Date: Tue, 30 Apr 2002 10:02:51 -0400

Author: "Jason St. John"

Subject: Re: "sound advice"


Could it be that the Doppler effect gives different perceived frequencies
in the two cases because of the difference between observing/listening
while at rest with respect to the sound-carrying medium and
observing/listening while moving through the air?

Boston University

On Tue, 30 Apr 2002, Anthony Lapinski wrote:

> I have 2 questions about sound:
> 1) Doppler effect equation for source/observer moving toward the other is
> fo = fs[(343+vo)/(343 - vs)]
> Similar equation if they recede.
> An alarm sounds. If the observer recedes, you hear a frequency. If the
> source recedes, you hear a slightly different frequency. The Doppler
> frequencies are NOT symmetrical around the alarm frequency. This can be
> seen mathematically in the equations, but is there a CONCEPTUAL
> explanation?
> 2) The speed of sound does NOT depend on its frequency. If wind is
> blowing, the wavelength changes with the speed, keeping the frequency
> constant. The same is true for refraction, like a wave going from air to
> water. But what about the temperature of the air? If the air warms up,
> speed of sound increases. Won't that INCREASE the pitch (like for the wind
> instruments), keeping wavelength constant? I know the length of the tube
> also increases, but the speed change for air is more of a factor. Am I
> missing something here is this last situation?