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Re: Impedance &c.



Fletcher and Rossing do a nice job of discussing acoustic impedance matching
in their book, "The Physics of Musical Instruments". I find acoustic
analogies are useful in getting the students to develop a "feel" for what is
going on here. That happens to tie in to what I do in our speed of sound lab
(the last one of the first semester, using a resonant air column over
adjusted water height in a tube) in which I mention the "phantom pipe" effect
just past the end of the resonating air column. From there we mention French
horns and wa-wa mutes then call it a semester while we're all in a cheery
mood.

Also, as I recall, there was a video, perhaps a segment in "The Mechanical
Universe", in which the presenter came in with a DIY horn kit. He added
sections of tubing for various effects (neat comparison of straight versus
bent tubing!) including the addition of a bell at the "discharge" end of the
horn.

Since this is an Introductory Physics class, I don't get into the DiffEq's but
stick with conceptual analogies.

Jim

On Thursday 2004 January 08 10:48, Wolfgang Rueckner wrote:
....
For sound propagation, the impedance of an air column in an acoustic
tube, for example, would be the ratio of the driving force of the
sound-producing diaphragm or piston to the resulting velocity of the
layer of air adjacent to the vibrating surface and their product
would be the power.
....
--
James R. Frysinger
Lifetime Certified Advanced Metrication Specialist
Senior Member, IEEE

http://www.cofc.edu/~frysingj
frysingerj@cofc.edu
j.frysinger@ieee.org

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