This is a neat little video of the mechanism of a grand piano that came across my path. It’s worth a watch to see the inside of a piano virtually pulled apart and to see what the dimensions of the pieces are. It’s amazing how intricate these creatures are! That soft pedal that I love so much only moves the hammers 7% of an inch. Wait till you hear what else it does!
When the hammers hit 2 instead of 3 strings, the tone is sweeter for a few reasons. A lesser used part of the felt strikes the strings, creating a softer tone. This accounts for the entirety of tone quality change in the lowest register of the piano, where there is only one string per note. In the middle range, another factor is at work. When one of the three strings is not struck, it doesn’t sit there with cold-hearted resentment but vibrates in sympathy. This changes the proportions of the of the two phases to the decay of a piano note: the immediate sound and the resonance. When two of the three strings are struck, we reach the resonance phase much sooner. This is the sweet, singing sound that isn’t as strident as the initial sound following the attack. The physics of how this happens is so cool but it should be the subject of a separate blog post.
It should be added that the soft pedal on an upright piano does not shift the hammers from side to side, rather it moves the hammers slightly closer to the strings, causing them to strike the strings more slowly. This reduces the volume but doesn’t change the ratio of immediate sound to resonant sound.
The sustain pedal, the most commonly used one, is capable of enriching the sound beyond what you might realize. I’ll describe two situations to you. In one situation the pianist holds down a chord with no use of the damper pedal. The only strings that resonate are the ones that were struck by the hammers. Another way to do this is to hold down the same notes, but add the damper pedal. When all of the strings on the piano are available to vibrate sympathetically, the upper partials of the notes the pianist is playing are free to nuance the chord. In other words, the first situation is the default, concise way to express the chord. The second is richer, but requires more attention so you don’t get a muddy sound if you add more notes. The nerds among us can read more about this on PubMed.
This brings us to the middle pedal. The geeky pedal. It’s super useful for one specific thing, but other than that it doesn’t have much of a purpose in life. It allows for selective sustaining. There are so many possible creative uses for this pedal, that it’s a shame it isn’t built into all pianos, because then it might be used more often in the body of compositions for piano. Theoretically, one could get the best of both worlds from the situations I described above by silently depressing the keys of the upper partials of the chord you want to play while ensuring that other notes you may want to add will not clutter up the sound. If this is bordering on impracticality to get the richest sound, then so be it. Some of us will spring for that extra clean and deep sound. More commonly the middle pedal will be used to give extra freedom around a pedal tone. If you want a pedal tone to be resounding for a long time while you can use any manner of piquant or staccato otes around it and not have to worry about them cluttering up the sound, then that’s the only way to do it. It really opens up harmonic possibilities. Granted, I don’t use it often in my playing, nor can I think of anyone who does. We tend to use bass players instead!