Re: Sound absorption in air.


"Chel van Gennip"

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


** Shame your figures do not include data for 15kHz. That is the highest
frequency that is significant for most adults when music listening - ie
filtering out all above 15kHz has no audible effect.


> It is indeed more than you expect. For a living room situation I see about
> 3 db for 20 kHz at 4m.


** See: http://www.csgnetwork.com/atmossndabsorbcalc.html

For a room temp of 26C and 75% humidity, the absorption loss at 20kHz over 4
metres is only 1.3 dB.

For 15 kHz it is only 0.8 dB.


>For a concert hall situation I see 20dB loss for
> 20kHz at 28m.


** More like 11.5 dB at 20kHz.

Or 6.9 dB at 15 kHz.



> I am afraid there are no fast transients or extremely high
> frequencies for sound in a real life concert hall.


** Sure - it sounds dull in any concert hall but that has SFA to do with
absorption.

It HAS all to do with *reverberation* being the major component of sound
heard in the body of the audience.


BTW:

Most recording are made with close mic techniques, to overcome
reverberation.

The mic is in a spot no audience member ever could be.

It is *possible* for some supersonic stuff to get picked up and be recorded
on wide bandwidth gear.

But only the dogs and bats in your house will hear it.




......... Phil


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