>Stop me if you've heard this one before, but... >is there any reason why low EMC board ribbing and compression crowning >necessarily go together, or is it an accident of history? Historically, low MC ribbing is the accepted method, but similarly destructive levels of panel compression can be gotten by pressing a less severely dried panel and rib set into a suitably dished caul at a higher MC - if you really want to. >I also gather that it's the low EMC panel assembly which causes most of >the damage. For each assembly EMC, the ceiling EMC (and by correlation >ceiling ambient RH) beyond which compression damage occurs, is set. The >lower the assembly EMC, the lower the maximum ambient RH it can withstand >before damage occurs. The lower the maximum ambient RH, the less headroom >the owner has in controlling the piano's environment Yes, like the maximum sales profit on a speculative rebuild being determined by the purchase price of the carcass. >Again, stop me if you've heard this one before (or send me to the >archives), but in a panel with significant compression ridging but thus >far without the consequent cracking or break-down of rib-board glue >joints, what is the effect on board resonance, you know, the magic tone >disks? Or will the damage to resonance only show up as a result of >board-rib separation, prematurely brought on by the compression damage? If the ridges are obvious, the humidity is high and the soundboard response will probably be as good as it's likely to be for that particular assembly. It's when the humidity is low and those compression ridges recede (whether or not they separate into cracks) that the percussive attack and short sustain of a too flexible low impedance assembly show up first. That's why it's sometimes hard to tell how bad the soundboard is in the summer, and how good it is in the winter. Ron N
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