of
energy at 40 Hz and below, easily more than 10-dB above the rest of the
spectrum. And that's not with a measurement mic, that's with an MXL-990
which has a horrible rolloff below 100 Hz anyway (which is partly why
it's the one mic I hate enough to put out in the weather); this probably
means it's really a 20-dB peak. It looks like a mountain on the
spectrum analyzer plugin.

Municipal noise ordinances (when they have this spec) specify
A-weighting, not C, for their limits, at the property line. This noise
does not register in the A scale but there's about -55 dBC out there,
possibly from the freeway 1.5 miles away.

Given the military R&D into sonic weapons in this band, I wonder if
we're not unknowingly poisoning ourselves with LF aggravation.

S O'Neill wrote:

Not just them. Industrial or municipal noise sources as well. I stuck
a mic outside and found a tremendous, more-or-less constant blob of
energy at 40 Hz and below, easily more than 10-dB above the rest of the
spectrum. And that's not with a measurement mic, that's with an MXL-990
which has a horrible rolloff below 100 Hz anyway (which is partly why
it's the one mic I hate enough to put out in the weather); this probably
means it's really a 20-dB peak. It looks like a mountain on the
spectrum analyzer plugin.

This is basically why I can't stay in New York for more than about three
days before I absolutely have to leave and find someplace quiet. There is
just no place you can go to get away from that stuff. Even in Gabe's
mastering room I could feel the subway.

Municipal noise ordinances (when they have this spec) specify
A-weighting, not C, for their limits, at the property line. This noise
does not register in the A scale but there's about -55 dBC out there,
possibly from the freeway 1.5 miles away.

Around here the municipal code requires A-weighting, which basically makes
it useless because most of the things the legislation was put into place
to prevent are now things with primarily low end sound, like nuclear car
subwoofers and cars with damaged mufflers. I am really curious about the
history of this legislation because it seems basically like various local
governments have all been copying one another... who actually came up with
the original set of laws?

Given the military R&D into sonic weapons in this band, I wonder if
we're not unknowingly poisoning ourselves with LF aggravation.

It's by no means unknowing. Incidentally, a good overview about the history
of noise pollution is contained in _The Soundscape of Modernity: Architectural
Acoustics and the Culture of Listening in America 1900-1933_ by Emily Thompson.
It's a fun book.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

I am really curious about the
history of this legislation because it seems basically like various
local
governments have all been copying one another... who actually came up
with
the original set of laws?

As a county lawyer, I can assure you that that is true. So what would
your perfect noise legislation say? Maybe we'll kick it into effect
here the next time the issue comes up.

In article ,
(Scott Dorsey) wrote:

Around here the municipal code requires A-weighting, which basically makes
it useless because most of the things the legislation was put into place
to prevent are now things with primarily low end sound, like nuclear car
subwoofers and cars with damaged mufflers. I am really curious about the
history of this legislation because it seems basically like various local
governments have all been copying one another... who actually came up with
the original set of laws?

A lot of noise laws/noise criteria in the U.S. can be traced to research
by the EPA in the 1970's (you can see the EPA 'Levels Document' at
http://www.nonoise.org/library/levels74/levels74.htm).

Many noise ordinance use dBA because research has shown that annoyance
correlates pretty consistently with A-weighted noise metrics, even if
the source has strong low-frequency components (for example trucks and
jet takeoffs). The "Schultz Curve" (from the 1980's I think). is an
example of this - it tracks 'percent annoyed' vs A-weighted sound level.
Several subsequent studies in different parts of the world have
reaffirmed the curve.

However, more and more C-weighted-based criteria are popping up to
address low-frequency noise.

Herb

--
Herb Singleton

Sound & Vibration Measurements
http://www.cross-spectrum.com