I have maintained literally hundreds of pianos over the last four decades whose soundboards have had little pooched-up lines along some of the glue joints. Many piano owners see these little pushed-up places, and they become very concerned; they think the piano is ruined, that it’s a lemon, that the warranty should declare the board defective and replace it….

But nothing could be further from the truth. Here’s what I wrote to a client that bought a wonderful 20-year-old Yamaha C3 from us, and discovered the dreaded little raised glue joints on his soundboard:

Hello—that, my friend, is a pressure ridge. It’s been in this board since I first saw the piano, years ago. It has absolutely no effect on the sound or the value of the instrument. A huge percentage of pianos, Steinways or whatever brand, sometimes develop these. It’s where one of the glue joints on the soundboard panel is pressed against its neighbor as the board goes through its normal cycle of swelling and abating; a little ridge is formed. There is absolutely nothing to be done, and no effect on the touch or the tone. I have bought and sold many pianos with pressure ridges, and many of my beautiful custom-restored Steinways have them.
No problem. Please enjoy that wonderful piano—and the holiday…

And here’s what the Mothership, Yamaha Corp., has to say:

“The issue of soundboard ridges and cracks is often misunderstood. At Yamaha, we recognize the fact that since the soundboard is made out of wood,it will always be subject to the effects of fluctuations in relative humidity (RH). In order to produce Yamaha’s signature tone, the design of the soundboard incorporates pressure and tension; this means that at times of high RH, it is quite possible for the board to exhibit pressure ridges. At times of extremely low RH, it is also quite possible for cracks, or separations between panels, to appear. These phenomena are indicators of good quality wood in your soundboard,that reacts as it should to these RH conditions.
As long as the panels do not separate from the ribs on the back side of the soundboard, which may cause buzzing and other objectionable sounds, the overall quality of tone will not be affected. Since the function of the soundboard is not compromised, there is no defect.”
Yamaha North America

So: those of you who discover a pressure ridge in your precious piano: rest easy. It’s no problem.