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Speed of Sound and Air Conditions
Name: Dee W.
Status: other
Age: 50s
Location: N/A
Country: N/A
Date: Thursday, November 28, 2002
Question:
Everything else being equal, does sound travel better
(meaning here,louder) when the air is humid or not?
Ditto, when the air is hot versus cool?
Ditto, when the barometric pressure is high or low?
We have gotten much confusion over whether air density a) helps sound
travel louder (as measured by decibels at recipient) because more
molecules to travel through or b) hurts sound volume because of resistance
and drag -- this is all from what started as "simple" science
project. Any help will be much appreciated. Cannot seem to find answers
to these basics anywhere in texts or Internet.
Replies:
Your topic is like "The Normandy Invasion" -- starts off "simple" and
turns into a massive undertaking. Your failure to find web sites may have
been due to a common problem -- You did not select the key search terms. You
are asking about the attenuation of sound, not its speed, which is a factor
but not the only one. Search these terms: "acoustic attenuation" "sound
attenuation" "acoustic impedance"
"sound impedance" and you will find a number of sites that discuss the
topic(s). Here are some I found.
GENERAL
http://www.pa.op.dlr.de/acoustics/acoustics_content.html
LARGE SITE, MANY LINKS
http://www.ndt-ed.org/index_flash.htm
SOUND ATTENUATION
http://www.silex.com/pdfs/Sound%20Attenuation.pdf
INCLUDES A CALCULATOR FOR VARIOUS MEDIA
http://www.cnde.iastate.edu/ncce/UT_CC/Sec.2.6/Sec.2.6.html
Vince Calder
FOLLOW UP ON THIS INQUIRY, FOUND AN EXTENSIVE ONLINE TEXT ON THE SUBJECT OF
ACOUSTIC ATTENUATION
http://www.sfu.ca/sonic-studio/handbook/index.html
Vince Calder
Dear Dee,
Here is a quick answer to your questions from Paul G. Hewitt's book,
Conceptual Physics, fourth edition, copyright 1981.
"The speed of sound depends on wind conditions, temperature, and humidity.
It does not depend on the frequency of sound; all notes travel at the same
speed. The speed of sound in dry air at 0 degrees C is about 330 meters per
second, nearly 1,200 kilometers per hour. Water vapor in the air increases
this speed slightly. Sound travels faster through warm air than through
cold air. This is to be expected because the faster-moving molecules in
warm air bump into each other more often and therefore transmit a pulse in
less time. For each degree rise in temperature above 0 degrees C, the speed
of sound in air increases by 0.6 meters per second. In water, sound travels
about four times as fast as it does in air, while in steel, the speed of
sound is about fifteen times as great as in air."
You might be able to find this textbook in your local library. I have also
found the web site Askjeeves.com to be a reliable source for answers to
science questions. It usually can provide links to reliable web sites.
Good luck on your "sonic" adventure.
Martha Croll
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