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Re: [Phys-L] sound



On 04/13/2013 10:09 AM, Dan Beeker wrote:

Keep in mind that a musical instrument is far different from a simple
pipe. It is much like comparing apples and oranges. Still a good
model is to start with a pipe, closed at the mouthpiece end, open at
the other end. This gives odd harmonics. The trick is to move the
harmonics around so they look like even harmonics. So, add a
mouthpiece. The biggest effect is it adds a filter so the high
frequency harmonics are reduced. Just as important it shifts the high
harmonics down in frequency. Then add a bell. The bell operates on
the lower frequencies and shifts them up. If you get the right
combination, you get a series of harmonics that looks like on open
pipe and the contraption becomes a musical instrument.

Also, obviously, the bell serves to provide impedance matching, making
the instrument more directional and louder, yet less sharply resonant.
The exponential horn on a bullhorn or even a passive megaphone would
ideally produce no resonance at all -- just impedance matching.

More importantly: Again I recommend the UNSW site.

For example, all of the points made above, and more, are discussed at
http://www.phys.unsw.edu.au/jw/brassacoustics.html
especially
http://www.phys.unsw.edu.au/jw/brassacoustics.html#bells
with background information at
http://www.phys.unsw.edu.au/jw/pipes.html
et cetera.

The discussion includes diagrams and audio clips. The level of presentation
is that of an expert talking to a non-expert. For example, mode locking is
not discussed in any detail, but the term is /mentioned/, so you know what
to search for if you want more information.


There are several references that may help you out. Each has useful
tidbits but I have not seen a completely coherent explanation in any
of the standard texts that gives a simple explanation for the student
and still satisfies the person truly knowledgeable in acoustical
physics though some come close. Donald hall's "Musical Acoustics"
chapter 13 isn't a bad place to start. Benade, "The Physics of
Brasses" Scientific Amarican 1973 is useful. Fletcher and Rossing
"The Physics of Musical Instruments" chapter 14 is excellent for a
starting point - but not for the mathematically naive.

Fletcher and Rossing is legendary. Read the reviews at
http://www.amazon.com/Physics-Musical-Instruments-Neville-Fletcher/dp/1441931201