The Richard Gertz myth

[Overs Pianos]

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All,

Back in 1900, if the patents-office examiner had been paying 
attention, Richard Gertz never would have got his patent. The sound 
board of a real world piano does not push outward as downbearing is 
applied. While the sound board shown in the piano diagram at Mason 
and Hamlin's website (http://www.masonhamlin.com/crown/crown.html) 
might push outwards, real pianos do not have the sound board ribs 
offset higher than the cord-line as shown in their image (a jpeg 
conversion of the M&H website image is shown below). Notice that the 
M&H drawing shows both the ribs and sound board panel above the line 
in this exaggerated drawing. In reality the ribs are way below the 
line.


jpeg image converted from gif at - http://www.masonhamlin.com/crown/crown.html


When Ron Nossaman was here in July, he mentioned that sound boards 
pull in when the down bearing pressure is applied.  While a crowned 
sound board, if it had no ribs, would push out, the ribs are much 
further below the cord-line than the sound board panel is above it. 
So the net result is that the sound board will PULL IN.

Yesterday I proved this to my satisfaction. I built and load tested a 
model of rib 6 (numbered from the back) for a Steinway D, attached to 
a 142 wide strip of 8mm thick Sitka spruce panel. This rib is 990 mm 
long overall (65 mm shorter than standard on account of the sound 
board cut-off), with an inner rim contact of 40 mm on the treble-bent 
side, and 30 mm on the new sound board cut-off. At 0.75 degrees of 
downbearing angle (a typical figure over this rib on a D), there will 
be 10.6 Kg down bearing from the treble bridge and 6.4 Kg from the 
bass. When we applied this load to the sound board test strip, with 
one end of the strip clamped to the bench and the other end free, it 
caused the free end to pull in 0.05 mm (2 thou).

So yes, a substantial back beam configuration is a good thing, but 
the Richard Gertz 'crown retention system' will be of virtually zero 
assistance.

Ron O.

PS. Some of you may be asking, 'is he still building that Steinway D 
board'? The answer is yes. We completed the 'new sound board' job a 
couple of weeks ago. However, I didn't like to tone it produced, so 
we removed the sound board again last week to redo it. The 
re-configured panel is assembled and tapered and I expect to have the 
I-rbs together by the end of today. I will discuss the whys and 
wherefores about this project once I get the piano up and running.
-- 
OVERS PIANOS - SYDNEY
    Grand Piano Manufacturers
_______________________

Web http://overspianos.com.au
mailto:info@overspianos.com.au
_______________________
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