> Stephen Birkett wrote: > Rigidity and mass of the case are two independent parameters. The > stiffness of spruce is actually extremely high, but mass is low...which is > why it is used for sbs. Hardwoods are not much stiffer, but have a lot > more mass. Case construction is also an important variable (e.g. > framing)...but this is less significant in pianos with iron frames, since > all are much the same in effect... Stephen, The iron plate has less to do with stiffening the rim assembly (acoustically) than you might think. Except in the case of pianos with "full-perimeter" plates that are fully fitted to a soundboard upper liner (a carefully fitted hardwood strip glued to the top of the soundboard and running the full perimeter of the soundboard--except for the front edge along the belly rail--that the plate is in solid contact with) the plate does not actually affect the rigidity of the rim all that much. Most plates do not contact the rim at all along the straight side where most of the losses occur and where they do make good contact (along the curved treble side) the rims of most American built pianos are already so massive and stiff that the plate has very little influence. ddf
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