Let me restate the question

[Delwin D Fandrich]

| -----Original Message-----
| From: pianotech-bounces@ptg.org 
| [mailto:pianotech-bounces@ptg.org] On Behalf Of Overs Pianos
| Sent: February 06, 2006 11:01 AM
| To: Pianotech List
| Subject: Re: Let me restate the question
| 
| ....
| 
| One of the principal structural benefits of the ribs is that 
| it gives the overall assembly a sufficient sectional depth 
| that the panel and ribs can, together as a unit, provide the 
| necessary stiffness.
| 
| I'm not suggesting that a laminated panel wouldn't have a 
| higher stiffness than an equivalent thickness solid panel. It 
| certainly would, but not enough to support downbearing in its 
| own right. If you find this hard to believe just laminate a 
| little section for you own investigation.
| 
| Best,
| Ron O.



With respect, Ron, I do find your argument hard to believe because I have
thought this through, done it and it works. 

Keep in mind that one of the principle benefits to using something like a
laminated panel is that you can spread your anticipated load over a much wider
area.

And, just how much string downforce are we anticipating here? In a typical,
real-world piano this might average around 1/2 of 1% of the string tension.
Assuming three strings per unison, all at 175 lbs, this gives a total unison
string tension of 525 lbs. (It's going to be less than this where the scale
calls for mono-chords or bi-chords.) This means there will typically be a little
more than 2 1/2 lbs of string downforce per unison. Assuming 88 unisons in the
scale this will give a total string downforce load of about 300 lbs. Even if you
try for a total string downforce of 1% the total load is only going to be around
600 lbs. And that for only the first year or so of the soundboard's life.

Now, keeping in mind that this load is going to be distributed over most of the
whole surface of the soundboard panel, a lot of this load is going to be applied
up in the high tenor and treble sections where the bridge is not going to be all
that far from either the rim or the bellyrail. In other words, the span will be
quite short and easily supported by even a relatively thin laminated panel. The
only area where the span will be very long will be in the low tenor and bass
region where, for the sake of argument, let's assume that about half of the
string downforce -- let's say 150 to 300 lbs -- might have to be supported.
Probably less, since many builders back off on the string deflection angles
through the low tenor and low bass regions. And, remembering that unison tension
won't be as high with the mono-chord and bi-chord unisons. It really doesn't
take much of a laminated panel to accomplish this. Especially considering that
the length of the span won't be much over 1 meter (39.4" or so).

Del

Del