the soundhats were used by the dancers in one part of the performance piece worldswithin. they consist of a circuit board, a light sensor and a really silly looking headpiece made from a a paper cone with a speaker and flashlight inside, which is mounted on bicycle helmet.
the circuit board contains two oscillators, one with a fixed frequency and another with a frequency that is controlled by the amount of light that falls on the light sensor. when just the right amount of light strikes the sensor, the two oscillators are in tune with one another. the sensors are extremely sensitive though, so it is difficult to tune the oscillators exactly. when they are out of tune they make strange and lovely beating sounds.
if a number of people are in a dark space wearing the soundhats, they can turn on their flashlights and attempt to tune one another from a distance with their flashlight beams. this is a difficult task which requires concentrated listening and great sensitivity to the minute movements of your partner.
the soundhats are rather loud and buzzy sounding, so when a number of them are in a room together they make quite a nice racket. each soundhat is tuned to a different base frequency so that it is possible to track an individual hat in the dark. a very nice effect is created when the only light in a space comes from the soundhats: the flashlights illuminate the faces of their wearers. they can also be used to cast patterns onto the walls of the space.