frequency response of air

mikelm · 29th February 2004, 10:52 AM

Does anyone know the frequency response of air and formulas that describe it ?

I was thinking about how much attenuation at different frequencies and different distances from a sound source

mike

sreten · 29th February 2004, 11:12 AM

Farfield nearly all sound sources will follow the inverse square law,
this dominates any attenuation or frequency dependent losses.

sreten.

mikelm · 29th February 2004, 11:54 AM

OK sure, but I wondered within this, wether some frequecies that are attenuated more that others due to the charactoristics of the air.

By way of example, I get the feeling that square wave leading and perhaps trailing edges will be softened with distance.

mike

sreten · 29th February 2004, 02:52 PM

Its the different speed of sound through air at different densities
that effectively kills high frequencies through phase interference
and frequency spreading.

A sharp lightening transient will be spread by the different
speeds of sound in the various atmospheric layers, as it
spreads its frequency components wil continually lower,
giving only the rumble effect at long distances.

sreten.

Christer · 29th February 2004, 02:55 PM

I also think the humidity of the air matters, or at least I get the
impression that higher frequencies are more attenauted when
it is very humid.

Sch3mat1c · 29th February 2004, 07:15 PM

I think he wants to know about ultrasonics. Like, are they attenuated any more than otherwise?

Speaking of which, something I've always wondered is just how high a frequency can be transmitted acoustically - I know over 100kHz exists!

Tim

Christer · 29th February 2004, 07:19 PM

Quote:

Originally posted by Sch3mat1c

Speaking of which, something I've always wondered is just how high a frequency can be transmitted acoustically - I know over 100kHz exists!

Unless I misremember the figures 300kHz obviously works well
John Iversons ultrasonic speakers?

mikelm · 29th February 2004, 08:04 PM

Quote:

Originally posted by Sch3mat1c
I think he wants to know about ultrasonics. Like, are they attenuated any more than otherwise?

Not exclusively,

Ideally I would like to see frequency response graphs

10hz - 100khz

at 1 meter, 2m, 3m, 4m, 5m.

what happens to a square wave leading edge would also be interesting.

Bill Fitzpatrick · 29th February 2004, 08:17 PM

Quote:

Originally posted by mikelm

what happens to a square wave leading edge would also be interesting.

Finding the transducer for this would be quite a challenge!

29th February 2004, 10:52 AM	#1
mikelm diyAudio Member Join Date: May 2003 Location: England	frequency response of air Does anyone know the frequency response of air and formulas that describe it ? I was thinking about how much attenuation at different frequencies and different distances from a sound source mike

29th February 2004, 07:15 PM	#6
Sch3mat1c diyAudio Member Join Date: Jan 2003 Location: Milwaukee, WI	I think he wants to know about ultrasonics. Like, are they attenuated any more than otherwise? Speaking of which, something I've always wondered is just how high a frequency can be transmitted acoustically - I know over 100kHz exists! Tim __________________ See my Electronics webpage -- the home of Vacuum Tube Drag Racing. The key to being a successful Audiophile: "I reject your reality and substitute my own!"

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29th February 2004, 11:12 AM	#2
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Farfield nearly all sound sources will follow the inverse square law, this dominates any attenuation or frequency dependent losses. sreten.

29th February 2004, 11:54 AM	#3
mikelm diyAudio Member Join Date: May 2003 Location: England	OK sure, but I wondered within this, wether some frequecies that are attenuated more that others due to the charactoristics of the air. By way of example, I get the feeling that square wave leading and perhaps trailing edges will be softened with distance. mike

29th February 2004, 02:52 PM	#4
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Its the different speed of sound through air at different densities that effectively kills high frequencies through phase interference and frequency spreading. A sharp lightening transient will be spread by the different speeds of sound in the various atmospheric layers, as it spreads its frequency components wil continually lower, giving only the rumble effect at long distances. sreten.

29th February 2004, 02:55 PM	#5
Christer diyAudio Member Join Date: Sep 2002 Location: Sweden	I also think the humidity of the air matters, or at least I get the impression that higher frequencies are more attenauted when it is very humid.

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