Laminated Soundboard Ribs

[Phillip L Ford]

On Tue, 12 Feb 2002 16:42:18  
 Erwinspiano wrote:
>In a message dated 2/12/2002 11:52:14 AM Pacific Standard Time, 
>fordpiano@lycos.com writes:
>
>But, I do have a couple of possible complications to 
>the modulus of elasticity formulas and that is that the strength of woods 
>seem to vary between species and even in the same tree as you pointed out so 
>knowing how to select materials makes a huge difference when making 
>generalizations about the modulus of elasticity.  Still agood place to start. 

Agreed.  Like you say, a good place to start.  A lot of it seems to depend on
what woods are available and where they come from.  So rather than take
numbers from a chart I guess each maker would have to test a few sample
pieces of the woods that he's interested in and that are available from his
suppliers to settle on the type he wants to use.  Once that's done there's
still much selection that has to take place, as you say.

>      I was thinking about your comments about strength uniformity of 
>laminatd ribs and I believe this must be the major benifit. However I think 
>it's possible to get some semblance of or closer to  uniform results for rib 
>strength IF you can cut all your ribs from the same board. This is what I do 
>with the sugar pine ribs I use.  I select it myself looking for a nice tight 
>grain12 to 15 grains per inch. Just look at new Stwys the're still using flat 
>sawn sugar pine that must be 3 grains per inch.How strong can that be? Sugar 
>pine is extremely variable.

Also, using a laminated rib, I would think it would be easier to get truly vertical
grain material since the thicknesses of each lamination would be so much less
than with a solid rib.

>     As to the popularity of spruce ribs I think it is important to reiterate 
>my comments about how stiff is stiff enough in conjunction with what type of 
>soundboard material they're being glued to and at what grain angle.  All 
>these factors add stiffness.  I have used a variety of different types of 
>woods in different parts of the scale and have come some general tonal 
>conclusion  on sound and not necessarily the modulus of elasticity. At this 
>point in time with Sitka panels I like all tight grain sugar pine ribs or 
>sugar pine in the top and some species of spruce in the bottom. Why because I 
>like the sustain qualitys. I have a light but stiff rib glued to Sitka which 
>has a stiffer strength to weight ratio than other species of spruce So I 
>don't really need extra mass in the panel.  If I was going to use spruce in 
>the treble I believe wide grain sitka a better choice.

I was speaking only from a stiffness standpoint.  I would imagine that that is
not the only consideration (with regard to ribs) in the way the piano sounds.
This would get us back into the discussion of how the soundboard works and 
the influence of various rib parameters on that.  My understanding of that is
quite limited.  But it's not hard for me to imagine that some other rib parameters
than stiffness affect the tone and so some personal taste in the choice of materials
seems inevitable.

>It isn't just a glued up straight 
>beam it's a glued up curved beam. I believe in construction terms it would be 
>a prestressed beam or some such. This seems to me that it would make it 
>stiffer and more resistent to bending stress which would allow for a more 
>permanently  crown.

Good point.  I think you could be right about that.  This alone would make it
worth investigating further.

>    I wish we could have discussed all this stuff back when I knew 
>everything!
>

It wouldn't have done any good because back then I knew everything too, so there
couldn't have been a discussion.

Phil F


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