I think there are two issues. One is impedance matching (or lack of) between the low end of the tenor bridge and the top end of the bass bridge. The other issue is resonant frequencies when there is a sympathetic match between a certain note and a section of the soundboard that it excites. David Love davidlovepianos@comcast.net -----Original Message----- From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On Behalf Of David Ilvedson Sent: Friday, January 21, 2005 7:02 PM To: pianotech@ptg.org Subject: RE: Impedance problem So is this like on some small grands and the first tenor note or so kind of booms out...? David I. ----- Original message ---------------------------------------- From: Ron Nossaman <rnossaman@cox.net> To: Pianotech <pianotech@ptg.org> Received: Fri, 21 Jan 2005 18:31:20 -0600 Subject: RE: Impedance problem >>I didn't weigh it but it was a very small one that I use for making >>loops for string knots. On second thought it seems like not enough mass >>to have an influence on impedance so soundboard resonance makes sense. >Right, and an impedance change wouldn't be so note specific, but rather >more general to the area. >>What is it that causes that to happen and how is it generally avoided in >>design? >> >>David Love >Consider a soundboard a driven harmonic oscillator. A sprung mass system. >When the resonant frequency of the assembly at the driven point is the same >or close to the same as the driver, the soundboard moves in phase with the >driver, increasing in amplitude and draining the driver's energy quickly. >It sounds loud and short. Lower the resonant frequency of the soundboard by >making it either heavier or less stiff, and something different happens. >The phase of soundboard movement lags behind that of the driver, opposing >movement rather than reinforcing it, so the soundboard moves at a lower >amplitude, and absorbs the driver's energy more slowly. It sounds less loud >for longer. Avoiding it in design is partly luck, depending on the >soundboard construction method, and partly ignoring it when it happens. >Adjusting it after the fact by mass loading the bridge is easy enough, and >doesn't otherwise muck anything up. >Ron N >_______________________________________________ >pianotech list info: https://www.moypiano.com/resources/#archives _______________________________________________ pianotech list info: https://www.moypiano.com/resources/#archives
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