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WillStG
 
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Default Sound absorption in air.

Chel van Gennip wrote:
In a discussion about SACD quality here, the discussion came on absorption
of sound in air. We found some references for this absorbtion that might
be interesting in general:
http://www.sensorsmag.com/articles/0...299/main.shtml I thin the
http://www.ktu.lt/ultra/journal/pdf_...adisauskas.pdf

I used the sensorsmag data to create a table of sound absorption for the
audible range: http://www.serg.vangennip.com/absorption.pdf

It is indeed more than you expect. For a living room situation I see about
3 db for 20 kHz at 4m. For a concert hall situation I see 20dB loss for
20kHz at 28m. I am afraid there are no fast transients or extremely high
frequencies for sound in a real life concert hall.

From real life we know high frequencies are absorbed, just look at the
sound of a thunderstorm passing by, the sound of fireworks nearby and high
in the air, the sound distribution on open air festivals. It is however
more than you expect.


Well - IIRC my first audio book bascially said something about
the "roll off point" of sound being absorbed in air is around 6kHz.
Where that roll off point is may be a bit more important as a practical
matter than an exact calculation of how far down 20Khz is at 28 meters
I think; if the diffuse sound is greater than the direct sound where
you place your mic no amount of high end boost is really going to
"equalize" the difference much and bring the source closer, no? But in
the direct field you can compensate for air absorbtion somewhat with
eq, and get a bit more "reach" I think.

For a TV application example if a lavalier mic is a bit too far
from someone's mouth than I'd prefer, I might tweak up 5-6kHz a bit to
compensate for the distance, and maybe add a bit of low end as well to
compensate for the loss of any desirable "proximity effect" bass you
get when the mic is closer to an anchor's mouth.

Will Miho
NY Music and TV/Audio for Video/Live Sound Guy
"The large print giveth and the small print taketh away..." Tom Waits

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Lorin David Schultz
 
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Default Sound absorption in air.

"WillStG" wrote:

For a TV application example if a lavalier mic is a bit too far
from someone's mouth than I'd prefer, I might tweak up 5-6kHz a bit
to compensate for the distance, and maybe add a bit of low end as
well to compensate for the loss of any desirable "proximity effect"
bass you get when the mic is closer to an anchor's mouth.



Ha! You got placebo'd! There *is* no proximity effect with a lav.
It's an omni (even the ones that claim to be cards are, let's face it,
just NOT).

I've found that with *most* anchors (there are, of course, exceptions) I
actually get better bottom by lowering the mic a little. Getting it
away from their throat gets rid of all that low-mid larynx muck while
capturing better chest resonance.

Of course, then your direct/reflected ratio goes down so you can't win.

--
"It CAN'T be too loud... some of the red lights aren't even on yet!"
- Lorin David Schultz
in the control room
making even bad news sound good

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WillStG
 
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Default Sound absorption in air.

Lorin David Schultz wrote:
"WillStG" wrote:

For a TV application example if a lavalier mic is a bit too far
from someone's mouth than I'd prefer, I might tweak up 5-6kHz a bit
to compensate for the distance, and maybe add a bit of low end as
well to compensate for the loss of any desirable "proximity effect"
bass you get when the mic is closer to an anchor's mouth.



Ha! You got placebo'd! There *is* no proximity effect with a lav.
It's an omni (even the ones that claim to be cards are, let's face it,
just NOT).


Well Jeez, neither are Omni's Lorin. As a practical excercise you
haven't experienced an Omni mic can give you more bass response when
you place it closer you get to the source? Sure an omni lavalier
rustles less and has less problem with wind noise because "omni's have
no proximity effect", but then show me a perfect omni. Why mess with
things unless I hear something I don't like?

I've found that with *most* anchors (there are, of course, exceptions) I
actually get better bottom by lowering the mic a little. Getting it
away from their throat gets rid of all that low-mid larynx muck while
capturing better chest resonance.


Fine, whatever works for you. I used an example that has worked
for me to get rid of "hollow" room sound and get an anchor to sound
more upfront; you can't use "equalization" to bring something in the
diffuse sound field back into the direct sound field but for something
in the direct field you can do some compensation with eq for air
absorbtion/mic distance/positioning relative to the source was my
point.

Will Miho
NY Music and TV/Audio For Video/Live Sound Guy
"The large print giveth and the small print taketh away..." Tom Waits

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Lorin David Schultz
 
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Default Sound absorption in air.

"WillStG" wrote:

Fine, whatever works for you.


Whoa, chill Will. I was just givin' you the gears a little. Absolutely
no disrespect intended. Just one old regular having fun with another
one who happens to do similar work, that's all.



I used an example that has worked for me to get rid of "hollow" room
sound and get an anchor to sound more upfront; you can't use
"equalization" to bring something in the diffuse sound field back
into the direct sound field but for something in the direct field you
can do some compensation with eq for air absorbtion/mic
distance/positioning relative to the source was my point.


Right, and I agree. I just don't accept that moving a lav closer to the
mouth will improve bass response. But I still agreed with the rest of
your post by conceding that moving the mic down to mid chest would
exacerbate room problems.

--
"It CAN'T be too loud... some of the red lights aren't even on yet!"
- Lorin David Schultz
in the control room
making even bad news sound good

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