>> . . . . When the >> mere act of touching the bridge pin terminating a beating string clears up >> the beat, it ain't the soundboard design, or is it? > >Yes. You're altering the resonant frequency of the soundboard by touching the >bridge pin. More anon... *When you then CA the pin, and the beat stops even though you are not touching the pin, it's the pin. When you touch the pin NEXT to the pin terminating the beater and the beat doesn't stop, it's not the alteration of the resonant frequency of the board by touching pins that makes the difference. >It's not even so much a matter of soundboard system crown. I'm not convinced that >within reasonable limits the lack of crown and/or bearing has much of anything to do >with pins coming loose or staying tight. It does have to do with soundboard >springiness. *Nope, I didn't say anything at all about crown /bearing affecting pin tightness. The pins get loose because the bridge changes dimension with humidity swings and wood is crushed. There is a fair amount of continual side bearing on the pin courtesy of the stagger so you can add some cumulative compression set. The harder and more dimensionally stable the bridge cap, the slower the pin loosens with time. These false beats tend to be in the killer octave and are worse when the bearing is light. >OK. So, here is the short and sweet version of the principle: > >If the fundamental resonant frequency of the string loaded soundboard assembly at >the point of contact with the affected string is higher than the fundamental >frequency of the string, the motion of the bridge tends to follow the motion of the >string and the string sees both the actual speaking length and some artificially >longer speaking length. False beats will readily develop and will be nearly >impossible to control. > >If the fundamental resonant frequency of the string loaded soundboard assembly at >the point of contact with the same string is lower than the fundamental frequency of >the string, the motion of the bridge will tend to oppose the motion of the string >and the result will be a cleaner, more efficient termination of the speaking length >of the string. False beats will show up more rarely and will be easier to treat. *The fundamental resonant frequency of any area of the soundboard system will be dependant on the impedance of that area. Less mass and more stiffness in the treble, and more mass and flexibility in the bass. That's woofers and tweeters. If the killer octave area in a traditional system is too low in impedance for the frequency ranges it needs to handle, by being too flexible, then it's fundamental resonance frequency is lower than it needs to be as well. By what you outlined above, this area should be relatively free of false beats and easier to treat, should any happen to arise. That's exactly backward from what I see in pianos - does not compute. Also, the bridge is just that... a bridge. It's job is to provide string termination and convey energy back and forth between the soundboard assembly and the string plane. The tenor/treble bridge extends from the lowest impedance areas of the board, to the highest. It is highly unlikely that at any point along the bridge, the soundboard system impedance measured at the string termination point equals that of the soundboard directly beneath. The stiffness of the bridge averages impedance loads of both the string plane, and the soundboard assembly. This should make the killer octave seem somewhat less bad than it actually is, and maybe it does, but there is still some flexibility there, and it is still evident, though blended at the boundaries somewhat. The point here is that if the fundamental resonant frequency of the soundboard is supporting false beating strings, All the strings in a range should beat similarly. If, for instance, the left hand string of A6 beats, and the middle string does not, why not? If it's a general problem, the symptoms should not be so specific. When I run into a lot of false beating strings in a given grand, I check bearing. The beginning and ending limits of the range of false beating strings corresponds closely to a range of lower to non-existent bearing readings. I assume there was adequate bearing, for the most part, in this area when the piano was strung, but it lowers quickly in service. This is the section of the board that usually goes flat first, and that's a design problem. Nearly all of the beaters clear up with pressure on the pin. Some do not. Why? The ones that don't, tend to be a less distinct sounding beat than the loose pin beat. I don't see any reason not to blame impedance mismatching and resultant fundamental resonance frequency mismatching, at least partially, for these. That's a design problem too. That leaves the bulk of the killer octave beaters still under the loose bridge pin column for me, at least from a service perspective. >I agree that you have to do whatever you can to attempt to make these things go >away. Just don't beat yourself to death if your best efforts are not all that >successful. It ain't your fault. *So far, I have steadfastly refused to accept blame for false beats since I started in this business. We'll see. > >> They'll be using different glues too. > >What? Better than CA . . . . ? How could that be? *Just you wait. Some day they'll have glues that make pianos better just by un-capping them in the vicinity of the ailing instrument. You'll be able to glue your fingers together just by reading an ad for the stuff in the Journal. I'm lobbying for the name "Resurrectum", but nobody seems interested so far. Go figure. >> Serves you right, troublemaker. Did you get your head working? <Evil Grin> >> > >Which "head" are we talking about here, Ron? If we're talking about the one on the >boat, yes. At least it's working about as well as it's going to work. If we're >talking about the one I normally carry around with me -- well, that one hasn't been >working right for years.... > >Del Yea, I meant the one in the boat. The portable one seems to work fine except for your tendency to go off and leave it running. %-) Oh well, my Dad used to yell at me about leaving lights on too. Tag, Ron
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