As your experienced piano tuner Wilmington DE, Kenneth Keith Piano Services, I frequently see pianos that have one or more piano hammers that strike twice when the key is played only once. The explanation can be useful for all piano owners, because this situation is often mistaken by the pianist as evidence that the piano needs tuning. In our previous blog article, I explained a lot of the background information about double-striking or “bobbling” piano hammers, and I explained the most common cause, “lost motion.” This post is a continuation detailing the second of the four most common causes.
The second most common cause of bobbling piano hammers is poor hammer blow regulation. The piano hammer blow distance is set by the piano action designer, so that the action has the most sensitive feel. A sensitive feel is important, so that the pianist has the greatest possible control over dynamics, so that the music that results is the music that was intended by the pianist. As a piano action wears with use, the sensitivity of the action is gradually reduced. Lost motion and piano hammer blow distance often go hand-in-hand so that the sensitivity of touch is reduced long before a bobbling hammer appears.
Most piano action designs call for the hammer blow distance to be between 1 3/4″ to 1 7/8″, or 46-47 mm. As the felt of the piano hammer rest rail gets compressed with use, the hammer blow distance increases, requiring more force from the pianist in order for the hammers to reach the piano string. If the hammer blow distance increases a great deal, the the action does not complete, causing the rebounding hammer mechanism to strike the top of the jack and be propelled to the string a second time, resulting in a bobbling hammer. The correction is a relatively inexpensive piano repair adjustment, then lost motion is typically regulated in the same visit.
If you have any questions about piano maintenance or function, please be sure to ask us. We are your Wilmington DE piano tuner, and we are always happy to help. We also provide piano tuning in Philadelphia, Eastern Shore MD and Southern New Jersey.