This is a multi-part message in MIME format. ---------------------- multipart/alternative attachment ----- Original Message -----=20 From: "Greg Newell" <gnewell@ameritech.net> To: "Pianotech" <pianotech@ptg.org> Sent: May 09, 2003 3:46 PM Subject: Re: Modal Analysis Del, I wonder if you might help me understand this. You say, "And a=20 good example of why soundboard cutoff bars can (should) be used to some=20 advantage." In the views I saw on the web page there seemed to be quite = a=20 bit of movement in the area normally eliminated by a cutoff bar.=20 Yes, and it is exactly out of phase with the motion of the bridge and = the area of the soundboard surrounding the bridge. ---------------------------- If there=20 is that much movement is that not contributing to what we hear rather = than=20 detracting from it? As I type and look back at the pictures in another=20 window I'm tempted to rationalize that while one part of the board,=20 specifically that part in question, is on the down part of a wave the = rest=20 of the board is up and visa versa. Is this what you wish to eliminate = with=20 the cutoff bar so that the board acts as a whole instead of in separate=20 parts? It would be interesting to see what the board would do using this = modal analysis with a cutoff bar installed. Yes, this is what I am trying to eliminate with the addition of a = carefully placed cutoff bar. Energy is being traded back and forth and = is essentially being wasted. Going back to my analogy of the piano = soundboard functioning somewhat like loudspeaker driver: the soundboard = functions best when it is appropriately sized for the frequency range = through which it is expected to function. If it is too small it is great = for sustain but will not be able to develope the desired power. If it is = too large, however, both sustain and power suffer. Sustain because = energy is being wasted in the excess soundboard area and power because = acoustical energy is being traded back and forth between the various = resonant areas and is effectively cancelled out. ---------------------------- This brings me to another question. In all of the examples I've = seen of pictures with cutoff bars installed, all seem to be a great deal = smaller in size than the corresponding inner rim section they are=20 replacing. I understand that they are epoxied into the existing inner = rim=20 and doweled as well. I further understand, I think, that the cutoff bar = is=20 attached to any support beams over which it passes. Do the combinations = of=20 these items make it unnecessary that it be of similar dimension as the=20 inner rim? Yes. That and the fact that they are generally rather short. Early on we = did try to make them somewhat more massive but over time have found that = this is not really necessary. I don't have any formula for this, I just = look at the thing and decide. If it is quite a long cutoff I'll make it = taller. Del ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/4b/72/f5/0b/attachment.htm ---------------------- multipart/alternative attachment--
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