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Inverted Piano Action

  1. May 6, 2015 #1
    Hello!

    I have a question about grand piano action design. As a quick primer, the way a piano works is basically that each key is a lever mounted on a fulcrum, so when a player presses a key, the other end of that lever rises. A hammer is attached to the other end of the key, and when that end rises, the hammer swings up and hits a string, which produces a sound.

    On all grand pianos, as far as I can tell, the other end of the key levers are very short, so the hammer is positioned near the player. The length of the lever is approximately equal on both sides of the fulcrum (the player presses the key, and the other end which the player does not press is also about as long as the key). What I am wondering is:

    1. Suppose someone made a piano with much longer key levers so that the hammers could be positioned in the back of the piano, but leaving the fulcrum where it was. What effect would that have on the player? They would be pushing the short end of a lever (the key) with a much longer back end, which would seem to me to be more unwieldily (and is perhaps why pianos aren't designed like this), but it's been a while since I've taken physics and I'm not quite sure.

    2. Suppose someone made a piano with much longer key levers so that the hammers could be positioned in the back of the piano, and also moved the fulcrums so now the player is pushing on a very long key to move the relatively short other end of the lever. What effect would that have on the player? It would seem to me that it could result in louder song (longer lever arm=more torque=hammer hits the string harder), but again, I'm rusty and not quite sure.
     
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  3. May 6, 2015 #2

    CWatters

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    I think the main effect would be on the increased force with which the key has to be pressed to lift the hammer. If the hammer weighs the same but is 10 times longer the required key force would be 10 times higher. In addition the speed with which the hammer hits the string would be about 10 times faster. I think it would be very hard to play softly and consistently. You would have to apply a larger force but slower to keep the hammer speed the same.

    No the torque would be the same because the ratio of key length to hammer length would still be roughly 1:1. There might be an issue with the moment of inertia of the keys making it harder to play fast. I suppose the weight of the key and hammer arms could be reduced to keep the moment of inertia the same but I think they are already quite light. Might be a problem finding light enough materials to make them 10 times longer but just as stiff?
     
  4. May 6, 2015 #3

    Svein

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    I have owned such a piano. It was incredibly easy to play, since you could control everything from piano to forte just by using your fingers.
     
  5. May 7, 2015 #4
    Svein: That's really interesting. Do you happen to remember if that piano was a certain brand/type/something searchable? I'd love to be able to look up pianos like that.

    If it was easier to play, I wonder why it wouldn't be more common? Did you notice any disadvantages? Maybe it was harder to control fine details since your dynamic range was so much wider?

    CWatters: If changing the system so the key side of the lever were much shorter would make it harder to play (due to more force), then I'd think that, if the system were instead changed so that the key side of the lever were much longer than the other side, it would be easier to play (needing less force, like Svein described above). Or am I forgetting something?
     
  6. May 7, 2015 #5
    Keep in mind also the vertical displacement it takes to push the key. On the string side you want to keep a certain safe distance from the string when not being played. If the fulcrum is very far back into the piano that would mean you would have to push down the key very far.
     
  7. May 7, 2015 #6

    Svein

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    Well, that kind of piano you are not likely to get anymore. It was a "player piano", which meant that it could play those perforated paper rolls that were popular around 1920. Due to the player mechanism, the piano was very deep, with long levers. Also (and here I am speculating) the player mechanism could not provide much force, so the playing action had to be light and responsive.

    The brand of that particular piano was Behning. It was very large and heavy - about 750kg (the same mass as three modern pianos).
     
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