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How do I build an electro magnet strong enough to vibrate piano strings?

  1. May 28, 2012 #1
    I would like to build an electro magnet capable of causing piano strings to vibrate without the strings being struck first. As long as the hammers are up, the strings would vibrate on their own accord.
    An E-bow, used by guitarist for the same purpose, will (sort of) work on a limited range on the piano - but on only one note at a time. I would like to build something that can be hung inside the piano, close to the strings, that covers a wide range of notes. Hopefully I would be able to silently depress the keys, lifting hammers on those keys only, and thus creating an infinitely sustained piano sound, but without the attack the hammer gives. Thanks!
  2. jcsd
  3. May 28, 2012 #2


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    A normal loudspeaker will do this, especially if 'hard mounted' to the piano frame.
  4. May 28, 2012 #3
    Hi - thanks for writing. Please excuse my ignorance, as I know nothing of physics. Would a speaker create this effect w/o producing any noise itself? Is there something inherent about a loud speaker that, if attached to the bottom of the piano sound board, would cause the strings to vibrate enough to produce sound themselves?
  5. May 28, 2012 #4


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    Sound is vibration. The speaker will vibrate, pushing a column of air that will also vibrate. Connecting it to the sound board will just force the strings to vibrate too.
  6. May 28, 2012 #5


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    @OP: have you studied the construction of Hammond organs? There is no sense in re-inventing the wheel when there is very old and well-tested technology that can already do what you want.
  7. Jun 6, 2012 #6
    I made this in 1981, showed it to Fernandes and tom sholz, and was told it had zero marketability.

    A few years later, fernandes comes out with "the sustainer'.

    30 years later, many big name guitarists have at least one "sustaining axe" in thier collection.

    I came up with this one day when I pushed down the tremolo bar (way down) on a kramer beretta guitar in a room lit by only one flourescent light and saw the string and speaker cone vibrating in synch. while wondering how I can get feel of standing in front of a cranked 4x12 cabinet while using a headphone amp.

    Maniac music makes a sustainiac like the sustainer but they have an older model that is a tactile transducer that mounted to the headstock of the guitar.

    I believe a tactile transducer attached to the soundboard of a piano could get you what you want to excite the strings but I'm not sure a mic. would be best for being the source of the signal you send to the transducer.
  8. Jun 20, 2012 #7
    There are many patents of devices that excite piano strings to vibrate but none that will cause feedback the way a "sustainer" circuit can.
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