seating/False beats - a correction

[Ron Nossaman]

Interested participants,

I'd have to go with Bob Davis and Jim Coleman Sr. on this one.=20

Further thoughts: Playing with my third tuning today (K.Kawai grand), I was=
 dinking around with the false beats I was getting in octave 6. ALL of the=
 beating strings cleared up with a slight pressure on the side of the bridge=
 pin opposite the string. Gotta be loose pins. Light seating helped on SOME=
 of the beaters, not all. Probably floaters, got them down where the=
 horizontal scrub on the bridge overcame pin flex. While playing with this,=
 I thought of another possibility as to how strings get up on bridge pins.=
=20

When a pin is originally driven into the bridge, the part of the hole that=
 has had the least amount of pin pushed through it is the very bottom. Since=
 the bottom of the hole experienced the least wear and trauma with pin=
 insertion, it ought to have the tightest grip on the pin, with the loosest=
 fit 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 bridge dries and shrinks, the string stays up. Meanwhile, the=
 extreme sidebearing 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 of the hole, at a side pressure somewhat less=
 then the string  sidebearing force (minus spring of pin), with each cycle.=
 No wonder the holes oval out and 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 grooved 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 bridge 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, it just makes it possible=
 for the bridge to crush itself. I like this explanation. I think it's=
 logical and simple  - Ocham's Razor -. The simplest explanation is probably=
 the correct one. What do you think?

With some trepidation,     Ron (simple, ask anyone) Nossaman
 =20



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
>
>

 Ron Nossaman