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Looking back in history I was never really able to determine who invented the compression soundboard.
Compression in the sense that the board is dried to a low EMC, glued in the piano so that a crown developed for added strength without adding weight.
Not really essential for harpsichords, fortepianos, or squares with the low tensions.
Using hygroscopic means to create a crown is just so clever, I always wondered who was the first to think of it.
Thanks

I don't know, but I think rib-crowning is even more clever.

Probably the first factory to use a kiln dryer. Chickering?

Would you be able to narrow that down to a certain year or so? And a person Jonah or one of his Sons (Frank?)
How certain are you they were the first with a Kiln?
Brilliant by the way to associate the method with the tool required.

It probably was not invented as such. Drying the wood until the moisture content is less than what the wood will experience in most situations before gluing it to the ribs helps prevent splitting from compression set. Once the wood rehydrates, the crown is formed by the ribs holding the soundboard at the dry width while the other side of the soundboard absorbs moisture and swells. This shapes the soundboard into an arch.

Or it may be that soundboards were dried by preheating them so the hot glue would be easier to apply, although not as much moisture would be driven out in that process.

So are you thinking as far back as broadwood then? Or even cristofori? Or as Ed suggested Chickering with the first use of a kiln? If Chickering was the first to use a Kiln. The broadwoods that I have seen weren't too cracked and yet didn't appear to be crowned either.

I also don't think it was "invented" as such but for a different reason.

Prior to the late 1920s the only adhesives available to manufacturers working with wood was animal hide glue. One of the problems with this glue is that when it is applied to a cool substrate it immediately begins to cool and it very quickly gels. If it gels even slightly before the two substrates are brought together the resulting bond will be very weak.

With mass production came the need to both speed up the process and to ensure adhesive bonds of good strength the technique of preheating the two substrates was developed. This technique was fairly common in woodworking factories of all types, not just pianomakers.

Gluing ribs to a soundboard panel is time consuming enough that heating both the ribs and the panels became common practice. The wood was heated to facilitate good gluing practice -- the heated rooms were called "hot boxes" for a reson -- but the heating also dried out the panels causing them to shrink but it was the heating that was important, not the shrinking.

Of course once the assembly was reintroduced to the main factory floor they would begin to once again take on moisture and they would warp. Somewhere along the line it was discovered that the soundboard assemblies with a certain amount of warp in them sounded "better" than those that had not warped. The process was standardized and today we refer to the once undesirable warping as "crown."

Whether or not this is the best way to build a piano soundboard system remains debatable.

ddf

The shrinking was important, as well, The relationship between conditioning the panel and cracking was observed at least as far back as Johann Andreas Stein, although the scientific understanding may have come later.

Seems to be considered as a protection for future cracking at the underside of the panel, that a certain amount of compression is to be stored there creating stress on the underside of the wood, not only at the top surface.
(stress is used to raise the resonant frequencies of the assembly, and favor faster reaction of the soundboard to impulses from the strings - hence some noticeable difference in the time it takes for the sound to be formed, depending of the type of assembly)

Whenever curved ribs are used panel shrinking is also used and necessary to avoid the fragility of wood put under stress on the ribs if not.

That is what I find in documentation .

meaning, a certain amount of shrinkage protects the wood from future splitting , limiting the amount of extension of the outer panel may be, I am not so sure of the reason behind it, but that is clearly said.

Now the levels of shrinkage may be less than with the straight ribs : curved cauls way, possibly.

As often some differences with notions and opinions expressed there, or, may I say differences in details or in the way the arguments are proposed.

Got a witnessing too , that a Luwisburg student that made his soundboard using the old hide glue, did get a slightly better sounding result than others using Kaurit (? or PVA type ?).

the Ludwisburg student is literally in need of building a piano for his final exam of piano builder. (a portion of piano actually, I dont know the span)

making the ribs responsible for the elasticity/resilience of the assembly ? One need to think twice about that aspect in regard of the amount of solicitation required to produce a tone (not only resistance to pressure)

Del,
How many systems are there, and which do you believe are in contention?

4 different ways . +- use of panel elasticity

Hi Olek,
If method I described above is one method, then what are the other three you refer about?
Really Curious.

Hi, I PM you to documentation, easier way than rewriting all ...

There are several basic methods of crowning piano soundboards but their precise definitions get cloudy with variations and overlap.

The method most of us are most familiar with—or, at least, think we are—is what I have labeled the pure compression- crowned soundboard system. That this is the most familiar is probably because it is the one that gives the most trouble. The physical limitations of the traditional flat, or straight, ribs glued to a panel that has been heated long enough to cause it to shrink significantly and depending entirely perpendicular-to-grain compression have long been known. By compression stressing the wood making up the soundboard panel beyond its known perpendicular-to-grain compression strength limitations it invites damage at the cellular level to the wood in the long term if not the short term. It also ignores the long term changes that take place due to time related compression set. (It is for these reasons that the wood technologists I have consulted and worked with have a hard time believing we do what we do to soundboard wood.)

The warping of the soundboard assembly that is the semi-predictable result of heating—i.e., drying and shrinking—the soundboard panel and then, in its shrunken condition, gluing on a bunch of perpendicular-to-grain ribs is called crown. Over the early years of the “modern” piano’s development it was widely believed that this crown—once discovered and quantified—was an important causal factor in a piano’ overall performance. We now understand that it was not the warping per se that is important, rather it is the added stiffness the panel’s internal compression added to the system that makes the difference. That being the case some piano builders began investigating how to achieve the requisite stiffness without stressing wood beyond its strength characteristics.

Working still on the premise that it was the crown in the soundboard assembly itself that was vitally important to tone performance, and yet wanting to avoid the problems associated with excessive perpendicular-to-grain compression, many, if not most, piano makers have been moving toward the practice of machining crown into—i.e., pre-crowning—the ribs. By reducing the requirement of drying the panel to the very low moisture content required for pure compression-crowning this lets the builder form what they consider to be adequate crown while avoiding the levels of perpendicular-to-grain compression stress that cause compression ridges, accelerated compression set and ultimate wood fiber failure.

From there, the reasoning goes, if the requisite stiffness can be obtained by properly sizing the ribs—making the ribs taller than they are wide, for example—why do we need crown at all? If the panel is not going to be compression-stressed then why not just size the ribs appropriately, glue up the soundboard assembly flat and be done with it? A potential drawback to this idea was that if any positive string bearing was used the soundboard assembly would not remain flat, it would bend away from the string plane. This has been tried and is called reverse crown and everybody knows that pianos won’t work this way. Or do we? This process has been used quite deliberately with more or less success by several builders. Rippen, for one.

So, if, as some builders believe, the soundboard assembly really should be flat rather than crowned—either positively or negatively—then string bearing of any kind is to be avoided. And this introduces the question of just what the exact roll of string bearing might be in all of this. And this, also, is a question that is being debated today. String-to-bridge bearing—that deliberate stress interface—does seem to be advantageous in some systems (compression-crowned systems in particular) but pianos have been, and are being, built without either soundboard crown or string bearing.

Finally, one of the difficulties in discussing soundboard construction and operation is the considerable overlap that exists in the real world between the various types of crowning and construction techniques used along with the varying ideas of string bearing. And that is just for soundboard assemblies made of solid wood. Soundboard systems using laminated wood panels and composite panels of various types introduce their own questions and proponents and critics.

Just about any soundboard crowning mechanism and string bearing arrangement you can imagine has been used and each has its proponents and its critics. And both proponents and critics can become quite passionate when defending/condemning his/her own favorite.

ddf

One very important function of crown is as an expansion joint. As in all good joinery-the structure must be made in a way to minimize the destructive effects of humidity caused wood movement. Crown IS the expansion joint of the soundboard. Without it, quartered spruce panels would split quite readily in the dry season. Wood in tension across the grain is not very strong.

I think crowing a solid spruce panel without drying it enough is a recipe for premature splitting failures.

There are many compression crowned soundboards that have been housed in reasonably stable humidity that last many decades with no problems. You can't argue with success!

Good resume Ed. And panel drying is presented as at last a protection against cracks in the documentation.

4 basic ways. Panels glued flat or in a crowned gig. Ribs flat or crowned.

Another method is a negative crown, as used by Rippen.

Well, two, actually. Using solid wood panels crown is formed either by panel compression or by pre-crowned ribs. This question is complicated by the fact that pianobuilders use seemingly infinite combinations of the two. Panel EMC and caul shapes are simply process.

In other words, if the details—panel EMC and caul shape—are manipulated correctly then gluing flat ribs to a panel with somewhat higher EMC pressed using curved cauls will give the same end result as gluing flat ribs to a panel having a very low EMC in a press using flat cauls. Both will form crown by panel compression and the resultant stress interface between ribs and panel; different process, same result.

ddf