Re: Chimes; Waves in Pipes, Rods, Bars, etc

[forinas@indiana.edu (kyle forinash)]

Two things you should be aware of (in case you aren't already):

1) The wavelengths of vibration on a tube or rod do NOT obey simple rules
like those for a streched string. It is much more complicated.

2) The frequencies of vibration which are produced by a rod, pipe etc. do
not NECESSARILY correspond to the pitches you will hear. This is because of
something refered to in the literature as the 'missing fundamental'.
Apearently the ear can be fooled into 'hearing' a pitch which is not
actually present: If a set of overtones occur which are multiples of a
missing fundamental the ear will often 'hear' the fundamental as if it is
actually present. This is in fact the way orchestral chimes work: they do
NOT vibrate at any frequency corresponding to the note which is heard. You
can set this up with speakers and frequency generators; set two up with
frequencies say 300hz appart and try to match a third generator to it.
Someone with a good musical ear will usually match the third generator to
300hz rather than the two frequenies actually present (NOTE: phase appears
to play a role here so it can be tricky to make this work every time). One
interesting thing about this effect is that IT WORKS EVEN IF EACH OF THE
TWO HARMONICS GOES INTO A DIFFERENT EAR!

Have fun!
kyle

At 5:58 PM 1/1/98, brian whatcott wrote:
> At 17:23 1/1/98 -0500, Durig Lewis wrote:
> > I am considering a unit on waves and want to get my students to make wind
> > chimes and xylophones. I now realize that I don't know as much about it as
> > I used to think I did. How do I calculate the frequency of a wave in a
> > struck pipe, rod, or bar. Which plays the bigger role: the transverse or
> > the longitudinal wave in the pipe. How does the air in the pipe or around a
> > rod or bar affect the tuning. I have heard that humidity affects even the
> > tuning of a xylophone.
>
> > DurigLewis@worldnet.att.net
>
> This is the URL for a very practical piece on windchime construction:
>
> http://users.why.net/wgray/www/howto/wchime/wchime.html
>
>
> This is a public newsgroup post on chimes in transverse
> vibration, xylophone style - I think you will see how they can be
> made - quoted here without permission:
>
> **********************************************************************
> Subject:      Re: "Zen" chime question
> From:         kinsler@froggy.frognet.net (Mark Kinsler)
> Date:         1997/11/26
> Message-ID:   <65i3ut$jv6@froggy.frognet.net>
> Newsgroups:   rec.crafts.metalworking
> [More Headers]
>
>
> P'rfesser <terry.mccreary@murraystate.edu> wrote:
> > I saw a different kind of alarm clock in a catalog.  It had what the
> > catalog called a "zen chime", a metal rod suspended by two strings
> > about a quarter the length from each end of the rod.  It reminded me
> > of a similar device I saw in Hallmark.  You tap it and it seems to
> > ring for about a minute.  Very soothing.
> > Anyone know more about this:  type of rod, exactly where to support
> > it, how to maximize the ringing time, etc.?  Thanks, group.
>
> You can do this with almost any piece of metal.  A long, thin wrench works
> well.  You determine the nodes, which is where you place the
> support strings, by experiment.  Brass or bronze is
> supposed to work better than steel, but I get swell notes
> from a rather rusty piece of reinforcing rod.  Wander over to the
> music school and have a look at a vibraphone and you'll see where to
> support the bars.
>
> You can ring a lot of things.  Wood bars, of course, make a xylophone.
> Most ceramics ring well (I have to try flower pots sometime.) A tube (try
> electrical conduit) has low sectional density, which I think is why it
> will give you a very low note for its length--hence, tubular chimes.
>
>                                      Mark Kinsler
> ************************************************************************

-----------------------------------------------------
  kyle forinash   812-941-2390
  forinas@indiana.edu
  Natural Science Division
  Indiana University Southeast
  New Albany, IN    47150
  http://Physics.ius.indiana.edu/
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