Dear Mr. Skolnik,
I don't believe that all of the vibrational
energy is transferred to a lateral "push-pull" at the
level of the bridge cap. Just most of it. But that
holds intriguing implications for consideration,
regarding how bridge height affects leveraging the
vibrations into the soundboard, and what frequencies
might be augmented by various bridge heights and
thicknesses. Off hand, I would imagine that a low
bridge would favor high frequencies, and a high bridge
would favor low frequencies, as it would be out of
phase with rapid vibrations, due to inertial mass,
tending to mute them.
Hmmmmmmmmmmmmmm.
Thump
--- David Skolnik <davidskolnik@optonline.net> wrote:
> Beware Gordon!
>
> Are you prepared to re-enter the mine field? You
> are about to start
> talking about how the energy from the string
> actually becomes transformed
> into the transversal movement of the soundboard,
> required to create the
> sound waves we hear, forcing us to ask such
> questions like, for instance,
> do the strings make the bridge move up and down, or,
> for that matter, from
> front to back? If you choose to undertake such an
> adventure, you would be
> probably be well advised to avoid starting out with
> a virtual sign taped to
> your rear saying "KICK ME!" By that I am referring
> to your portrayal of
> the string pulling on the bridge cap. While I,
> personally have come to
> believe that the essence of your idea is correct,
> that is, all modes of
> string displacement being transformed into a kind of
> pulse energy at the
> termination, the string would, in no way, actually
> pull on the bridge cap,
> with the attending implication that the bridge is
> pulled forward and
> backwards, a motion you might more reasonably infer
> from a theoretical
> configuration which had the entire string terminate
> on the bridge, (Of
> course, in such an arrangement you would be
> dispensing with downbearing
> ...but...). If anything, it would be the pins that
> would be pulled, but,
> in that case, it would seem that the back scale
> would counteract any
> tendency to pull forward.
>
> I'm not sure what aspect of Bernhard Stopper's
> remarks you are reacting
> to. If anything, he seems to be saying, as are seem
> to be, that the bridge
> moves back and forth. I am doubting that such a
> description accurately
> reflects the mechanics involved, but that's only my
> gut speaking. I have
> to go back and read 5 Lectures again, along with the
> last 10 years of
> Journals and Pianotech.
>
> David Skolnik
>
>
>
> At 07:49 PM 2/11/2004 -0800, you wrote:
> >Excuse me, please, but is not the piano tone
> actually
> >caused by the tugging of the string on the bridge
> cap,
> >effectively making it a "bell crank"? Afer all, as
> a
> >string vibrates, the end pulls in and out, not up
> and
> >down. If it waved up and down, lifting and dropping
> >the bridge with it, the tone we hear would be the
> >frequency of the entire string--- from agraffe to
> >hitch pin. But it isn't.
> > Thump
> >--- Bernhard Stopper <b98tu@t-online.de> wrote:
> > > Dear Marc & Isaac,
> > >
> > > Longitudinal waves of strings produce
> transversal
> > > vibrations on the
> > > soundboard caused by the bridgeīs back and forth
> > > movement. If this would not
> > > be the case, one couldnīt measure or hear them.
> I
> > > think you donīt negociate
> > > that they exist, in the sound samples it is the
> > > whistle you can hear. As
> > > Isaac wrote, (he supposed it was the additional
> line
> > > below the 4.
> > > transversal but heard it an octave higher. It is
> > > overlaid with the 13.
> > > transveral, so that is indeed what you heard,
> (good
> > > ears Isaac, i am really
> > > impressed... )
> > >
> > > Measuring and separation of transverse and
> > > longitudinal harmonics were done
> > > with a software spectrum analyzer (spectraplus,
> you
> > > can download a test
> > > version at http://www.telebyte.com/pioneer/ ). A
> > > spectrum analyzer extracts
> > > every frequency that is in a sound wave over
> time,
> > > no matter if it is caused
> > > by a longitudinal or a transversal wave.
> > >
> > > To interpert the spectra, just "count" the
> regular
> > > lines.. there are 39
> > > transversal waves, and the first longitudinal
> wave
> > > (at about 712 Hz) is
> > > overlaid with the 13. transversal (a little
> thicker
> > > line) The various
> > > additional lines (mainly around the mid of the
> > > spectrum) are caused by the
> > > blank ends, the wave propagation is faster on
> that
> > > part of the string what
> > > results in splitting up several harmonics.
> > >
> > > to ask for a MiniMens Audio demo (the string
> > > simulator) and more information
> > > on the MiniMens program look here:
> > >
> > > http://www.piano-stopper.de/homepe.htm
> > >
> > > best regards,
> > >
> > > Bernhard Stopper
> > >
> > > ----- Original Message -----
> > > From: "Mark Kinsler" <kinsler33@hotmail.com>
> > > To: <pianotech@ptg.org>
> > > Sent: Wednesday, February 11, 2004 6:09 AM
> > > Subject: longitudinal waves
> > >
> > >
> > > > So there's a program that'll simulate the
> behavior
> > > of a stretched string,
> > > > non-linearities and all? I suppose I
> shouldn't be
> > > surprised, but I'm
> > > > certainly impressed. And the recording and
> > > simulation sounded alike
> > > (though
> > > > the attack, etc. was different.)
> > > >
> > > > I'm sitting here wondering how you could
> measure
> > > longitudinal waves on a
> > > > string separately from the transverse waves.
> It's
> > > easy enough to detect
> > > > motion in a plane perpendicular to the string,
> but
> > > how would you isolate
> > > > longitudinal waves?
> > > >
> > > > I wish those two spectra had some labels on
> them.
> > > I couldn't figure them
> > > > out.
> > > >
> > > >
> > > > M Kinsler
> > > > 512 E Mulberry St. Lancaster, Ohio USA 43130
> > > 740-687-6368
> > > > http://home.earthlink.net/~mkinsler1
> > > >
> > > >
>
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