---------------------- multipart/alternative attachment At 07:01 PM 2/1/2004 -0500, Dale Erwin wrote: >PS I hope somewhere in here is something of an answer/opinion David S was >looking for. No such luck Dale, but, in fact, since this thread moved to "soundboard stiffening", I wasn't expecting one, though I appreciate the thought. As I said in an earlier response (to RicB, I think), I'm trying to stay away from consideration of stiffness, crown, method of construction, etc. It seems to have been exhaustively covered over the last few years, even if some questions remain. But I notice that Ron N has challenged me to be more accurate with my questions, and, judging from his tone, I don't have too many chances left, so I'm off to his post. Good luck to me. David Skolnik >In a message dated 2/1/2004 12:51:33 PM Pacific Standard Time, >fordpiano@earthlink.net writes: >Ric writes > > My own degree of understanding of these matters still remains at a > >rather young stage, yet one theme comes back again and again in > >these discussions. That is that the sound that the panel is able to > >project is dependent upon its stiffness and mass. Certainly any > >particular combination of these is in itself independent of string > >coupling. John Hartman is correct in saying that down bearing can > >increase the stiffness of the panel without added to the panels > >mass... tho the strings have mass to... and these things have a > >habit of working both ways in some sense or another... Still > >essentially John is correct.......... > I think I can hear Del gnashing his teeth. If stiffness was all that > one wished then running ribs at 90 degrees to the grain is the least > stiff configuration. If the ribs are run at substantially less than this > the stiffness also goes up without adding mass. >The question remains then can good sound result without any > >particular amount of down bearing. > > >>. Yes but it would be different. ie many uprights & other grands which > have either lost crown or were designed with very little or i.e. My Own > Mason AA with a minimal crown board (some crown presumably lost) and > light bearing is one of those pianos that works within the parameters > being discussed but it also has a thick board & 15 ribs which equals > mass and stiffness without great amounts of bearing. Also string scaling > is another factor of course. > I just added new bridge caps & no I didn't, & wouldn't set it up with > 0 bearing which answer one of David's question. Why? Because I happen to > think/know that a soundboard with crown or just mass & stiffness behaves > like a compressible spring which makes it more reactive. > I also know that from a tactile sense when I'm prestressing board by > placing wedges under the struts & pounding it down while wedging to > simulate some string preloading that the board simply gets so Stiff it's > like pounding on the bridge top but hitting a gym floor. Its dramatically > different from before prestressing. > The amount of bearing does regulate the rate at which tonal energy > leaves the board/system. Use a garden hose for an analogy turned on full > blast then slowly pinch it to restrict water flow. This I belive is a > simple definition of mechanical imedance. Soundboard compression is also > mechanical impedance but it's impeding soundwaves not water. Phil > correct me if I'm wrong. > David S's question which is ,"does bearing do anything other than make > the board stiffer" I think can be answered by saying I think so based on > what I said above. Its more reactive. Any thing under stress is more > reactive. Humans included > Phil writes > > I keep reading posts by various people stating that the >soundboard gets 'stiffer' as downbearing is applied. But I have seen >no experimental evidence to support this supposition. The only >experimental evidence that I have seen was that presented by Ron >Overs some time back in which he took a crowned ribbed panel, loaded >it incrementally, and noted the deflections. His data showed just >the opposite; that the panel was getting less stiff as the load >(simulated 'downbearing' if you will) was increased. If someone has >some data to support the phenomenon of increased board stiffness with >increasing downbearing then please share it with us. The only >support for this position that I have heard has been anectodal >stories along the lines of, 'I pushed down on the new board and it >deflected, then I leaned on it with all my weight and it wouldn't >deflect any more, so it obviously was getting stiffer'. > > >> I believe it was getting stiffer but remember we're talking about a > light weight system with limited ability to carry loads so great as to > crush them altogether. >It was >reaching a state of equilibrium for the applied load based on the >stiffness of the system. That doesn't mean it was getting 'stiffer'. > There is a difference between preload and stiffness. > > >>I'm honestly not sure about that. It seems like to me it's both. > Was Ron Os demonstation on a board glued to the case liner? For the > board will certainly react differently if the test is out of the piano > with out the edges glued down. >As you >apply more downbearing load to the board then the preload (or >prestress if you prefer) will increase. It's not hard to believe >that this could have some affect on the vibrational characteristics >of the board and experience tells us that it does. Putting >downbearing on the board usually seems to have a beneficial effect. > > >> And too much makes for a stingy sound especially in the treble > > Stiffness is a relationship between load and deflection. If two >beams have the same load applied to them, then the one that deflects >less is 'stiffer' for a load applied at that particular spot. >Increasing stiffness under load would mean that there was >incrementally less deflection for unit increases in load. If a beam >deflects down 1/10 of an inch for an applied load of 1000 lbs, then >if it is getting 'stiffer' under increasing load, when you applied an >additional 1000 lbs of load the additional deflection would be less >than 1/10 of an inch. > > This is exactly what a board is doing when it is being compressed up > to a point & then it will fail just as the beam will. > I see no reason why a ribbed panel would >behave in this way. That's not to say that I can't be wrong and that >there's not something about this particular system that I've >overlooked or don't understand. But I'd like to see some >experimental evidence to prove it. > This distinction is important to potential soundboard design. >If the important thing is increasing the stiffness without increasing >the mass, then an alternative soundboard made of something like >honeycomb sandwich might give the desired performance without any >downbearing. If the important thing is preload or prestress in the >panel then the honeycomb panel might be a waste of time and >downbearing would be essential regardless of the type of panel you >used. > Also, if the board is not getting stiffer as a result of >deflection, it raises the question of what function the crown is >performing. > > >>The way I look at it is that putting boards under some modest amount of > strain via compression or tension for that matter makes the board more > reactive and tonally efficient because of the impeding effect, which > moves air & thet's why soundboards are built this way. If it wasn't Ron O > would be building a flat board. >If the crowned board is not getting stiffer as it >deflects down, then a flat board would be just as stiff as a crowned >board. So, the reason for the crown would not be 'stiffness'. > >Phil > >> But I think it is getting stiffer. > Dale >PS I hope somewhere in here is something of an answer/opinion David S was >looking for. ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/c6/b0/be/c0/attachment.htm ---------------------- multipart/alternative attachment--
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