Aggreed from most of the workshop guys there and there. But indeed it should be done anyway. And about the large articles of the Journal "with formulas" I always have find that in the next isssue someone wad other formulas just to prove the opposite. Piano trade is a wondeeful word (and i am the only one to know what tones well !) Best Regards. Isaac OLEG Entretien et réparation de pianos. PianoTech 17 rue de Choisy 94400 VITRY sur SEINE FRANCE tel : 033 01 47 18 06 98 fax : 033 01 47 18 06 90 cell: 06 60 42 58 77 > -----Message d'origine----- > De : pianotech-bounces@ptg.org > [mailto:pianotech-bounces@ptg.org]De la > part de Delwin D Fandrich > Envoyé : mercredi 30 juillet 2003 21:53 > À : Pianotech > Objet : Re: soundboardinstal again > > > > ----- Original Message ----- > From: <ranjacob@umich.edu> > To: "Pianotech" <pianotech@ptg.org> > Sent: July 30, 2003 10:11 AM > Subject: RE: soundboardinstal again > > > > Right, bridges serve to distribute load among the ribs, and don't > > support crown, and I was asking whether or not a counter-bridge or > "sister > > bridge" had ever been intended, at least partly, to > support crown. Or if, > > without adding way too much stiffness and mass, a set of > counterbridges > (or > > better, quasi-ribs parallel to the grain of the panel) *could* be > designed > > to support crown, so that, *assuming* there was anything > to be gained > from > > it, ribs could be designed without having to have all of the crown > support > > as one of their functions. > > Yes, a bridge system could be designed such that it would > "support crown." > As to whether that is desirable or not is another question. > With this > subject coming up so regularly it has given me some reason > to think about > it some. I'm not at all sure this would be a good thing. A > bridge that > would be so stiff and structural as to be effective as a > crown-supporting > member would (regardless of the mass involved) also be an > overly effective > acoustical bridge. That is, it would spread the energy from > a particular > string set (at a particular frequency) over too broad an > area. There is a > reason why the flugal, or wing-shape, design has won out > over the years. > > > > > > I think that due to Del's reply and yours, I see better > why this might > not > > work, or, at least, might be wholly unnecessary. > (Understand, by the way, > > that I am after grand piano tone, not, what might result > if we tried to > > "simplify" matters by pretending that we are trying to > reproduce string > > oscillations as found at the bridge cap, in the same way > that an audio > > engineer tries to reproduce air oscillations arriving at > a microphone.) > > Gosh, and here all the time I thought that was just what we > were trying to > do. > > > > > > One way of visualizing the problem lies in considering > the consequences > of > > the fact that the gaining of downbearing necessarily > changes, from a > right > > angle, the angle of the string to the downward vector of > board assembly > > movement. (The assembly does have very high resistance to > any change in > the > > exact angle at which its own deflection, as a complex of > end-supported > > beams, operates in response to the "live load" bearing > down on it. ((Now, > > *there's* a simplification...)) :) .) Rather than being > merely "just a > > very small change of angle", this lessening of the right angle > > fundamentally alters the right angle that is shown in a > drawing, on > > acoustic theory of the string, of the string as having > one vertically > fixed > > termination (the capo or agraffe) and one termination > that is fixed > > horizontally, but whose vertical "quasi"-fixing is to a > mass that is free > > to move vertically -- e.g., a mass free to move > vertically because, in > > fact, in that dimension, it is a spring. That is, the > change from that > > right angle to a smaller angle in the grand piano will > cause the string > to > > have more tension than its resting tension at the top of > its complete > cycle > > of vertical oscillation, and less tension than its > resting tension at the > > bottom of the complete cycle. These differences cancel > each other out, > > yielding a tone that is steady in pitch, just as the > process of the > > formation of the string's standing wave after the upward > blow of the > hammer > > is, in part, a process of cancelling out certain of the > effects of the > > blow's having been upward rather than downward. > > > > It is, therefore, this lessening from the right angle to the > > assembly's vector as a spring that makes the string itself > > an *opposing* string, in the sense that, at the required times > > in the course of the fundamental's cycle (and, > correspondingly, of the > > cycles of the harmonics), the string is a not "simply" a > > spring that hardens when moving upward from the rest position > > of zero amplitude, but a spring that has the required degrees of > > stiffness at that rest position and at all higher amplitudes. > > The provision and adjustment of the adjustment of > downbearing, therefore, > > is a means to control the rate of vertical transmission > "beyond", and, so > > to speak, horizontal reflection backward from, > > the coupling of the string to the bridge. > > This is a good way to go nuts! It's time for a little > simplicity. Varying > string bearing against the bridge controls (varies) the > amount of string > loading against the soundboard system, hence the spring > rate of the system, > hence mechanical impedance of the system, hence the rate at > which energy is > transfered from the strings to the soundboard system. > > If you're really determined to add in some complexity this > would be a good > time to consider the effect of the string backscale on the > bridge/soundboard system. > > > > > > If I haven't made a new mistake here, my next question is: > > are *lateral* transverse vibrations of the string (or, > large lateral > > vectors of vibrations that are significantly "slanted" > from the vertical) > > thought to be transmitted in any way that the theory > > of the board assembly, and of the interaction of its components, > > has been able to explain, or (usefully) speculate about? > > This would depend on your defination of "usefully." In > terms of piano > design I can't see how pondering this line of speculation > could be usefully > applied. From a purely scientific perspective it may well > be usefully > considered and studied. This all goes back to something I > have observed > several times in the past--there is much scientific > exploration into the > physics of musical instruments that has been largely useless in the > development of those instruments. That doesn't mean it > shouldn't be done, > it just all needs to be kept in perspective. > > Del > > > _______________________________________________ > pianotech list info: https://www.moypiano.com/resources/#archives
This PTG archive page provided courtesy of Moy Piano Service, LLC