Because soundboards are large thin wooden panels, they are very susceptible to humidity changes. In areas with large humidity swings (like Minnesota) the soundboard can swell and contract quite a bit with the seasons, taking the tuning up and down with it. In extreme dry conditions, or if the piano is placed in front of a large heat source, it can shrink so much that it will crack. In some cheaper Asian made pianos, the wood isn't always seasoned well enough before manufacture to withstand the North American climate, making it also more susceptible to cracking.
Posted by Dean Diers Piano Service at 12:53 PM CDT
Updated: Wednesday, 26 October 2011 7:09 PM CDT