Danny Moore wrote: > Antares wrote: > > > So if you have a beautiful sounding soundboard and it is old and has lost its power. What gives a board power? right! the ribs. > > OK, I can accept that, but why "new" ribs on an old board? If the board was truly a beautiful sounding board, it was a result of the whole thing, including ribs. This logic was why our teacher taught us to remove the board, cook the humidity out of it, > and glue the original ribs back on in the facory location. This restores the crown without changing any of the original characteristics.... This may restore some of the crown, but the original strength characteristics of the wood are long gone and will never be seen again. The culprit is compression set. Most soundboards installed in pianos prior to the second half of this century were compression-crowned. This means that from the day they were born the wood fibers were under quite a lot of compression. As the soundboard aged, crown was lost because the wood fiber took on permanent compression set and some amount of compression was lost. Wood fiber that has undergone compression set has been permanently and inalterably damaged. If I understand what you are talking about above, you were reusing the original ribs and once again placing the soundboard under compression. This will hold for a while, but not as well or as long as did the original installation. The already damaged wood fiber simply will not be able to hold up under the additional compression. If I understand the process Andre is talking about correctly, new ribs are pre-crowned and glued onto the soundboard in place of the original ribs. This does alter the acoustic design of the soundboard somewhat, but it also takes some of the compressive load off of the wood fiber. The original panel is now functioning as a simple two-dimensional wave carrying medium -- which is what it should have been doing from the beginning. > Of course one would have to be careful not to destroy the angle of the inner rim, and (as a result of many years) the rebuilt board will be slightly smaller than the rim, so the "gap" between the board and the rim must be filled (we used epoxy). > > > In Holland we have a funny expression : "Kat in het bakkie" > > Yeah, well I generally have better luck getting Kats to do what I want than I do soundboards. > > Danny Moore > Houston Chapter -------------------------- The gap between the edge of the board and the rim is the result of the afore mentioned compression set. Filling this gap is really optional. It will look better cosmetically, of course, but there is enough glue surface on the inner rim to adequately hold the soundboard in place. -- ddf
This PTG archive page provided courtesy of Moy Piano Service, LLC