Robin and other interested parties, I've been following this thread all the while. No I haven't been ignoring you all, I've just been caught up in a local battle for a pianist's right to use our piano in the 2002 Sydney Festival. We just got approval for this on December 22, hence my absence from list discussion. I'm currently on holidays until the weekend, but I've got a computer with me since I'm designing a new grand piano at present. For those who may be interested in the concert details (or even attending if you're not too far around the horizon), David Bollard will now be playing our piano no. 003 in the 9.00 pm concert of January 20. Details can be found at; http://www.sydneyfestival.org.au/events_detail.asp?id=10 > Robin wrote; > . . I have repeatedly stated, as I did in the first post, that >the answer to >this question is to be found in the analysis of motion itself, referring to >the nature of translation, rotation and stress wave, another point >you, Del and >others took no pains to comment upon. Nevertheless I can't imagine how anyone could disagree with this. While I didn't comment at the time since I was involved with other matters, I haven't got figures for bridge rocking at present. However, since this appears to have become such a hot issue, I will try to devote some attention to it when I return from holidays (by getting some real figures). I have no desire to get into a full blown debate on the issue since I am not concerned if others don't share my view, but I would be prepared to derive a few figures on the matter. >. . . . Ron [N], you, at least insofar as I am concerned, to your >credit, have been >willing to get in the trenches and debate these issues, while your >co-proponents are apparently busy elsewhere, this being the holidays perhaps >that is understandable, perhaps not. Yes sorry Robin, but we do have to earn a living also from time to time. >There is far more than merely the >"tension difference" inhibiting your rocking motion. The forces exerted on >the bridge which itself is stiff expressed as the downbearing load or to use >Del's term "downforce" are counterbalanced by the resisting forces >provided by >the soundboard assemply including the ribs, the strain of crownd, >the rim, and >so forth. True, but the apparent stiffness of the bridge will not prevent it from rocking as some have asserted (particularly if the bridge height is not too low). A bridge will 'rock' just as a relatively stiff rim will flex when the case is leaned upon (I have tested this with dial gauges previously - and written about it on the list). Similarly, an engine block will flex when subjected to a moderate hand force. For those of you who are "doubting Thomas's", confirm this with an engine reconditioner. Place a bore gauge in the bore of a freshly re-bored cylinder (in order to test this the bore must be true), the bore gauge will be capable of supporting its own weight in the bore. Now flex the engine block (by hand) across the cylinder bore and perpendicular to the orientation of the bore gauge. The gauge will then fall out of the cylinder. One could conclude from this that rigidity is and will always be relative. Therefore, when the vibrating string goes through a cycle, its tension (which varies slightly as the speaking length is offset from its resting position) will cause the bridge to flex slightly backwards and forwards (in a vector direction parallel to the axis of the speaking length) in response to the speaking length deflection also. Because the vector force on the sound board panel is a product of the string tension times the SIN of the string deflection angle, the downbearing force will vary similarly to that of the speaking length during the cycle. Therefore, the board will respond to the position of the speaking length string segment at each point in the cycle. This is I believe the most important physical factor which causes the sound board to respond to the vibration of the speaking length segment. Now Robin, I do not at this time have numbers to support my philosophy here. Previously, I didn't feel it necessary to produce a set just to understand how the process works. Similarly, I suspect that Charles Darwin had a strong idea of the theory of evolution well in advance of his voyage on the Beagle (I have read 'The Origin of Species' but it was a while back). His long held view was merely confirmed in an ever increasing way as he gathered more information. I have carried the 'rocking' theory with me for at least fifteen years (long before I ever knew Ron N and Del existed), and all the while, thinking about the many different pianos we've rebuilt (as each one has come along) has re-inforced my view. Even Bösendorfer seem to be demonstrating an understanding of the principle in their later pianos by undercutting their dog-leg breaks to allow a more uniform bridge stiffness. The 'dog-leg's wider footprint, if not undercut, will tend to 'close' the sound at the breaks (this is just one more piece of evidence which supports the bridge-rocking theory - perhaps not to everybody's satisfaction but ah well). I have undercut dog-legs on many occasions, only to find that the sound improved to my subjective ears. But please don't accept this idea if you don't want to. I am not prepared to debate it ad nauseum, since I'm currently designing two new grand pianos. But when I get some numbers I will advise the list of my findings. Regards to all for the Christmas break. Ron O -- Overs Pianos Sydney Australia ________________________ Web site: http://www.overspianos.com.au Email: mailto:ron@overspianos.com.au ________________________
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