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Old 8th April 2006, 02:36 AM   #1
MtnBob is offline MtnBob  United States
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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)?
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Old 8th April 2006, 03:24 AM   #2
rpapps is offline rpapps  Antarctica
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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
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Rob
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Old 8th April 2006, 08:30 AM   #3
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nice.
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Old 8th April 2006, 09:02 AM   #4
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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.
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Old 8th April 2006, 04:12 PM   #5
Ron E is offline Ron E  United States
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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.
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Old 8th April 2006, 05:21 PM   #6
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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"
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Old 8th April 2006, 07:54 PM   #7
Ron E is offline Ron E  United States
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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
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Old 9th April 2006, 03:14 AM   #8
MtnBob is offline MtnBob  United States
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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.
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Old 10th April 2006, 10:39 PM   #9
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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
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