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Re: [Phys-l] music pipes



At 12:28 PM 4/17/2007, Anthony Lapinski , you wrote:

I am trying to categorize a list of musical (orchestral) "wind"
instruments into open and closed pipes. This also useful for math problems
involving actual instruments. Here's what I've found:

OPEN flute piccolo


CLOSED oboe clarinet saxophone trumpet bugle tuba
trombone french horn


Are there other instruments that would be considered open pipes? The list
seems like an easy task. However, in my web searches I have found much
misinformation. Some sites say a trumpet is an open pipe, while others say
it is a closed pipe! Same thing was mentioned for the oboe, bugle, and
saxophone. If the bugle is a closed pipe, then only odd harmonics can be
played. Right?

Can someone clarify/revise this information or know of a reliable
source/text/web site which lists the instruments in terms of open/closed
pipes?


For someone who is comfortable with visualizing transmission lines
it might be helpful to recall how a pulse or edge behaves at an end.
The pulse can be radiated out, reflected in phase, or reflected out
of phase. It can also be absorbed of course.

The condition for radiating a pulse is that the end impedance is a
good match to free space.
The condition for reflecting a pulse is an impedance step at the end:
a step up for phase preservation, and a step down for phase reversal.

A twin transmission line whose conductors almost touch at one end,
and has well-separated conductors at the other end, presents
an impedance ramp along the line - this reduces reflections along
the way, so that a large proportion of the signal is reflected near
the narrow end, and a large proportion radiated at the wide open end.

You may see a useful analogy here to the form of waves that occur in a wind instrument.


Brian Whatcott Altus OK Eureka!