[pianotech] Diaphragmizing

[Nick Gravagne]

Hello all,

There can be no clear recommendation either for or against diaphramizing a
soundboard either in whole or in part if we leave out the concomitant issues
of mass density, impedance, compliance and a host of other physical
phenomena such as spring constants and their relationships to potential and
kinetic energy, all of which cannot be discussed at length here. To most of
you bellyheads out there this is not news, of course.

For starters, Steinway's official designation since 1936 for Paul Bilhuber's
new idea is plainly called the "Diaphragmatic Soundboard" (DS) and it
differs from a simply thinned or diaphragmized board in that it is
constructed to have a "roundish" geographical center (9mm) from which a more
or less evenness of taper continues to the periphery (5mm), including the
belly rail. Many rebuilders have seen thinning patterns in old boards of any
manufacture, quite severe in some cases, which predate the DS by decades. 

I have in my shop a S&S L board from 1917 (I think) which is thinned to 5mm
from the tail all the way around the curve and up to and approaching the
highest treble note. The spine and belly edges are not thinned, but rather
equal the general thickness of the panel of about 9mm (a bit less at
0.350"). The area of thinning roughly follows the rib feathering lengths.
Thus, this L board is not technically a DS board. 

In 1935 and 36 Bilhuber and his partner C. A. Johnson of then E. E.
Laboratories conducted many scientific tests, particularly with regard to
"airborne" carrying power as compared to the non-DS boards of the day. They
claimed DS superiority.

There is no evidence I am aware of to suggest that highest lag bolt area
thinning was an expedient to allow head room for plate setting. Other posts
have suggested that bridge height and adequate downbearing can be
accomplished quite easily, not to mention that lag boss thicknesses and
manufactured rim elevations can be adjusted as well. 

More to follow, have to run.

Respectfully,

Nick Gravagne, RPT
Piano Technicians Guild
Member Society Manufacturing Engineers
Voice Mail 928-476-4143
 
-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of David Love
Sent: Sunday, January 25, 2009 9:28 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] Diaphragmizing

Many people do it and the practice has been Steinways for some time.  I'm
curious about when Steinway actually started the practice and since I
haven't taken out many Steinway soundboards that are newer I'm curious what
their current practice is and whether other makers historically have
employed this practice.  I always thin the boards I do in the bass section
graduating down to about 5 mm by the time one gets to the edge.  But farther
up on the bent side and in the treble I don't, neither at the belly rail.
While I understand the idea of creating greater flexibility in the bass
section for those low frequencies I'm wondering what the reasoning would be
for thinning higher up in the scale.  ...

David Love
www.davidlovepianos.com