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.