"Chris Whealy" wrote in message
...
Chel van Gennip wrote:
http://www.sensorsmag.com/articles/0...299/main.shtml I thin the
http://www.ktu.lt/ultra/journal/pdf_...adisauskas.pdf

Other references:

http://www.csgnetwork.com/atmossndabsorbcalc.html
http://www.measure.demon.co.uk/Acous...e/iso9613.html

Both based on ISO 9613 - 1

(gives the absorbtion of sound by air near STP as about 0.5 dB/meter at 20
KHz)

http://www.earthworksaudio.com/tech/hf_sound.pdf

(A hi rez advocate gives the absorbtion of sound by air near STP as about
0.068 dB/meter at 20 KHz - note this implies RH ~= 0%)

http://www.rfcafe.com/references/gen..._still_air.htm

(gives the absorbtion of sound by air near STP as about 0.563 dB/meter at 20
KHz)

http://www.grc.nasa.gov/WWW/Acoustic...nts/PDF/A7.pdf

(NASA recomends raising the frequency of disturbing sounds to exploit the
additional absorbtion of air at high frequencies)


Both of these articles are discussing air absorption in the context of
ultrasonic transducers.

So what do we call a loudspeaker or mic operating above 20 KHz, if not an
"ultrasonic transducer".

Does 40 or 50 KHz change between being ultrasonic and sonic depending on
whether its being used to clean false teeth or reproduce the sound of some
musical instrument via a SACD or DVD-A?

I think not! ;-)

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.

Now you've switched context and are referring to losses in the audible
frequency range (i.e. not ultrasonic).

Many of the sources I cited provide data for a range of audible and
ultrasonic frequencies. Introducing ultrasonic frequencies is clearly
on-topic because reproduction of ultrasonic frequencies is a heavily
promoted so-called advantage of so-called "high rez" media such as DVD-A and
SACD.


For all practical (read audible) purposes, the absorption of sound by air
is not significant for indoor listening situations.

Can you honestly say that after checking the "other references" I provided
above?