As your Piano Tuner Wilmington DE , I am occasionally asked about “Expanded Octave Tuning.” This post is a continuation of the explanation which was begun in our last blog post. In that post, some basic information about waves and overtones were given as background for the explanation in this post. The following is an explanation that may help with your understanding of the complexity of tuning a piano.
Our previous post explained how a vibrating piano string has overtones or partials. The wavelength of each partial is determined by the endpoints of each string, because the end-points are secured and cannot move. In the simplest case, the string has two segments that are vibrating in each of the two halves of the string. The pitch of this first overtone is typically one octave above the fundamental, except in pianos.
The reason pianos are different is that the strings are thicker, are relatively rigid, and are at high tension. As a result, the strings do not flex exactly at the endpoint. The overtones, then are actually higher than when the string is flexible enough to vibrate all the way to the endpoint, since the string is functionally shorter due to its rigidity. As a result, if a piano string is tuned exactly to the octave below, the overtones do not line up, and the string sounds flat. The piano tuner compensates by tuning the octaves slightly expanded, so that the overtones sound more in tune.
The question, often, is how does the tuner know how wide to tune each octave? The answer is that he/she listens and tunes the octave to where it sounds best. This is usually done by tuning the piano string a little too high, then a little too low, and then returning it to the middle where it sounds best. Because each interval is always a little out of tune, the piano tuner must always use this technique to find out the optimal interval.
If you have other questions about your piano, please let us know. We are your Wilmington DE piano tuning professionals, serving Delaware, Pennsylvania, eastern shore Maryland, and southern New Jersey.