Speed of Sound

MtnBob · 8th April 2006, 03:36 AM

Anyone know a simple way to calculate the speed of sound at different altitudes? I always see it as 341-344 m/s at sea level, but I live at 2667 m (8750 ft). Is there enough differance to matter when it comes to audio calculations (esp dipole calcs)?

rpapps · 8th April 2006, 04:24 AM

Hi
Not only affected by density (altitude) but also temperature and humidity. You may find some useful stuff here:
http://hyperphysics.phy-astr.gsu.edu...nd/souspe.html
Cheers
Rob

toxic tuan · 8th April 2006, 09:30 AM

nice.

johninCR · 8th April 2006, 10:02 AM

Bob,

Don't even worry about it. With OB, the room and floor boundaries play a much more significant role that calculations, spreadsheets, etc. can be thrown out the window. I build only OB speakers and live at 1500m. The only calculation I ever use it to compute an estimated Fequal point and in room you always get more bass than that. That's the beauty of OB, no formulae etc to restrict you or tell you what to do.

Ron E · 8th April 2006, 05:12 PM

What is left out of what has been discussed so far is humidity. Humidity can have an effect on sound velocity as well as temperature and pressure.

Download Claus Futtrup's DPC calculator. He has a few text files included in the package which detail how to calculate sound speed for varying pressure and temperature and humidity.

Geek · 8th April 2006, 06:21 PM

Hmmm, I wonder how much a practical effect humidity has (I'm familiar with lab results), living in an area where 70% RH is considered a "dry day"

Ron E · 8th April 2006, 08:54 PM

It is not a lot, as a first approximation it is easily neglectable compared to temperature. The effect is there, and it gets greater with increased temperature.

T in celcius
RH in percent (relative humidity or w/ws)
c=speed of sound in m/s

I have a tool to calculate:
T=0, Rh=0 - c=331.4
T=0, Rh=100 - c=330.8
so ~0.3% difference

T=40, RH=0 - c=354.8
T=40, RH=100 - c=347.9
so ~2% difference

MtnBob · 9th April 2006, 04:14 AM

Thanks all for the replies. I'm inclined to be more like johninCr and go mostly by ear, but I'll check the other stuff too, just to satisfy my curiosity mainly.
Wow, Geek, here a dry day is when it's single digits humidity.

Geek · 10th April 2006, 11:39 PM

Quote:

Originally posted by MtnBob
Wow, Geek, here a dry day is when it's single digits humidity.

Let's just say that if mildew was ever an economically viable substance, we folk in the Fraser Valley would be richer than the Saudi's

8th April 2006, 03:36 AM	#1
MtnBob diyAudio Member Join Date: Dec 2003 Location: 8800 ft above sea level	Speed of Sound Anyone know a simple way to calculate the speed of sound at different altitudes? I always see it as 341-344 m/s at sea level, but I live at 2667 m (8750 ft). Is there enough differance to matter when it comes to audio calculations (esp dipole calcs)? __________________ "Whenever you find you are on the side of the majority, it is time to pause and reflect." Mark Twain

8th April 2006, 04:24 AM	#2
rpapps diyAudio Member Join Date: Jul 2004 Location: nowhere of interest	Speed of sound Hi Not only affected by density (altitude) but also temperature and humidity. You may find some useful stuff here: http://hyperphysics.phy-astr.gsu.edu...nd/souspe.html Cheers Rob

8th April 2006, 10:02 AM	#4
johninCR diyAudio Member Join Date: Apr 2004 Location: Costa Rica	Bob, Don't even worry about it. With OB, the room and floor boundaries play a much more significant role that calculations, spreadsheets, etc. can be thrown out the window. I build only OB speakers and live at 1500m. The only calculation I ever use it to compute an estimated Fequal point and in room you always get more bass than that. That's the beauty of OB, no formulae etc to restrict you or tell you what to do. __________________ Everyone has a photographic memory. It's just that most are out of film.

8th April 2006, 05:12 PM	#5
Ron E diyAudio Member Join Date: Jun 2002 Location: USA, MN	What is left out of what has been discussed so far is humidity. Humidity can have an effect on sound velocity as well as temperature and pressure. Download Claus Futtrup's DPC calculator. He has a few text files included in the package which detail how to calculate sound speed for varying pressure and temperature and humidity. __________________ Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan Science is a way of thinking much more than it is a body of knowledge. --Carl Sagan

8th April 2006, 08:54 PM	#7
Ron E diyAudio Member Join Date: Jun 2002 Location: USA, MN	It is not a lot, as a first approximation it is easily neglectable compared to temperature. The effect is there, and it gets greater with increased temperature. T in celcius RH in percent (relative humidity or w/ws) c=speed of sound in m/s I have a tool to calculate: T=0, Rh=0 - c=331.4 T=0, Rh=100 - c=330.8 so ~0.3% difference T=40, RH=0 - c=354.8 T=40, RH=100 - c=347.9 so ~2% difference __________________ Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan Science is a way of thinking much more than it is a body of knowledge. --Carl Sagan


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8th April 2006, 09:30 AM	#3
toxic tuan diyAudio Member Join Date: Apr 2006 Location: southern california	nice.

8th April 2006, 06:21 PM	#6
Geek diyAudio Member Join Date: Sep 2004	Hmmm, I wonder how much a practical effect humidity has (I'm familiar with lab results), living in an area where 70% RH is considered a "dry day"

9th April 2006, 04:14 AM	#8
MtnBob diyAudio Member Join Date: Dec 2003 Location: 8800 ft above sea level	Thanks all for the replies. I'm inclined to be more like johninCr and go mostly by ear, but I'll check the other stuff too, just to satisfy my curiosity mainly. Wow, Geek, here a dry day is when it's single digits humidity. __________________ "Whenever you find you are on the side of the majority, it is time to pause and reflect." Mark Twain

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