Recrowning/bridge wedging

[Ron Nossaman]

Rim spread isn't the only, or probably even the most likely, reason for a=
 soundboard to flatten. How's that for a totally un-provable statement? The=
 pianos with flat boards that have been around from the 1920's and before=
 have lived through miserably inadequate climate control through most of=
 their lives. Through most of that time, few homes (and virtually NO=
 institutions) had provision for cooling and dehumidifying in the summer,=
 and heating with humidification in the winter. Those compression ridges you=
 see on brand new grand soundboards are the indication that the wood is=
 working a lot closer to failure limit than you would like to see in a=
 footbridge you have to walk across. It's necessary for tone production, but=
 not optimal for durability. Doing that pitch raise in the winter puts more=
 load on the board with the humidity upswing and crushes the cellular=
 structure of the board. The wider the humidity swings, the faster the=
 deterioration. Not doing low humidity tunings might prolong soundboard life=
 (another un-provable), but isn't an option in the real world. With the=
 passing years, the reaction of the board to humidity swings lessens, as the=
 percentage of crushed cells in the board increases, until the board is=
 flat. Excessive downbearing will accelerate this process. If, as (I think)=
 Chris Robinson suggested, the initial bearing is established so a flat=
 board equals zero bearing, you have an optimal system where bearing force=
 diminishes proportionally with crown and doesn't abuse the board. In other=
 words, bearing should be a function of crown, not something the=
 manufacturer establishes arbitrarily.=20


I can't see this bridge kerfing/wedging thing working either. The bridge is=
 just what it's called. It's a bridge, intended to convey something from one=
 end to the other. It's purpose is to distribute vibration across the=
 soundboard. Even if putting a wedge (or twelve) in it didn't adversely=
 affect this vibration propagation, it's still not addressing the cause of=
 the problem. The sound is amplified by the soundboard, it's a SOUNDBOARD,=
 not an awning. Hanging a flaccid soundboard on a wedged up bridge isn't=
 going to cure anything. The bridge, in it's ORIGINAL configuration worked=
 just fine with a VIABLE soundboard. Touching up the X-rays won't cure the=
 illness.=20

PS: The hardest part of any fix is an accurate diagnosis. My opinion.


I hope this makes sense and isn't just random blithering from an old=
 curmudgeon.






At 06:42 PM 5/30/97 +0000, you wrote:
>> Date:          Fri, 30 May 1997 08:14:24 -0700
>> From:          Tom Myler <TomMyler@worldnet.att.net>
>> Subject:       Re: Recrowning
>> To:            pianotech@byu.edu
>> Reply-to:      pianotech@byu.edu
>
>
>My experience with older Mason & Hamlins is I often find the=20
>boards flat.  I thought the resonator might have something to do=20
>with flattening the board?...
>
>ilvey
>Pacifica, CA
>


 Ron Nossaman