Soundboard Installation & MC

[Delwin D Fandrich]

----- Original Message -----
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: <pianotech@ptg.org>
Sent: April 23, 2002 9:56 AM
Subject: Re: Soundboard Installation & MC


> Delwin D Fandrich wrote:
>
> >
> > > I suppose if you flat ribbed it and dried the bajeezers out of it, the
rim
> > just might help to hold a bit of crown - at least until it got off the
> > showroom floor!
> >
> > If the rim actually did support crown you'd never see a M&H with a flat
> > board!
>
> Why not let Mason and Hamlin speak for themselves on this matter ?
>
> http://www.masonhamlin.com/crown/crown.html
>
> The link above points to M&H 's current web page which I have to assume
reflects
> their current assesment of this subject matter. The page contains a nice
> explanation of their system and the reasoning behind it, good graphics
help to
> illustrate their point.
---------------------------------


Yes, Richard, I am familiar with this part of M&H's web site and I'm sure it
's a wonderful marketing tool. Unfortunately, as is often the case, there is
a gap between marketing claims and technical reality. Not even a nice
explanation and good graphics can overcome the inaccuracies of these claims
nor can they overcome known wood technology.

Among the technical problems I have with this site are .

1)  It is at least debatable that soundboard crown "increases the amount of
energy transferred from the piano strings through the bridge of the
soundboard."

2)  In explaining how much outward force is (potentially) generated as the
soundboard is loaded an assumption is apparently made that piano ribs are
made of a perfectly rigid material and that they flatten uniformly and
without distortion. They are not and they do not.

3)  The assumption is made that it is "the higher outward force [pushing]
the soundboard against the rim, compressing that side grain" that "causes
the soundboard to lose crown." Assuming that this condition has any effect
at all on the loss of soundboard crown, it is surely minimal.

4)  The second diagram implies that in its end-grain plane wood is "Not
Compressible." It is.

5)  It is implied that most pianos use a simple butt joint between the
bellyposts and the inner rim and, by implication, are inherently weak at
this point. In fact, most pianobuilders go well beyond that. S&S both
blind-dowels and overlaps these joints. Baldwin dowels them in a similar
manner. Others dovetail them. Still others run very long and very large wood
screws through the inner rim and well into the end of the bellypost. And
still others run very long dowels in through the inner rim and well into the
end of the bellypost. It is rare, in any reasonably well made piano, to find
a gap of any kind -- even one as small as 1/64" (0.4 mm) -- in these joints.

6)  It is claimed that "White spruce provides a higher strength per weight
ratio than the more widely used sitka spruce." According to the current
edition of the USDA Wood Handbook, Sitka spruce (at 12% MC) has a specific
gravity of 0.36 and a MOE of 9,900 MPa. White spruce (also at 12% MC) has a
specific gravity of 0.40 and a MOE of 9,200 MPa; Sitka spruce is both
lighter and stiffer than white spruce. Now, in fairness, these numbers are
quite close and in practical terms there won't be a lot of difference.
Still.

The list goes on, but these stand out.

Now, don't get me wrong. I think M&H pianos are good instruments. And they
are certainly built as well as most anything else out there today. But the
so-called Centripital Tension Resonator still does not support soundboard
crown or assure its longevity.

This whole argument rests on two assumptions:  (1)  Wood is not compressible
in its end-grain plane. But, of course, it is. Both under brief loadings if
the applied stress is high enough and under long-term loadings even at very
low stress levels. And, (2)  As string downforce is applied to the bridges
the ribs act as a true rigid (architectural) arch. They do not. Soundboard
ribs are made of wood, not concrete or stone. As such they have compliance
and they distort under the downward stress of the string downforce.

M&H piano soundboard assemblies will undoubtedly hold their crown for many
years. But it will be because they use a nicely radiused rib, not because of
the Centripital Tension Resonator in the belly.

Regards,

Del