The Electromagnetically-Prepared Piano consists of 4 main components:
1) The electromagnet units
2) The rack and electromagnet suspension system
3) A 12 channel amplifier system
4) An audio interface, allowing for the output of 12 discrete channels of audio
An explanation of the function of each of these components can be found below. For specifics about the components themselves, see the Specs section.
As mentioned on the Basic Principles page, each electromagnet unit consists of the electromagnet itself plus two permanent magnets glued to its sides. The permanent magnets are arranged such that they are of opposite polarity – in other words if they were brought together without being turned over or rotated, they would repel.
The rack is a bar that lays over the piano frame, secured in place by velcro straps. Attached to this are twelve brackets designed to hold each electromagnet in place over its designated piano strings. The rack and bracket system allows each electromagnet to be placed anywhere over the width of the piano. The brackets function as a suspension system, allowing for precise adjustment of the distance, or gap, between the bottom of the electromagnet and the piano strings. This distance is critical – if the gap is too large, the magnetic field won’t be strong enough to vibrate the strings adequately. If the gap is too small, the strings will hit the electromagnet. This makes an interesting sound, but is difficult to control.
The 12 channel amplifier system is required to boost the 12 audio signals to levels sufficient for driving the electromagnets. The stronger the signal, the louder the response from the string. BUT – if the signal is too strong the coil inside the electromagnet will melt. (Incidentally, when the insides of an electromagnet melt over a string it makes a really beautiful sound, but electromagnets are rather expensive so not recommended unless you have a really big grant…).
The audio interface simply allows for control over 12 discrete channels of audio. Technically it would be possible to drive the entire system from an iPod or some other stereo output device, but it’s much nicer to be able to independently manipulate the signal sent to each electromagnet.