The parametric loudspeaker, commonly referred to as an “audio spotlight” (from the name of the product that popularized the technology), has been one of the most discussed audio innovations in recent years. It is based on the principle of acoustic heterodyning, in which ultrasound is employed to project a modulated sound signal in a focused beam, which then demodulates into audible sound when it encounters an acoustically reflective surface. When the listener’s ears are positioned in the path of the beam, it produces the illusion of hearing a sound originating from the proximity of the listener’s head (as if wearing an invisible pair of headphones). When the listener is positioned outside of the beam and the speaker is pointed at a reflective surface, the sound source appears as if it were located at the point of reflection (as occurs optically in film and video projections). The complexity of parametric loudspeaker technology and the cost of the first commercially available products has made it challenging for DIY audio circles and artists to experiment with this principle, but recently several relatively low cost and open source variants have appeared. Adam Donovan is a sound artist who has been engaged in this field of research since 2002. He has developed a series of robotic loudspeakers that he refers to as “psychophysics machines”, which he uses to create non-standard listening experiences. His Multiplexing Tautophone features a parametric speaker mounted on a robotic tripod that is able to rotate on two independent axes at a speed of up to 500 RPM. When employed in a large enough space, the phantom source (the focal point of the acoustic lens) moves around the space at speeds with a magnitude comparable to the speed of sound, generating psychoacoustic effects that are hard to imagine without experiencing the work in person. Matteo Marangoni

 

Multiplexing Tautophone