Transduction and Acoustic Radiator by Kristen Roos

Acoustic Radiator prepared speakers electromagnetic spectrum
Acoustic Radiator by Kristen Roos. © Kristen Roos

Not only is Kristen Roos working with the frequency range audible for human beings, but also many other frequencies and vibrational phenomena are of high importance in his work. He makes different parts of the electromagnetic spectrum perceivable for human beings and often vibrations are translated from one form of appearance to another. Kristen’s work investigates what we would perceive if we had an organ similar to a radio frequency receiver. It connects us to the unseen and unheard world of all these frequencies surrounding us in everyday life. Many of these frequencies are part of the electromagnetic spectrum which  includes for example not only light but also micro-waves, X-rays and radio waves. The frequencies of this electromagnetic radiation are often very high, in the realm of terahertz or even more. By translating these frequencies into different media Kristen makes them audible, and loudspeakers play a central role in this sonification process. His installation Acoustic Radiator (2016) gives us a bewitching impression:

At the core of this installation is a WiFi router. WiFi routers periodically transmit so-called beacon frames to report the presence of a wireless network to possible receivers of that network. This is similar to how a lighthouse is sending out its light signals. The signals sent by this WiFi router are in the 2.4 GHz range. A radio frequency receiver is used to pick up these frequencies. With the help of a modular synthesizer (with a clock divider, VCA’s and ADSR’s) and audio amplifiers the signal of the router is transformed into an electric current, which is sent to three loudspeakers and a subwoofer. Another loudspeaker is placed on the table next to the WiFi router and connected directly to the RF receiver. Asking him about the function of this fourth loudspeaker, Kristen answered me that this allows the visitor to see the movements of the mechanism which is the same as the speakers that vibrate the radiators and door.

Kristen Roos Acoustic Radiator
Overview of the set-up for Acoustic Radiator.

The three other loudspeakers are also prepared with a small metal rod, attached to their dust cap (the centre part of their diaphragm). On top of the rod a piece of felt is placed. These prepared loudspeakers are placed in the space, two touching a radiator, the third one placed against a door.  Kristen made this video to explain this translation process from electromagnetic waves radiated by the WiFi routers to audible waves radiated by the loudspeakers:

The loudspeakers in this installation are used as a kind of automised percussion players, since they hit objects such as a door and radiators. But this hitting is done not by a single hit but with many vibrations, causing the radiators and door to vibrate much more variable than it would when just hit once. As Kristen explained me he decided not to use common tactile transducers (which he used for example in his work Ghost Station) but instead developed his own prepared loudspeakers. He had several reasons for this. First of all, the installation consists of all kinds of misused equipment, and therefore a misused loudspeaker seemed to be more at place than a properly used tactile transducer. Also, the making of the sound becomes clearly visible to the audience by the vibrating metal rod. Furthermore, and perhaps most significant, the sound can be more precise and subtle, since the felt-covered metal rod is able to transmit the vibrations on to a very specific small spot of the radiators and door.

prepared speaker metal rod
A loudspeaker prepared with a metal rod and felt is placed next to a radiator. © Kristen Roos
prepared loudspeaker
The third loudspeaker prepared with a metal rod and felt is placed next to a door. © Kristen Roos

For transmitting the low frequencies a subwoofer is hidden under a pile of out of use radiators. These radiators “radiate” the sonic vibrations of the subwoofer, because they will start to vibrate according to the low frequencies produced by the subwoofer.  It is through these combination of loudspeakers—the speaker connected to the RF receiver, the three placed close to radiators and door and the subwoofer—that the signal of the WiFi router is materialised into sound. The title of the installation itself is of course a reference to the old radiators used, but at the same time an acoustic radiator is also another name for a loudspeaker.

subwoofer radiator
A subwoofer is hidden under a pile of radiators. © Kristen Roos

The direct translation from imperceptible frequencies around the audience becomes even more clear by the involvement of their own personal devices radiating electromagnetic frequencies. Entering the room, they can connect their mobile phone to the WiFi router. This will result in some glitches in the sound of the installation happening due to the establishment of a new connection between router and mobile phone.

Transduction by Kristen Roos.
Transduction by Kristen Roos and Dorion Berg. © Kristen Roos & Dorion Berg

In Transduction (2001), an installation developed together with Dorion Berg vibrations are once more the point of departure. Eight towers with each a dismantled monitor, a reversed drum skin filled with water and a loudspeaker are presented in the gallery space. The original electric signal is produced by a drum machine—a Yamaha RX7—with eight different outputs. Each of the loudspeaker–drum skin–monitor towers is connected to one of these outputs of the drum machine. This electric signal is translated into two different forms of presentation: in a visual form on the monitor and as audible vibrations of a loudspeaker membrane. The loudspeaker membrane vibrations are transduced into another waveform, namely water waves. The loudspeaker membrane is connected to the reverse drum skin filled with water by a thin fishing line. In this manner, the vibrations of the speaker are picked up by the drum skin and will gently move the water in a wave pattern specific to the vibration frequency. Since the drum skin is placed directly above the monitor, the water waves break the light of the monitor. In this way the different representations of the same signal are meeting again, leaving a mysterious impression of their hidden electrical origins .

transduction dorion roos loudspeaker water drum skin
Each of the eight towers contains a loudspeaker, a monitor and in between a drum skin filled with water. © Kristen Roos and Dorion Berg.
loudspeaker water drum skin
The same electric signal is sent both to the loudspeaker and the monitor.

Fifty years of loudspeakers and ping pong balls

Some objects seem particularly suitable to be used for preparing loudspeakers. The lightness and characteristic sound of ping pong balls might be a reason, why they have been favourable objects for this. Comparing several of these set-ups reveals that—fortunately!—using a similar technology can still result in completely different works.

Loudspeakers ping pong balls
Leser 1 by Manfred Mohr and Jochen Gerz. The loudspeakers and ping pong balls are covered by a large transparent plastic bag. Polyester tube, 19 loudspeakers,  printed transparent plastic bag, 19 moving ping pong balls, electric motor, 180 cm x 45 cm, 1967 Source: © Manfred Mohr and Jochen Herz

As far as I know, the first work using ping pong balls in combination with loudspeakers is Leser 1 (1967) by Manfred Mohr, who created the audio sculpture, and Jochen Gerz, who wrote the text for this installation. This  tower contains 19 loudspeakers, each prepared with a single ping pong ball and was exhibited for the first time in 1968 in Paris. The audience can press a foot pedal to turn the installation on for a minute. Three different frequencies are then played through the loudspeakers and causing the ping pong balls to move away from the loudspeaker membranes and hit the plastic bag (see also the scheme at the end of this post). The ping pong balls are alternating between striking the plastic bag and the loudspeaker membrane and the combination of 19 ping pong balls making this movement produces a noisy sound. Together with the text printed on the big plastic bag and a random letter printed on each ping pong ball the whole installation seems to make an attempt to speak. The text itself seems also to be related to the movement of the ping pong balls: the big letters in the middle read: “Auf Flüchtlinge wird [ge]schossen”, which could be translated as “shoot the people fleeing”. Manfred Mohr explained me, that this text refers to the fact that at that time the East German police had the order to shoot the people fleeing to West Germany.

In Music for Pure Waves, Bass Drums and Acoustic Pendulums (1980) Alvin Lucier uses four bass drums and places them in front of four loudspeakers. A low sinus sweep is played through these loudspeakers and the membranes of the bass drums start to vibrate, according to their resonance to the frequency of the sinus wave. In front of each drum a ping pong ball is hanging from the ceiling, just touching the drum head. The vibrations of the skin push the ping pong ball away from the drum. Depending of the moment of hitting the drum, when the ball falls back, as well as the direction and amount of vibrations of the drum head, the ping pong ball will be pushed away next time with more or less force. Although the set-up seems to be four times the same, the results of the small differences in material of bass drum, loudspeaker and ping pong ball can be clearly perceived in the movement of the ping pong balls and the resulting sound. The shape of the ping pong balls reminds me of the head of a drum stick, and these drums seem mysteriously “played” by the ping pong balls.

Christian Skjødt uses 16 loudspeakers and an equal amount of ping pong balls in Inclinations (2016). Here again each loudspeaker with ping pong ball combination creates its own rhythm, but due to the ping pong balls moving in upwards direction they fall down much faster than in Lucier’s set-up. This causes a constantly changing, soft and noisy rumbling. Christian is not using any other material such as a plastic bag or drums. Since the frequencies played through the loudspeakers are too low for humans to be heard, all sound is produced by the collisions of ping pong balls and loudspeaker membranes. The minimal visual quality of this installation underlines the focus on these sonic events.

loudspeakers ping pong balls
The three different relationships between ping pong balls and loudspeakers, from left to right: In Leser 1 the ping pong ball hits the loudspeaker and the transparent plastic bag. In Music for Music for Pure Waves, Bass Drums and Acoustic Pendulums the loudspeaker just hits the drums. In Inclinations the ping pong ball is placed directly on the loudspeaker.

After I finished this post on loudspeakers and ping pong balls, Ricardo Arias brought the piece PingRoll (1997) by Manuel Rocha Iturbide to my attention:

And João Ricardo mentioned Kugel-Percussion (2006) by Peter Vogel to me:

loudspeaker ping pong ball
Kugel-Percussion by Peter Vogel, with one ping pong ball and one loudspeaker © Peter Vogel

And another addition: When preparing my text on Sound in a Jar I bumped into another piece of Ronald Boersen, using loudspeakers and ping pong balls, called talk to me… . The ping pong balls are hanging in front of a tam-tam . You talk into a microphone and see and hear your speech reflected in the movement of the ping pong balls. To achieve this, the voice is processed in the computer, attenuating resonating quality in the speech, that maximises the response of the resonating frequencies of the tam-tam. This sound is than diffused through a tactile transducer attached to the tam-tam. The ping pong balls start to move due to the tam-tam vibrations, creating sounds themselves as soon as they hit the tam-tam:

p. 155 desafinado by Wolfgang Heiniger

A short fragment of desafinado (2005) for soprano saxophone, snare drum and a loudspeaker inside the snare drum, composed by Wolfgang Heiniger, performed by Marcus Weiss: