For a few days now, my upright piano has started having the following issue: when playing a note, upon releasing the key, a resonance of the same frequency can be heard.
The problem seems to have arisen overnight; this resonance is audible for about 15 seconds and seems to come from the central part of the soundboard. It occurs with different notes, and it is not caused by any single string (I touched all the strings, repeated the test several times, and the resonance never stopped); I have touched all the internal parts of the piano (pedals, muting felt, keys...) but the resonance continues; I even removed the action immediately after playing the note, and the resonance continues. The resonance does not have an excessive volume, but if the room is silent, it is evident. When playing, it is not audible, as it is overwhelmed by the sound of the strings; the problem only arises when one stops playing.
I suppose it is difficult to find the cause solely from the description, but if you have any suggestions...
I also believe it depends on some damper (generally the bass ones) that is not well aligned, which resonates on certain harmonics. If the piano is old, perhaps it is time to replace the damper felts and adjust them carefully
Great!! As you correctly hypothesized, it was indeed the dampers, and specifically those of the bass register.
The mistake I was making when damping them manually was damping one string at a time, and letting the note resonate until the resonance faded. By trying to damp all the strings of the bass register simultaneously, the annoying resonance finally disappears.
Attention: You must evaluate whether it is just a matter of regulation or if they must be replaced. Their hardening, especially in the wedge ones in the bass, results in poor and imperfect adherence to the strings. Also check the springs.
Thank you very much for the countless tips, it is a true gift to receive all these pointers and advice.
The piano is from the 70s, and the dampers are most likely the originals; I fear they have hardened by now, at least they feel that way to the touch, so it shouldn't be a matter of regulation.
Unfortunately, however, I will be moving abroad shortly and will have to sell the piano, so I doubt I will have the opportunity to attempt replacing the dampers. I am content with having determined the cause of the resonance, which will surely be useful to me with other pianos, and being able to point out the cause of the problem to the buyer.
