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.

Points of Contact by Erfan Abdi

Erfan Abdi in the bird cage, performing Points of Contact at STEIM.
Erfan Abdi in the bird cage, performing Points of Contact at STEIM. © Erfan Abdi

Big eyes as contact microphones, a bird cage as a loudspeaker, and two double spring objects of which again one functions as a loudspeaker and the other as a loudspeaker: this is the inventive set-up Erfan Abdi uses for his performance Points of Contact (2017). Erfan himself seems to be a bird, placed in the cage to perform for us, gently trying to break out by touching the bars with his metal eyes.

The sounds during the performance are created by different combinations of the same set-up: both amplification as well as feedback through the contact microphones and tactile transducers are used. By using additional long springs the different elements can be connected to each other. To give an example of one of the many possibilities for doing all kinds of physical signal processing with this set-up: a signal of the big eyes contact microphones is sounding through the bird cage transducer, and since both are touching each other a feedback loop occurs (1 in the scheme below). The bird cage is also connected with a spring (2) to the double springs with a contact microphone (3). This is amplified through the transducer attached to two double springs (4). This is fed back again to the double springs with a contact microphone (5) by connecting the springs with the help of again an additional spring. The sound of all contact microphones is also amplified by the two main loudspeakers in the hall (the PA system) (6).

transducer exciter contact mike microphone Erfan Abdi
Set-up scheme for Points of Contact by Erfan Abdi, see the description above for a detailed explanation.

What makes this set-up so versatile for producing all kinds of different sounds, is that the two feedback loops can both be combined, influence each other but also broken up again (the first feedback loop are the contact microphone eyes and bird cage transducer, and the second the springs contact microphone and springs transducer). Take away, for example, the spring in between the two double springs—(5) in the scheme above—and the double springs become a spring reverb for the sound produced by the bird cage feedback. The whole set-up is constructed in search for fragility and inaccuracy in response to the feedback signal. For this reason, the two contact microphone springs have been chosen by Erfan because their frequency response is slightly different: this results in a modulating feedback sound instead of a feedback on one constant pitch.

The two contact microphone eyes
The two contact microphones are enlarged by small metal plates so they can touch several bars of the bird cage at once. © Erfan Abdi

For the same reason the contact microphones eyes are made by simple piezo disks placed on round metal plates: this gives the possibility to touch the bird cage at two or three bars. As Erfan explained me, when there is just one point of contact between the contact microphone eye and a bird cage bar the feedback tends to be especially strong on the fundamental frequency of the pitch. But as soon as you touch two or three of the bird cage bars, more partials are added to the sound. And by using two contact microphone eyes they also start to modulate each other. The placement of the contact microphone below the  two springs is again aiming for a richer and less stable sound: instead of having just a single point of contact, the whole disk is touching as much as possible of the surface of both springs.

The contact microphone beneath the springs. © Erfan Abdi
The contact microphone beneath the springs. © Erfan Abdi
The contact microphone beneath the springs. exciter body shaker
The tactile transducer underneath the two other springs. © Erfan Abdi
The tactile transducer bird cage exciter body shaker
The tactile transducer attached to the bird cage. © Erfan Abdi

Erfan uses the music software Reason to do some processing of the feedback. Basically it provides a compressor, a delay line and an amplitude follower. The amplitude follower is used for modulating the delay time, so as soon as one frequency gets too loud, the delay is changed, and the frequency of the feedback will also change. The connections between the different parts of the set-up—which contact microphone is connected to which transducer etcetera—is controlled live by Erfan with a small MIDI controller.

During the performance Erfan is sitting in the cage, an intriguing image for a music performance. The movements of his head towards the thin cage bars seem to underline the scenery of a bird locked in against his will. But it is with the resulting sounds that this bird seems to be able to leave the cage: the variety of sounds not only enlarge the musical possibilities of this set-up, but also give the impression that the music can sonically fly away from the cage. The bird might seem to be locked in visually but sonically it is free to come and go.

Below you can view some short fragments of Erfan Abdi performing Points of Contact at STEIM in Amsterdam, and listening to a recording of a performance excerpt. And if you are close to The Hague: Erfan performs a new version of this piece tomorrow (Thursday 10th of October) at Ephémère at Studio LOOS.

Vestiges of Discomposition and other works by Simon Whetham

loudspeaker earth water Simon Whetham
Loudspeaker covered with earth during Simon Whetham’s performance Vestiges of Discomposition. © Simon Whetham

Before Simon Whetham starts his performance, he asks you to close your eyes. However, I could not withstand to open my eyes briefly once in a while. I saw Simon walking around slowly, holding a cymbal in his hands. A tactile transducer was attached to the cymbal (Simon uses Dayton transducers, often also called exciters. If you want to know more, about what kind of microphones and loudspeakers he is using, have a look at the very detailed equipment list on his website). Larger sounds were diffused by a tactile transducer attached to the big metal ventilation system on the ceiling, resonating in different ways depending on the frequencies diffused by the tactile transducer.

tactile transducer ventilation system
The tactile transducer attached to the ventilation system. © Simon Whetham
Simon Whetham object tactile transducer
Simon Whetham is carrying an object with a tactile transducer attached to it through the audience. © Simon Whetham.

Every performance space is different of course, as are the objects you might find in such a space, so I asked Simon how he prepares for these performances. He answered me, that besides being experienced enough now to often know already what object might sound good, “banging and knocking on objects to test their resonance and which part is more resonant is essential. Also when setting up I will place objects in various parts of the room to test how each one works in the space, for distance and if they will even vibrate against another resonant object. But then this can change during the performance as I often have no control over where people sit!” And some of his favourite objects, such as the cymbal, just travel with him.

cymbal tactile transducer Simon Whetham
Simon Whetham holding a cymbal with a tactile transducer attached to it during the blurred edges festival 2016. © Simon Whetham.

As an input Simon uses pre-recorded sounds and recordings made in the performance space itself, but also produces many sounds live. For creating live sounds he often uses a small loudspeaker cone,“I also started working with an open speaker as a sound source, either by playing audible sounds through it and then channeling them around the room, or using inaudible low frequency recordings and placing objects inside the speaker. I like this approach as field recorded low frequencies are often unpredictable in their volume level, creating an erratic ‘rhythm’ with the objects in the speaker or even throwing them out.”

aluminium foil loudspeaker Simon Whetham
A loudspeaker cone prepared with broken glass. © Simon Whetham. Picture by Michel Pennec of humus in Lausanne.

As a result of sending the same recorded sound to the differently prepared loudspeakers in space, there are now several representations in the room: one is the sound of the loudspeaker cone covered with, for example, broken glass or stones, the other ones are very similar sounds somewhere else in the space, but filtered by the spectral characteristics of this object. You hear beautiful reminiscences of sounds of scraping stones, scratching metal, or the electric noise made by a ventilation system. But all of them are surrounded by a sonic aura, which makes them less recognisable, transforming them into more imaginary sounds, not related to any existing things. Listening to a recording can of course never reproduce such a performance, but it might give you at least an impression of what kinds of sounds were used:

In contrast, in Everyday Emanations (Dead End) (2017) the sound source is more easily recognisable and plenty of visual cues reveal the source of the sound. Once again, Simon uses tactile transducers, this time attached to damaged car parts. He recorded sounds of traffic inside objects such as pipes, bottles and cans in the streets of Nakanojo (Japan) and these are played through the tactile transducers. Or in Simon’s words: “So ‘dead’ cars would play the sounds of ‘live’ ones.” This time your eyes should not be shut, since car lamps are used to light the space, turning on and off according to the volume of the sound.

An even more direct examination of the physicality of sounds occurs when Simon uses loudspeakers for creating physical marks. The visuality of the performance—completely absent during the first performance I discussed—plays a crucial role now. Simon mentions the book Lines: A Brief History by Tim Ingold to explain more about these works: “Ingold describes two classifications of lines – threads and traces. I was led to consider traces of sound, or of action that makes sound. This ranged from retracing grooves cut into metal objects by the process of twine production, to actually creating physical traces of sounds, to be displayed as visual representations.” In Trace of Water (2016) several metal wires are attached to a very small loudspeaker. A recording of cascading stream water in Wongol (South Korea) is carrying the loudspeaker through the sand, literally leaving its traces in the sand:

Another work using also the sounds of cascades is the very poetic Vestiges of Discomposition (2016), developed on Mount Tsukuba in Japan. Simon used hydrophones to supply a live sound feed, “carefully positioning it to pick up the most energy from the flow. When transduced to sound through a speaker, this energy manifests itself as a low frequency that is unheard by human ears, but creates a strong movement in the speaker itself.” He now fills the different loudspeakers with earth and water, recreating the landscape the loudspeakers are placed in. “These ‘landforms’ mark every point where the stream makes more audible sound above the water, therefore acting as listening stations.”

In Trace of the Storm (2017), created of the Open Arts Project in Busan (South Korea) a recording of a storm is played through two loudspeakers. One of them is a loudspeaker attached to the wood of a painting, the other one is a speaker cone filled with Korean ink, and producing a similar painting as the first one. “The sound continues to play through both pieces, but is heard in two different ways. The picture filters out low frequencies so you hear more detail, whereas the open speaker is almost inaudible, but creates another ‘drawing’.” This results in what could be called an action painting by a loudspeaker. In Simon Whetham’s works the microphones and loudspeakers are not only transducing between air and electricity, but they translate between all kinds of movements and sounds.

The trace of the storm by Simon Whetham
The trace of the storm by Simon Whetham: one finished painting and one in the process of making. © Simon Whetham.

Touche Nature by I-lly Cheng

We Spoke plays Touche Nature by I-lly Cheng
We Spoke plays Touche Nature by I-lly Cheng. © I-lly Cheng.

Vibrations of loudspeaker membranes cause air pressure waves, which our hearing system perceive as sound. As long as they are travelling through the air, these sound waves stay invisible to human beings. But as Ernst Chladni described in his book Entdeckungen über die Theorie des Klanges already in 1787, sound can be visualised by bowing a surface lightly covered with sand. So-called Chladni patterns are produced in this way. In her piece Touche Nature (2017) I-lly Cheng creates a phenomenon similar to Chladni patterns by placing transparent bowls filled with water on loudspeakers. The sound waves are visualised as water waves:

A bowl filled with water is placed upon a big loudspeaker in I-lly Cheng's piece Touche Nature
A bowl filled with water is placed upon a big loudspeaker in I-lly Cheng’s piece Touche Nature. © I-lly Cheng

A contact microphone is attached to the bowl and amplifies the bowl itself and the water movements in the bowl. Four percussionists each play a bowl filled with 1000 ml of water. During the performance the percussionists produce sounds by moving the water with their hands, rubbing the bowl, throwing stones in the bowl or pouring more water in the bowls. These sounds are all picked up by the contact microphones and then amplified  through the PA system. The water sound itself is also picked up by four condenser microphones and amplified directly through the loudspeakers in the hall.

The first page of the score of Touche Nature by I-lly Cheng.
The first page of the score of Touche Nature by I-lly Cheng (for the attentive reader: in the original version 500 ml water was used, but this was corrected to 1000 ml). © I-lly Cheng

As the first page of the score shows, the sound is processed with a pitch shift effect in the computer and there is also some feedback used. The feedback is created by sending the signal of the contact microphones back to the four loudspeakers underneath the bowls. There is no direct feedback happening though, but a pair of two loudspeakers and two microphones is together producing one big feedback loop.  The sound picked up by the contact microphone of player 1 is sent to the loudspeaker of player 3, which is then picked up by the contact microphone of player 3, creating a feedback loop by sending it to the loudspeaker of player 1. The same feedback is created between player 2 and 4.

An overview of the loudspeakers and contact microphones used in Touche Nature. The four condenser microphones used for direct amplification of the water sounds are not on the picture.
An overview of the loudspeakers and contact microphones used in Touche Nature. The four condenser microphones used for direct amplification of the water sounds are not on this picture. © I-lly Cheng

You can hear different kind of effects, including some feedback, at the very beginning of the piece, performed here by We Spoke:

During the piece I-lly explores the sonic world between natural water sounds and more abstract percussive rhythms. At the end of this fragment some pre-produced sounds are played through the loudspeakers, creating big movements in the water. These movements can not only be seen but the water sound caused by these movements is amplified through the condenser microphones. The loudspeakers seem to become liquid themselves: