Sound waves(The behavior of soundboards)

[Delwin D Fandrich]

----- Original Message -----
From: "Phillip L Ford" <fordpiano@lycos.com>
To: <pianotech@ptg.org>
Sent: January 13, 2002 2:35 AM
Subject: Re: Sound waves(The behavior of soundboards)


> >     For example, athough I think it likely the bridge motion proponents
will
> >contest this, and I await the next ingenious denial, their ideas would
suggest that
> >the agraffe itself must be moving similarly to the bridge, although on an
obviously
> >reduced scale- that is rocking fore and aft, flexing side to side and
moving the
> >plate underneath it.  I rather doubt it.
>
> No I don't contest or deny it.  This is consistent with the idea of force
being
> applied by
> the string to its supports as it vibrates.  If a force is applied, unless
the agraffe
> and plate are infinitely stiff then they must move.  This seems consistent
with
> what the designers try to do - make the agraffe and plate system very
stiff here
> so that they move as little as possible so that string energy is
dissipated as little
> as possible at this point.  This would certainly be easy enough to prove
or
> disprove.
> Simply put an accelerometer on an agraffe and strike the string.  If you
are correct
> then the accelerometer would register zero.  In my opinion, if this were
to happen,
> it would be in your words 'fantastic'.

Phil, this is precisely what does happen and, yes, it is proven by the
accelerometer tests you've described. The agraffe does move in response to
the motion of the string. As does the capo tastro bar. Hence the various
schemes to couple the capo tastro bar to the pinblock flange.

Del


>
> > Similarly, the rear duplex, where sound
> >can be heard by examining the string with the stethoscope, should cause
the hitch
> >pin to be subject to a similar effect.  Yet, when one listens with the
stethoscope
> >to the neighboring string very little sound is heard.  This occurs as the
stresses
> >in the wire rounding  the pin becomes so great  relative to the stresses
that are
> >the propagating sound in the wire that they are unable to propagate
coherently
> >through the more intense stress concentration rounding the pin.
>
>
> >Regards, Robin Hufford
> >
>
> That's your explanation.  Mine would be that the speaking length is
vibrating, which
> moves the bridge, which causes the backscale to vibrate.  Most of this
vibration is
> reflected at the duplex bar so very little makes it through to the short
length of
> string between duplex and hitch.  Since this portion of the string is not
vibrating
> there is no oscillating or vibratory force applied to the hitch pin.  What
the hitch
> pin essentially sees is the static load from the string.  So it doesn't
surprise me
> that there isn't much vibration in the area of the hitch pin.

Plate flanges also move in response to the vibrating energy in the strings.
It also is proven by the various accelerometer tests that have been
conducted over the years. This motion is the basis for the Steinway bell and
coupling bolt along with the various nosebolt schemes that have been
developed over the years.

Del