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'pipe organ method'
1999\01\12@164113 by Peter L. Peres

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Hello,

 I know that this method seems funny (and Alice needled me) so I'm
looking at the various problems: Turns out that no-one ever heard of pipe
organs de-tuning themselves, that the resonant frequency is linearly
proportional with the column height (strictly linearly) and that very
small length changes give small but very constant frequency changes.
Atmospheric pressure and temperature do not play a role as far as pipe
organ experts know. So it should work even over changing temperature.

 My device was for lab use only, so I did not have a temperature problem.

Peter

1999\01\12@184531 by Mike Morrin

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At 10:30 pm 1/12/99 +0000, Peter L. Peres wrote:
>Hello,
>
>  I know that this method seems funny (and Alice needled me) so I'm
>looking at the various problems: Turns out that no-one ever heard of pipe
>organs de-tuning themselves, that the resonant frequency is linearly
>proportional with the column height (strictly linearly)

No, it is the resonant wavelength that is directly proportional to length
(does the frquency get bigger or smaller when the length gets bigger?).

The relationship between wavelength and frequency does IIRC depend on
atmospheric pressure.

regards,

Mike

1999\01\12@212540 by James Cameron

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Mike Morrin wrote:
> (does the frequency get bigger or smaller when the length gets
> bigger?).

Smaller.  Larger organ pipes are lower frequency.  There are all sorts
of standing wave tricks as well according to how the pipe opens at the
end, if indeed it is open.  To remember, think of a piccolo versus a
flute.

I did physics of music for a year or so way back when.

--
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1999\01\13@061406 by paulb

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Peter L. Peres wrote:

> Turns out that no-one ever heard of pipe organs de-tuning themselves,

 !!!

> that the resonant frequency is linearly proportional with the column
> height (strictly linearly) and that very small length changes give
> small but very constant frequency changes.

 Resonant frequency is (fairly) strictly *inversely* proportional to
column height (from throat to opening).

> Atmospheric pressure and temperature do not play a role as far as pipe
> organ experts know.  So it should work even over changing temperature.

 Well, I can only say, whoever your reference board of "experts" are,
they have presumably not *actually* maintained a pipe organ.

 *Alternate* explanation:  They are tone deaf.

 Pipe organs, (like virtually *all* non-electronic, by which one
generally means quartz-locked, instruments), require moderately regular
tuning and our organist is quite adamant that the swell gate *must* be
left open every time the organ is shut down to maintain thermal
equilibrium ready for playing the next time.

 It matters less that the pitch of the whole organ drifts uniformly
with temperature in the loft, which I hardly need point out can easily
vary by 30¡C or more in this *temperate* climate.  If one part,
particularly the swell box which is *insulated*, is at a different
temperature the character (beats) of the machine can get quite odd!

 I think you'd better do a *lot* of homework on this one, Peter!  The
question you are addressing is: "Does the speed of sound vary with
temperature and pressure?"
--
 Cheers,
       Paul B.

1999\01\13@121648 by Peter L. Peres

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Hello Mike,

On Wed, 13 Jan 1999, Mike Morrin wrote:

{Quote hidden}

Right. The length is inversely proportional with the frequency.

> The relationship between wavelength and frequency does IIRC depend on
> atmospheric pressure.

Yes but musicians who play organs don't care about 'lows' and 'highs' on
the barometer and they have the equipment to hear 2 Hz differences and
much less sometimes.

Peter

1999\01\13@121658 by Peter L. Peres

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Hello Paul,

On Wed, 13 Jan 1999, Paul B. Webster VK2BZC wrote:

{Quote hidden}

That is what I meant. I meant to say that it depends only on length,
temperature and pressure, linearily (inversely proportional, to be exact
?). I think that I sometimes make bad choices for my English
words/phrases...

{Quote hidden}

What has the swell gate got to do with 1 lone pipe ? BTW musicians DO hear
2 Hz 'off' without a reference to compare with. This is a fact afaik.

>   It matters less that the pitch of the whole organ drifts uniformly
> with temperature in the loft, which I hardly need point out can easily
> vary by 30°C or more in this *temperate* climate.  If one part,
> particularly the swell box which is *insulated*, is at a different
> temperature the character (beats) of the machine can get quite odd!

This is correct, but 1 lone pipe beats only against itself ;). A 30 degree
C temperature change should cause a frequency shift of at most 3% or so.
Thus a thermistor...

Of course one has to do the whole sensitivity calculus for this for a
serious application.

>   I think you'd better do a *lot* of homework on this one, Peter!  The
> question you are addressing is: "Does the speed of sound vary with
> temperature and pressure?"

Come on Paul. When I was a kid I spent a lot of time in a real church with
a real big organ while a friend practiced his talents on the instrument.
Plus the "instrument" I was talking about here does work.

Peter

1999\01\13@125754 by Mike Morrin

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At 02:16 am 1/13/99 +0000, James Cameron wrote:
>Mike Morrin wrote:
>> (does the frequency get bigger or smaller when the length gets
>> bigger?).
>
>Smaller.  Larger organ pipes are lower frequency.  There are all sorts
>of standing wave tricks as well according to how the pipe opens at the
>end, if indeed it is open.  To remember, think of a piccolo versus a
>flute.
>
>I did physics of music for a year or so way back when.


so if you have a linear function which has a negative slope, increase the
length enough, and you will get a negative frequency.

 ^
f|
 |\
 | \
 |  \
 |   \
 |____\____________>
       \          L
        \

I suggest therefore, that it is not a linear function.

regards,

Mike

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