ETD question re: unisons

[Tom Cole]

Carl,

I seem to remember, from a class on the Wapin bridge, that the cant of
the front bridge pin causes the vibrating motion to precess from
vertical to horizontal, etc., and that the vertical pin on a Wapin
bridge allows for circular motion almost immediately.

I don't know if this helps you any but I thought it might bear on your
question in some way.

Tom Cole

Meyer Carl wrote:
> 
> Hello Mr. Curious:  I am curious2.
> 
> Yes, I read that  and think that he really has a handle on the reason for
> prompt sound and aftersound.
> 
> I had a loose leaf notebook with a Xerox of that article along with articles
> by Jim Ellis, a couple of guys from Baldwin, both from the journal, and a
> comment from Ed McMurrow about horizontal vibration of strings from his book
> "The educated Piano".  I must have loaned it out since I can't seem to find
> it.
> 
> As I understand it, a string will vibrate vertically (grand piano) and the
> impedance of the bridge will be low, hence dissipating energy at a fast
> rate.  Then due to imperfections the strings vibrations will slowly change
> to elliptical and then progress to horizontal.  At the horizontal mode the
> impedance of the bridge will be much higher resulting in a slower rate of
> dissipation.  This is easily understood by comparing a capacitor in an
> electronic circuit, discharging into two different resistive loads.
> 
> In the case of the piano, the two different loads are not switched abruptly,
> but gradually.
> 
> One statement I read was that good pianos don't have horizontal vibrations.
> Really?
> I guess that if the strings were perfectly leveled, the hammer perfectly
> mated to the strings, then the horizontal vibration would be minimized or
> maybe delayed.
> 
> Now my question would be.  If that were true would the shape or point of
> shift in the amplitude plot be delayed?  That would be an interesting
> question to test with a set up to plot the timing of the transition from
> prompt sound to aftersound with different string levels etc.
> 
> Anybody care to render an opinion?
> 
> Carl Meyer
> 
> ----- Original Message -----
> From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
> To: <pianotech@ptg.org>
> Sent: Thursday, February 15, 2001 9:04 AM
> Subject: Re: ETD question re: unisons
> 
> > I am curious.... just how many of you have read Gabriel Weinreichs paper
> "The
> > coupled motion of piano strings" ?
> >
> >
> > --
> > Richard Brekne
> > RPT, N.P.T.F.
> > Bergen, Norway
> > mailto:Richard.Brekne@grieg.uib.no
> >
> >
> >