----- Original Message ----- From: "Calin Tantareanu" <dnu@fx.ro> To: <pianotech@ptg.org> Sent: August 10, 2003 10:36 AM Subject: Soundboard crown > Hello! > > I have followed the numeorus discussions on this list oabout rib-crowned vs. > compression crowned soundboards with great interest. > However, I am asking myself if a soundboard always needs crown in order to > work properly? > I heard about some old pianos with no measurable crown that sound very good. > I have even seen some where no crown seemed left, yet the performance was > very good. I read that harpsichords do not have crowned boards (except the > Italian ones). > So, why is a crown necessary? > Would a flat board, but with enough downbearing for teh strings, work or > not? > > Regards, > > Calin Tantareanu > ---------------------------------------------------- As a purely theoretical question, I would say definitely maybe. There are, of course, a number of qualifiers, variabilities and dependencies.... Soundboards, of whatever nature and material, need a certain combination of mass, stiffness and internal resistance to function in the way in which we have become accustomed. (For the purposes of this discussion let's ignore the effects of humidity and wood MC on any part of the soundboard system.) If we deviate overly much from the parameters that have evolved over the centuries we will no longer have an instrument definable as a piano. History defines the tone standard we are striving for. Or at least it did until the flood of piano-like objects with their granite hammers and their massive marketing campaigns arrived on the scene. In 1700 wood was the only logical material from which to make soundboards. And it remained the only logical material until fairly recently. While the piano soundboard started out as basically an overloaded harpsichord soundboard, it had evolved considerably by the late 1800s. The motivation for this evolution was the increasing demand for power and the resultant string loads placed on them. In response it became thicker and, by virtue of increasingly stiff and massive rib systems, stiffer. Using construction techniques that seemed reasonable to piano makers of the day, one viable way to achieve an adequately stiff soundboard system without overloading it with excess mass was to form a positive wood spring and then compress it with another spring--the string set that was stretched across the bridge with some amount of tension and deflection. In so doing the stiffness of the soundboard system was increased considerably with no increase in mass. With all this in mind, if we are to deviate from the established pattern we must come up with a soundboard construction having a mass that falls within certain limits combined with an amount of stiffness that will control the rate of energy transfer from the vibrating string(s) to the soundboard panel. One can argue that what the soundboard needs is stiffness, not crown. If the requisite amount of stiffness can be obtained sans crown a workable soundboard can readily be built without it. Certainly this was accomplished by Rippen with their laminated soundboards. These boards had no crown as built, though they did end up with "negative" crown through string loading. Nearly any degree of stiffness (within reason) can be obtained with a standard wood panel/rib combination by simply making the ribs as tall as need be to achieve the desired amount of stiffness--without any crown being included at all. The mass of these ribs can easily be controlled by simply making them narrower. And this is basically what we do when we make a rib-crowned soundboard system. The ribs, instead of being anti-crown devices, now become structural beams with their stiffness being controlled by their cross-section height and width coupled with some projected amount of deflected crown. By removing crown from the equation we could still come up with the same amount of stiffness by adding a bit more height to the ribs. Having come this far, we must now bring up the question of whether or not string deflection in the form of string bearing working against the soundboard is really necessary. The traditional string set/soundboard system works on a principle of two opposing non-linear springs--the soundboard system pressing up against the string set which is pressing down against the bridge/soundboard system. Now, is our crownless soundboard going to have any string bearing? If so, is the soundboard going to start out with some slight crown and become flat through the application of that string bearing? Or is it going to start out flat and be forced into some kind of reverse crown by the string bearing (ala Rippen)? Or is it going to start out flat and remain flat having the strings attached without any deflection, hence no string bearing against the bridge? Keeping in mind that I've not done much of any real research specifically designed to resolve these questions, I do have a couple of thoughts. A system in which a string without deflection is working against a flat soundboard is not going to respond like a system in which a string with deflection is working against a sprung soundboard system. Considering just the soundboard, in the first configuration--both the string and the soundboard system working through their zero axis--the soundboard's stiffness will be least at its rest position, increasing somewhat as it is forcibly deflected from rest by the motion of the vibrating strings working through the bridge(s). In the second, the stiffness of the soundboard system increases as it is forced down and decreases as it returns and moves up beyond its rest position. The opposite effect is seen in the string set. As to exactly how much difference this makes in the final sound envelope, I don't know, I've not attempted to define and measure it. I suspect, though, that if two pianos were built having carefully controlled soundboards, one being designed to have a given amount of mass and stiffness with no crown and no string bearing and the other being designed with just enough crown so that it would become completely flat with some amount of string bearing (and at that point having exactly the same mass and stiffness as the first), the latter piano will have a better balance between power and sustain. I suspect that the first piano would have a somewhat more percussive sound and, consequently, a shorter sustain time. It would be an interesting experiment, but lacking that we are not left without clues. We can come close to this in real life by examining a selection of otherwise nicely rebuilt pianos having old soundboards that have ended up little or no discernable crown after stringing. I've encountered examples of both: freshly rebuilt pianos with zero crown and no measurable string deflection and freshly rebuilt pianos with zero crown--i.e., some distorted but with the bridge line at the same elevation as the outside edges--but with some string bearing. Yes, they both work, but it becomes a judgment call as to how well they work. In general the respective pianos have exhibited the tonal characteristics described above. Del
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