On Wed, 27 Mar 2002 08:56:09 Delwin D Fandrich wrote: > > >Energy--'vibrations'--imparted at a specific spot on the bass bridge aren't >expected to travel to 'all parts' of the board. They are expected to cause >displacements of the soundboard panel in the bass region. > > >I also find myself thinking about the structure of the bass >bridge--typically made out of maple, or some similar hardwood, with a width >upwards of 32+ mm and generally well over 50 mm tall--and comparing this >with the structure of the ribs in question which are generally spruce or >pine and something less than 25 mm in cross-section. > > Both of these seem to me to be reasons for not having a very stiff bass bridge. If you want the energy to transfer to the board locally, then having a stiff and long bridge it's going to tend to spread over the whole length of the bridge. If the bridge was very flimsy it would seem to me that it would want to spread to the adjacent ribs, which is where the stiffness would be. Which brings up the second point - if the bridge is very stiff relative to the rib stiffness then it is the bridge that is controlling or dominating the stiffness of the system locally rather than the rib and soundboard stiffness. It would seem that you lose your ability to control or tailor stiffness with the rib and soundboard configuration by making the bridge too stiff. >> >> 4. To provide stiffness to the soundboard, rib, bridge system in addition >to that >> provided by the board itself and by the addition of ribs to the board. If >this is >> the primary function then it seems you would want more stiffness at the >top end >> and less stiffness at the low end. So the bridge might be taller at the >top end. >> Perhaps items 3 and 4 balance each other out so that the bridge should be >the >> same height all along. > >Could you explain this point a bit more? I don't see why you would want more >stiffness at the top end and less at the low end. Certainly reduced >stiffness is appropriate between the bridge and the inner rim, but I don't >see why the bridge itself would need to be more or less stiff at any given >point along its length. At least I don't see a practical reason for the >notion. I thought that what you wanted was for the treble strings to 'see' a high impedance - (excuse me if I'm using that term improperly) and the bass strings to 'see' a low impedance. At the top end one way to do this is to make the board thicker. Another way is to add more or stiffer ribs. Another way, it seems to me, is to use a stiffer bridge which will tend to spread the local load over more ribs and more of the soundboard to give a higher local stiffness at the point of load application. At the bottom end the opposite is true. In order to lower the impedance then one way to do it is to make the board thinner. Another way is to make the ribs more flexible or use fewer of them. Using a stiff bridge to spread the local load over more ribs or soundboard seems to be working against you. It seems you would want the bridge to be as flexible as possible so that the stiffness is being controlled by the ribs, but not so flexible that there is a difference in sound between notes over the ribs and notes between the ribs. >And, in response to that marketing department, I would say they are also >placing greater stress on the plate; contributing to the piano's >instability; making routine tuning--specifically, pitch raises--more >difficult. >Del > What are the reasons for these things? Phil F See Dave Matthews Band live or win a signed guitar http://r.lycos.com/r/bmgfly_mail_dmb/http://win.ipromotions.com/lycos_020201/splash.asp
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