Hi list, Stan Kroeker wrote: >Not quite sure I fully understand what is going on when humidity changes >cause pitch fluctuation. Ya, ya...I know...humidity goes up, soundboard >swells, crown rises, string tensions increase...but... it is always the >lowest tenor strings (10-15 unisons?) which are affected disproportionally >to the rest of the scale . . . . . . . . . Weird things often happen on either >side of the treble (strut) break as well. > >Some pianos exhibit extraordinary pitch swings . . . . Is there more to >this phenomenon than the soundboard swells or shrinks? Yes there is! The lower tenor and either side of the treble (strut) break are, in many pianos, designed with string lengths which produce wide variations in the percentage of breaking strain when at pitch. This will result in the pitch deviating more in response to soundboard movement when humidity changes. Furthure, if the downbearing angle lacks uniformity these pitch variation will be more pronounced. We have measured over fifty different piano scales over the years. There is a definite relationship between the overall deviation in the percentage of breaking strain, and the tuning stabilitiy. While other factors also have an influence, the most carefully manufactured piano with a large deviation of breaking strain will always exhibit poor tuning stability, eg. Yamaha U3. The Yamaha C7F, which has much less breaking strain deviation when compared to previous models, has much improved tuning stability. A comparison of the scales of a Kawai KG6 and a Steinway model D will show that the Kawai has apprximately 10% less deviation in the percentage of breaking strain accross the scale. A well rebuilt KG6 will always exhibit superior tuning stability to a well rebuilt model D. It is all a matter of scale. Regards to all, Ron E. Overs Email: ron@overspianos.com.au Website: www.overspianos.com.au
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