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I will put this on my to do list, unless someone has already done it or beats me to it.

Best regards-

Enter the radius crowned soundboard:
Glue up to ribs around 6 to 6.5% moisture content so there is very little compression in the panel. No need to dry the panel down to 4% or less then subject the panel to excessive tension and compression.
Ribs are cut so that the apex of the crown is mostly directly under the bridge except in the lowest bass and treble, where on compression panels the crown happens somewhere on the board and you live with it.
The amount of crown is designed into the radius that is cut onto the ribs and graduates smoothly and evenly across the entire panel. (I like to believe that this makes setting bearing and bridge carving a bit easier)
The ribs are designed to support string down bearing (as a structural member) and they do not resist crown as in a compression board with flat ribs.
String down bearing can be designed so that it is never greater than the amount of available crown.
It is a controllable system with some aspects that are predictable.

Thanks Gene, you added one of the methods.

AS I have seen it pictured the ribs are shaped and can be shaped so the apex is on the 1/3 of the front rail so the bridge is also providing some stiffening and the amount of stress provided to the board is progressly higher when coming to the treble.

That seem to induce much computation to design the ribs and the cauls.

That method put the higher spot of the bridge on the front of the bridge in the 5-6 octave region.

About your drying level, really compression is said to help the panel accept high level of dryness later. and is not necessarily used on flat ribs.

Now probably the more desequilibrium can be entered (within limits) in the panel, the more reactive it must be, (but also the more stress, the best the treble crispness, unless the piano is relatively small)

The amount of control on shape and resiliency is just amazing when you see it.

Then , all computations are said to give results at 20% approx.

DO you use a caul with extra curve or just fitting the final shape , with the method you describe ?

That thread is interesting

The descriptions given state about the 4 methods - 2 with more control on final shape - 2 with more resistance to cracks. (to simplify)

Best regards

14mm may be a measuring error, but not by too much. We do tend to bend a rib to test its tolerance. and this is the longest rib of a yacht tail 109-c chickering at 1280mm.

A 1200mm wide section will shrink between 6 and 8 mm when dried.

the 20mm measurement was the difference between the original size of the panel and its stable adjusted size after all accumulated shrinkage is released through the ungluing.

That seem to induce much computation to design the ribs and the cauls.
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The actual calculations take less than an hour using spreadsheet.

I can imagine that the usual method to compute ribs for an existing panel shape is not that complicated. I talk of something that push the resonant frequencies of the soprano enough on inner stress basis.

The web numbers that are produced could certainly be with a good spreadsheet, but due to the progressive curves the spreadsheet may not be that easy to setup. 4 different radii for each rib seem to complicate the computation enough .

Last new board I tuned had a basic and limited treble with no elegance, like with feet in the mud... (on a Steinway) Basses and mediums are easy probably and may be high treble as well, but on the 5th rib region seem to occur a hit or miss game.

20 mm , once the ribs are unglued ! I have seen some horror movies that where less bad !!

Could someone explain that to me ?
As I see it, the underside of the panel is compressed (tensed) at the time of ribbing, if curved cauls are used on a yet dryed panel.

Then when moisture get back, it is retained from expanding but not compressed more (there is indeed some form of compression due to the fact that the wood is not allowed to get to its previous condition, but the drying is there to protect it somehow, giving the wood some resiliency "reserve".

It is said that a lightly dried panel is more prone to develop cracks .

Why wanting to leave the board in an uncompressed condition ?

DO have it right ?

Is the "position" of the neutral fiber in the panel computed, or envisaged, or is it too idealistic to try to get it under control ?

A Steingraeber from 1909, with unusual SB grain almost parallel to belly rail... with very long and high ribs disposed longitudinally to the piano length... The panel has less than 7mm thick, has not cracks and perfect downbearing from beginning... I am asking if this way provides more rigidity to the system, at cost to the final sound... (pending to finishing and hearing it).

My guess is that the bass and lo-tenor sections are a bit too stiff making it difficult to get a clear defined tone with good fundamental and the treble may not be stiff enough.

Soft tone, with no much high frequencies for the ones I have seen.

But they had many cracks, always

Hi Isaac. According Steingraeber this pictured model is the improved version (30 years later) of the famous last piano Liszt. There are many recordings of this grand (which of course was full restored but maintaining original SB), for instance http://www.youtube.com/watch?v=UV1lmRb4_Gs
It doesn't seem to me precisely a soft tone.

Hello, thank you so much for the recording.
I recognize the characteristic by a relatively fast absorption of energy with no much high partials provided.


Seem to me the panel is not resilient much.
I have a vertical piano with similar setup, and similar round tone but with limited dynamics .

It may be what was called "light panel" construction, while more actual ones range from 6-7 to 9-10 mm.

Well, personally never heard a 130 years old modest (200 cms) grand piano with this full/complex tone and this great dynamics.
Steingraeber did the things well...

Yes it is juicy, (200 cm is yet full scale or near, BTW).

What I hear is the tone circulation is not very long.

The piano do not saturate easily, on the other hand.

I like that sort of tone, my comments was about real thickness and dynamic plague if compared with more massive/resilient soundboard.

Great way to state it, Mr. Oleg.

After looking at the numbers thought, I am in full agreement. There is absolutely huge in-plane compressive stress in the soundboard as it wants to expand with humidity when constrained by the ribs and the rim. It is easy to see that Mr. Ialeggio is correct about the frequent existence of yielded wood in the soundboard.

Maybe the following that I am seeing is obvious to some and not to others --
Both modulus of elasticity and yield stress in compression varies with orientation of the grain. For both these figures, the difference is almost an order of magnitude as you move from radial (quarter) sawn to the situation with the grain running in plane with the width of the board (laterally). Expansion with humidity also varies with direction of grain. So, the angle of the grain in the soundboard would make a huge difference in the final mechanical properties of the board. Fortunately, the data for all this seems to exist for Sitka spruce, though there is variability in the figures among the references - makes sense, it is a natural material.

I'm supposing Mr. McMorrow is correct, that some of the stress in the board coming from humidity has to be relieved in bowing in the board (the stress levels would certainly be worst than a horror movie, without something giving). We all know the board gives to an extent, but it would be interesting to quantify this effect.

That is where I am at in my discovery. I will look further and report, but no promises for timeline.

Regards -

Boards are clearly "supposed" to be made from quarter sawn.

hey probably are not depending of the quality...

The amount of compression installed at ribbing is what allow the board to accept future humidity fluctuations.
It is supposed to stay within limits of acceptability, a less dried panel would develop ridges (often seen on modern pianos and absent from older ones)

This is backwards. It is the boards that are dried to the edge cell damage that will be pushed over that damage threshold during moisture cycling. Compression ridges do not occur on boards installed at 5.5% or higher. These higher-emc-at-ribbing boards are far enough away from the compression failure threshold that there is more resilience in both the joint and in the wood throughout the field.

Jim Ialeggio

Well I did not make panels, so I have to trust you but if the wood is constrained at ribbing time it will be happy to receive some moisture, and the compression will be less strong than when it is dry.

The ridges I notice on some modern panels at joints are not there on old boards.
It seem evident that the wood have been pushing where no contraction reserve exists and a ridge develop.

I did not notice them on old soundboards (the panel surface is flat without those hops)

Certainly a wood with damaged cells will not keep enough elasticity to follow when the moisture is high, it may happen, but at last it is less sensitive to high level of dryness.

The goal clearly stated anyway is to have a soundboard that contains enough inner stress to accept moisture fluctuations without cracks. "the board is kept in is constrained state for the time of its useful life" (Bluethner, Fenner, U.Laible).

Now I understand that under heavy climatic conditions, the soundboard builder will err on the side of caution, and will make panels that are made more neutral ? Then I was surprised to read that the protective effect against cracks is due to the compression/drying, but I did not invent it.

If not for that, just to raise the treble frequencies, so the treble part of the piano have that shiny quality, and not that tendency to produce more low pitched treble I seem to notice on a few boards I heard.
(together with a "slow" reaction time, seem to me.)

Now I suppose there is the panel of the piano technician, and the one that can be made in a factory with adequate control on drying of all elements (while this does not seem to be so complicated to attain for the equiped tech, while precise wood moisture room may mean a strong deshumidifier, if not heated box.

The ribs seem to be dried more than the panel , the bridge also is dried.

Now I have seen a pneumatic press used with some sort of moistening of the surface of the panel (unless it was a product intended to harden the wood surface before the lacquering) . and I have no real explanation on that, possibly only for the bridge gluing with a certain method.

Hello soundboard makers,

What kind of angles (typical and maximum) in the grain are you seeking when you take apart an old soundboard and look at the individual board at the end grain at the board end? How true to quarter-sawn wood are other people using in medium to high quality boards? (I don't ask about you, because of course you are top class, a special case!)

As a coordinate system, assume 0° is approximately ideal quarter sawn wood, like in the blue box here:
http://upload.wikimedia.org/wikipedia/commons/4/45/Softwood_endgrain_marked.png

With this, I would like to make a spreadsheet for the stress state in the board and how it varies with subsequent humidity changes.

Kind regard-