One of the strangest thing I’ve looked at recently is a Yamaha Silent Piano. On paper it sounds a bit weird but here is the idea.
Take a perfectly good upright piano (actually a very good one) and then add a digital piano as well. The clever bit is that you can mechanically disable the normal piano so that the hammers do not strike the strings but a series of optical sensors under the keys still determine which notes have been played. You then plug in a pair of stereo headphones and practice away without disturbing anyone – genius…
As a bit of a nerd I was quite impressed by the optical detector system that determines which notes have been played and at what velocity. This is done by two beams per key (2 x 88). As a wired system would need two wires per beam this has been reduced by using optical fibres. This allows multiple beams to be derived from a single transmitter and that multiple beams can be received by a single receiver, thus reducing the electronics. The whole lot is arranged as a matrix that is being scanned at regular intervals fast enough to be able determine which of the keys have been pressed.
As each key has to cut two beams then it is possible to calculate the speed the key is travelling by measuring the time taken between the beams being cut. On the one I looked at there was a small brass vane on the bottom of each key positioned so it cuts both beams.
The bit that got me was that with headphones on and the piano in silent mode the brain links the clunk of the disabled hammer with the sound in the phones and projects the sound “into” the piano making the experience of playing very realistic indeed.