I remember from my days as a traveling musician playing saxophone and
"metal" flute on the road, that when the instruments were cold they would
play flat. As they warmed up they would go sharper and sharper. Since
different musicians instruments swell at different rates, the ensemble
would have a hell of a time playing in tune during the temperature
transition. That was because the metal had contracted due to the cold and
therefore the bores were larger. When the instruments warmed up, the metal
expanded, thus reducing the bore size and the pitch increased--not because
warm air increases pitch but because the bore was smaller. I don't have my
acoustics books here at home with me, and I'm not a physics of sound
specialist, but I'm quite sure that the speed of sound (how fast the waves
are propagated through the air) and pitch (the wave-lengths) are not
related. I'm also sure that the speed of sound decreases when propagated
through moist warm air (like on a lazy summer day) and speeds up when
propagated through dry cold air. Try this for an experiment. Sing a long
held tone inside your house at indoor temperature and note the pitch, then
continue singing and immediately go outside on a cold day when the weather
is close to freezing and the air is dry and note the pitch. The sound
travels faster through the cold dry air (that is why walking on snow sounds
so crisp on frigid days), so the sound should seem as if it is clearer and
psychoacoustically louder, but the pitch should stay exactly the same. If
wave-length (pitch) and wave-speed (speed of sound) were related you would
notice a pitch difference in the cold air. This has nothing to do with the
fact that warm air from your lungs is propagating the sound, since your
voice will be heard all over the neighborhood as a result of cold air
propagating the waves. If you cannot hold a steady pitch, use a boom-box
or a tuning fork for the test.
At 11:31 PM 12/12/2001 +0900, you wrote:
>Paul,
>
> >Perhaps
> > this a question which the more physics and acoustics literate folk out
> > there can shed more light on.
>
>
>http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe.html?tc=40&tf=&v=&vc
>=&vm=
>
>gives the relationship of temperature and speed of sound. You need java
>enabled. Enter the Centigrade number and then tab to get the other values.
>
>At 10 degrees C (50F) the speed of sound is 337.5 m/s. At 30C (86F) it's
>349.7 m/s--an increase of 3.6 %. The speed of sound is directly related to
>pitch and any percentage change in speed of sound equals the same percentage
>change in pitch. 3.6% is a little over a half note difference.
>
>Nelson Zink
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