The Ultrasound installation consists of two facing parabolic mirrors placed about 20 meters (the longer the better) from each other. In the focal point of each mirror is a speaker and a small LED-light. The very high pitched sine wave sound played through the speakers create a kind of sound beam between the mirrors. In optimal accoustic conditions the sound is heard only between the mirrors, not elsewhere in the space.

The pitch of the sound coming out of one of the speakers is about 16.000 Hz while the pitch of the sound coming out of the other speaker is moving randomly between 12.000 Hz and 20.000 Hz. This random movement of the pitch is caused by a geiger meter measuring the constantly changing background radiation of the air in the exhibition space.

Besides the sounds coming from the speakers a spectator standing between the mirrors can hear a third sound which frequency is the difference of the two above mentioned frequencies. This modulation sound is coming from all around, its source cannot be defined. This phenomenon together with the two other high pitched sounds somewhat distorts the spectators perception of space.

This installation was made in 1996 for Manifesta 1 -biennale in Rotterdam and has appeared at shows in Tampere (1997), London (1997), Stockholm (2000), Frankfurt (2002) and Hasselt (2004). It is part of Kiasma's (Finnish Museum of Contemporary Art) collection.