"crown-forcing" springs

[Delwin D Fandrich]

----- Original Message -----
From: "Dave Nereson" <dnereson@dimensional.com>
To: <pianotech@ptg.org>
Sent: May 29, 2001 11:39 PM
Subject: "crown-forcing" springs


>  Regarding the use of auto valve springs to push up on a hardwood slat
across the ribs in an attempt to  force some crown into the board;  does it
have to be done across the whole soundboard, or can it be localized to one
area that doesn't have much volume (sustain is OK, but not great).

First, keep in mind that this is not an exact science. Very little
investigative work has gone into the best use of the technique.

Second, the idea is not really to force any crown into the board. True, the
board may well curve upward slightly with the addition of springs (and they
don't have to be 'valve springs') pressing up from below, but this is not
what we normally think of as soundboard crown. There will be some stiffness
added to the system, yes, but 'soundboard crown' will not change. Take the
springs away and the soundboard goes right back where it started.

Third, it can be localized if it is a localized problem you are trying to
alieviate. The most typical applications were through the killer octave
region and at the bass end of the tenor bridge.

Fourth, I'd be very surprised if any power was added at all. Sustain, yes,
but not power. Go back and read through the material in the pianotech
archives for more information.




>  The technician that demonstrated this at a chapter technical recommended
placing the slats across the ribs about a hand's width below the bridge (on
an upright, towards the bottom of the piano;  on a grand, towards the rim).
What's the reason for this? I would think applying the pressure toward the
middle of the board (above the bridge) would have a greater effect.  And why
not directly under the bridge?

I have no idea. The reason for doing this would probably best be explained
by the technician who domonstrated the technique to your chapter. Back when
I did what I did with this technique the springs went right under the
bridge. Or as close to it as possible.

Regards,

Del