Sound-board modification

[Delwin D Fandrich]

Andrew,

Have you ever been to one of my (many) classes and/or seminars on the subject?
This stuff is covered in some detail. Including at least an overview of the
technical knowledge that is helpful in making such decisions. 

We "float" soundboards quite a lot, especially in smaller pianos, but there are
some other things done that lead up to the float. Floating an existing
soundboard without making some other modifications might help some specific
tonal problems (though not this one) but it can also cause some problems.

The tonal problem you are describing will probably not be helped by floating the
soundboard anywhere. This is usually done to free the very low bass. Done wrong
it may well make your problem worse. What you describe sounds more like a
classic case of the "end-of-bridge-effect." The cause for which, and some
potential solutions, are also presented. Briefly, the low tenor area of the
bridge losses quite a bit of stiffness and mass as you approach the end of the
bridge. The piano is not a uni-chord, and the strings of a specific unison do
not move just that portion of the bridge/soundboard system to which they are
attached. They move the whole bridge through some considerable distance on
either side of the point at which they are attached. And then you get to the end
of the bridge where the strings work against an increasingly flexible
termination. The result is a loud, boomy sound much like you describe. 

No amount of soundboard float is going to help that. You can alleviate at least
the missing mass part of the problem by attaching weights to the bottom of the
soundboard. And, in some cases, you can improve the low stiffness problem by
attaching various wood plates underneath the soundboard in the region of the end
of the bridge. (These are all patches to an existing poor design. If you are
actually replacing the soundboard and bridge system there are other much more
elegant solutions available.)

But, as I said at the beginning, all of this information is presented in the
seminars I do on the subject. It's a good way to get started. You can, of
course, do all of the experimental work yourself but you will probably save a
lot of time and frustration to find out which mistakes others have made before
you make the same ones yourself.

Del 

| -----Original Message-----
| From: pianotech-bounces@ptg.org 
| [mailto:pianotech-bounces@ptg.org] On Behalf Of Andrew and 
| Rebeca Anderson
| Sent: December 21, 2005 12:31 PM
| To: Pianotech
| Subject: Sound-board modification
| 
| That little (5') baby grand with the now tamed board in it 
| has another issue.  The tenor is nice and big, even boomy at 
| the end of the long bridge.  Then you cross the break and 
| there is a significant drop in volume.  The volume then 
| increases till we get to the bottom of the bass bridge where 
| it is powerful again.  The upper end of the bass bridge is 
| quite close to the rim.
| 
| This question is for the re-builders.  I'm thinking of an 
| unobtrusive design modification to the sound-board under the 
| plate. ;-) I own 
| this one outright, so....	How risky is it to zip a cut in the 
| sound-board along the rim around the upper end of the bass 
| bridge?  I'm guessing to start short, like three inches and 
| grow it a little as testing may indicate.  Would it be 
| preferable to tame the bottom end of the long bridge?  Would 
| a sort of "rib" glued up with ends glued and screwed to the 
| rim work like a cut-off to tame that end of the bridge and 
| unify things be better than loosening the sound-board?
| 
| With fingers itching and tools gleaming, Andrew Anderson
| 
| _______________________________________________
| pianotech list info: https://www.moypiano.com/resources/#archives
|