seating/False beats - a correction

[Jim]

Hi Ron:

This makes more sense than anything I have seen to date.  If true, it
could be measured with a depth gauge in summer and winter to verify.

Jim Coleman, Sr.


On Mon, 14 Apr 1997, Ron Nossaman wrote:

> Interested participants,
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> I'd have to go with Bob Davis and Jim Coleman Sr. on this one.=20
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> Further thoughts: Playing with my third tuning today (K.Kawai grand), I w=
as dinking around with the false beats I was getting in octave 6. ALL of th=
e beating strings cleared up with a slight pressure on the side of the brid=
ge pin opposite the string. Gotta be loose pins. Light seating helped on SO=
ME of the beaters, not all. Probably floaters, got them down where the hori=
zontal scrub on the bridge overcame pin flex. While playing with this, I th=
ought of another possibility as to how strings get up on bridge pins.=20
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> When a pin is originally driven into the bridge, the part of the hole tha=
t has had the least amount of pin pushed through it is the very bottom. Sin=
ce the bottom of the hole experienced the least wear and trauma with pin in=
sertion, it ought to have the tightest grip on the pin, with the loosest fi=
t occurring at the top, or entry point. The piano is strung and the strings=
 are seated on the bridge. With high summer humidity, the bridge swells. It=
 grows taller, the pin does not! The pin, gripped most firmly at the bottom=
, has the top of the bridge literally sliding up it, taking the string with=
 it. Since the extreme side bearing of the string on the pin puts the net (=
side&down) bearing angle at something near horizontal and probably not far =
from 20 degrees from PERPENDICULAR (thanks Mike) to the pin, when the bridg=
e dries and shrinks, the string stays up. Meanwhile, the extreme sidebearin=
g makes the string very hard to push up the pin and mashes a GROOVE in the =
top of the bridge. This movement also saws the bridge pin against the top o=
f the hole, at a side pressure somewhat less then the string  sidebearing f=
orce (minus spring of pin), with each cycle. No wonder the holes oval out a=
nd the pins get loose at the top! If the strings are tapped down when they =
are noisiest ( Winter, pianos get really clear and sweet when the humidity'=
s high and don't need it ), the bridge top will again be more deeply groove=
d with the next high humidity cycle. Even if they are tapped down as gently=
 as possible, they will damage the bridge on the next cycle! Epoxying the b=
ridge pins in solidifies the column of wood immediately around the pin and =
severely limits it's vertical movement, relative to the pin, with humidity =
changes. If this is a good model, the tapping isn't what does the damage, i=
t just makes it possible for the bridge to crush itself. I like this explan=
ation. I think it's logical and simple  - Ocham's Razor -. The simplest exp=
lanation is probably the correct one. What do you think?
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> With some trepidation,     Ron (simple, ask anyone) Nossaman
>  =20
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> At 03:26 AM 4/14/97 -0400, you wrote:
> >> If there are false beats, then the vertical component of the string
> >vibration
> >>  would have to vary cyclically.=20
> >> Bob Scott
> >
> > Only if you explain false beats as amplitude modulation. Frequency
> >modulation makes more sense to me, as explained by Jim Coleman Sr.
> >(difference in speaking lengths in vertical and horizontal modes causes =
pitch
> >change. This can be due to unclean notch OR bridge pin which wobbles in
> >horizontal mode, causing the string to act longer in that mode).
> >
> >Bob Davis
> >
> >
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>  Ron Nossaman
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