Roger Jolly wrote: > Hi Jim, > Thanks for your reply, however you do live in sunny Florida, 60% RH > is probably your extreme low. It is not uncommon to get indoor lows of 20% > and less in this neck of the woods during winter, in fact we are drier than > the Sahara Desert. > As I understand from the Yamaha personel, and techs that have > participated in there 5 week C & A grand training prigramme in Japan, they > do in fact have several production standards, to suit the final > destination. The super dry specs for our climate would give another type > of problem in other destinations, (e.g. Pressure ridges in sound boards > etc.) ----------------------------- Roger, Whatever other problems you may encounter with these pianos in the climate you describe, pressure ridges in the soundboards should not be among them. Pressure ridges are caused by a build up of internal compression within the soundboard panel that is great enough to cause shear stress failure within the earlywood fibers such that the latewood layers are forced up or down to form the ridges that we see and identify as "pressure ridges." Unless the soundboard was ribbed and installed at a nearly oven-dry moisture content -- and, yes, this does happen from time to time but it's not intentional -- it is not likely that your climate could supply enough moisture to create the amount of internal compression required to force the development of a pressure ridge. Quite the opposite. Since compression-crowned soundboards depend on there being enough humidity in the air surrounding the wood to swell the wood fiber and create enough internal compression to form and hold crown I suspect that your major problems will be a nearly complete loss of crown (along with downbearing) and a bunch of opening cracks as the boards dry out. It is, of course, quite possible that these pianos could have arrived in your climate with soundboard compression ridges already developed. (Compression, or pressure, ridges are a malady most often found after a soundboard has been exposed to some high level of humidity for a prolonged period of time. Unless, as noted, the boards were too dry to begin with.) If the compression ridges were already there, you will ultimately find that you have a maze of cracks to contend with. Compression ridges are, by definition, areas of wood in which the wood fiber has been stressed beyond its failure point. The cracks are already there. They are just waiting to open up and become visible as the wood dries out enough to make this possible. -- ddf
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