Sound board trenching and stuff

[Overs Pianos]

>Ron,
>
>What does the trench do again?   I'm trying to figure out what a 
>extreme thinning of the board in a small area does?
>
>
>David Ilvedson, RPT
>Pacifica, California

Hi David,

The trench is positioned just out from the inner rim joint with the 
sound board panel, and  positioned around the proximity of the lowest 
bass note, A1. The idea is to allow the diaphragm maximum perimeter 
flexibility where its most needed. The lowest note at 27.5 cps 
requires the board to be quite mobile, if it is to produce good 
fundamental tone. There is much debate as to whether the fundamental 
can be heard at A1, but nevertheless, the effect of trenching is 
significant. If it is continued too far up the scale there is a risk 
of creating a boomy undesirable tone for the higher notes on the bass 
bridge.

This piano in particular (KG6) wasn't the best laid out in the world, 
with respect to the bridge placement. The low bass bridge is really 
too close to the low end of the long bridge. I have therefore kept 
the trenching a little short on the left side of A1, but it would be 
unwise to take it any further around towards the long side, because 
it would allow too much board flexibility at the low end of the long 
bridge. If money and time was no object, this piano could do with a 
new plate to move the bass bridge at A1 about 4" (100 mm) further 
away from the long side. The KG5 is a much better design.

There's so much waiting to be discovered with new design. Its an 
exciting time be here.

Ron O.

-- 
OVERS PIANOS - SYDNEY
    Grand Piano Manufacturers
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Web http://overspianos.com.au
mailto:ron@overspianos.com.au
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