----- Original Message ----- From: "David Skolnik" <skolnik@attglobal.net> To: <pianotech@ptg.org> Sent: March 29, 2002 10:09 PM Subject: Re: Case separation or delamination question > .... > The piano in question is an old Steinway C (?) 85 note from about > 1883....The delamination between inner and outer rims goes > completely around the perimeter. The visible gapping is generally from 1 > to 2mm. I only had a flat steel handled upright mute (.5mm or .020") to > use as a feeler gauge & it tended to insert between 1 to 2 inches throughout. Well, this is certainly more than a slight separation. Borders on "Can you take the outer rim off and still have a working piano?" This delamination you describe--are you seeing it from the top or the bottom. Or both. Does it go all the way up or down? Can you see air all the way through? > > The piano was recently rebuilt (within the last year and a half). There > have been significant tonal deficiencies, especially in the 5th and 6th > 8ve. From the 7th rib up there is no apparent crown. I didn't notice the > delamination when the piano first came back, but, in spite of a few months > out of the year of rather low humidity (20%), I doubt that such a degree of > separation would have happened in such a short time. Have the tonal deficiencies been apparent from the start? Or have they developed over time, i.e., did the piano sound acceptable immediately following the rebuilding and then deteriorate? Or was the tone unacceptable immediately following the work? You are probably right, the rim delamination probably did not happen in just a few months. But changing weather conditions might cause it to appear and disappear. Did you have any reason to look for gaps before the piano went to the rebuilder? Is it possible that the gap could have been closed while at the rebuilders shop and then open up when it returned to your environment? This does seem like quite a gap, but still.... > > The main question for me is, what design parameters are impacted, and to > what degree, when there exists a significant amount of inner rim -outer rim > separation of a unified rim design. I doubt the loss of crown is attributable to the rim delamination but would not want to go too far out on the proverbial limb without being able to personally examine the instrument. Rims don't have much to do with either forming or maintaining crown. There is a lengthy explanation and you'll find it in my articles dealing with soundboards in the Journal. Obviously, if the delamination is from the top down the rigidity of the soundboard termination will be affected. Sustain time will probably be reduced either with or without a loss of crown. Steinway couples some of the stress from the strings down through the plate horn to the bellybraces but these butt up against the tail of the inner rim so I doubt there would be much loss of structural integrity. Again, without actually being able to examine the instrument.... > > What are the sources of stress in a single rim construction? The initial > bending creates the classic tension/compression stress. Spreading the arms > to fit the pinblock relaxes some of that stress, but stresses the cured > glue joints. Some stress is transferred from the strung plate. and perhaps > some outward stress from the compression of the soundboard. Some of the > stress is internal, some imposed. Would the acoustical properties of the > rim change over time, as the internal stress dissipates? I can only speculate on this question, but I doubt there is much acoustical change. I've looked at rims only a few years old that have come completely apart due to really poor gluing practices and have found the veneers have taken enough of a set to pretty much hold the shape of the piano without any glue integrity at all. I've no idea how long it takes for rim veneers to reach this point. It would depend on the species of wood used and how thick the veneers are. Steinway uses rather thick veneers so it might take a few years. I suspect it also depends on how the rim is treated both in the press and how it is conditioned later. If the press is heated and the conditioning takes place at elevated temperatures this stabilization will take place more rapidly than it will if the rim is cold-pressed and conditioned at room temperatures. I don't know how much more rapidly. > > So, what purpose does the outer rim serve, in a Steinway? Would you > suspect any discernable difference between a Steinway built in the > traditional manner and one constructed with a 2 part rim? For that matter, > when did Steinway begin unified rim construction? The outer rim in a Steinway piano serves the same purpose it serves in any other piano. It is certainly a significant part of the structure but no more so than it would be if the rim were pressed in two pieces and later joined. I don't know when--or, for that matter, why--they started the practice. > > In an older instrument such as the one I have described, I would assume > that most, if not all of the original internal tension has relaxed. I'm sure it has. Probably about 100 years ago. Give or take a year or two. > > Unless > the outer rim contributes to rigidity of the soundboard mounting, affecting > crown and energy reflection, the only reasons I can see addressing rim > separation would be either cosmetic, to prevent potential transient > vibrations, or to keep it from getting worse. Have I misunderstood or > misstated your position, or does this correctly reflect your thoughts? Well, a separation this extensive could conceivably affect several things. It will affect the stiffness felt by the soundboard. It will also affect the apparent mass felt by the soundboard. Both of these factors will have an effect on tone performance, principally sustain time. I still stand by my assertion that the rim separation probably did not affect soundboard crown. I am not aware of any tests that have indicated the rim is capable of supporting crown. Nor has anyone ever presented anything like a compelling argument that the rim is capable of doing this. I think you'll have to look elsewhere for both the cause and solution to the crown problem. I would certainly address the rim separation problem for the reasons I've mentioned above as well as to prevent the cosmetic changes that will occur when the outer rim falls off the piano. Regards, Del
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