My work revolves around research and production in the domain of multi-modal perception and new media. The creation of bespoke media environments, including spatial audio setups, interfaces for sound synthesis and composition entails unique attributes, particularly in an artistic context.
- - Experimental Sound Reproduction
- - PCB Prototyping
- - Spatial Composition
This multi-channel sound art installation incorporates up to 16 experimental plasma loudspeakers. The speakers are staged on custom-built glass tables, using laboratory stands creating a minimal lab aesthetic. This type of loudspeaker produces sound through an amplitude modulated high voltage arc with an operating voltage above 30.000 Volts. This arc is an omni-directional sound source with a flat frequency response at higher frequencies and gives a perfect transient response. Hence, it produces a very clear sound. In addition, its point source characteristics allow precise localization in spatial audio environments. Sound is spatially distributed over 16 loudspeakers, which may play together and form a single 3D sound sculpture or each speaker is uncorrelated and perceived as an individual sound source.
Plasmaspeaker
Abstract
This project aimed on the artistic use of plasma speakers in the framework of a multi-channel sound art installation. Main focus was the development of a small series of reliable plasma drivers. In addition, the plasma speakers’ main features, including its unique sound properties as well as its visual appearance, were worked out artistically. This project combines electrical engineering, product design and musical composition.
Introduction
Unlike the mechanical process of a conventional dynamic loudspeaker where a membrane induces vibrations into the air, a plasma speaker’s distinctive feature is ionized gas that acts according to a varying energy input, the audio signal. The varying temperature of this audio-modulated plasma causes the air molecules to expand or to contract, which produces audible sound pressure.
Plasma speakers have unique acoustic properties, because the weight of the plasma is significantly lower than that of a dynamic speaker. As a result, a plasma speaker has a linear frequency response in the higher frequencies and perfect transient response. Most significant is its omni-directional directivity. Commercial products for audiophile home audio systems are available. From a technical point of view, other methods for reproducing high-quality sounds are easier to obtain. Hence, plasma tweeters don’t play an important role in the home entertainment market. However, plasma loudspeakers are very intriguing for artistic use.
Comparison between different methods
Electrostatic discharges can be modulated at audio frequency. Electroacoustic coupling can be achieved by transferring audio-modulated energy into the plasma. Two ways of discharges have been examined: corona discharge and sparks.
Three different driver circuits have been built and compared:
(1) Switching amplifier for driving a tesla coil transformer producing a corona discharge.
(2) Self-oscillating RF circuit built around a vacuum tube and modulation with a transformer, also producing a corona discharge.
(3) audio-modulated chopper circuit, driving a diode-split high-voltage transformer.
1 Tesla Coil Transformer (corona discharge)
Using the tesla coil circuit offers a remarkable volume and gives a relatively stable result regarding durability. However, getting the resonance frequency is crucial for a proper operation. Otherwise the corona collapses quite easily and needs to be ignited manually. Furthermore, in my case, I was not satisfied with the sound quality oft he circuits I used. The circuit was noisy.
2 Vacuum tube (corona discharge)
Vacuum tubes with a tuned circuit for creating an audio-modulated plasma speaker represent the genuine design of the available commercial plasma speakers. The circuit is very reliable and it produces a high quality sound. However, I was not satisfied with its weak sound. Furthermore, the circuits are quite complicated and hazardous due to its high voltage vacuum tube, which produces a dangerous current. A safer method had to be taken into consideration when presenting the work to the public in a museum. The ignition of the corona flame was also unreliable. In addition, the electric components are expensive compared to the other circuits.
3 high voltage transformer (electric sparks)
Using a simple high voltage transformer (diode-split high-voltage transformer) to produce a spark discharge offered the best results for my application. These transformers are easy to obtain. The circuit consists of a simple preamp, a square wave oscillator for the PWM modulation and a MOSFET for driving a diode-split high-voltage transformer. The plasma occurs between the two electrodes as an electric arc. Not only the simplicity of he circuit and the achieved high quality of the sound, but also the aesthetics of this particular electrostatic discharge, the spark, were essential for my decision of using this type of circuit for a multi-channel sound art installation.
Technical Challenges
Electromagnetic interferences and antenna effects introduced massive noise. Grounding, shielding and balanced signaling canceled out the interfering noise. Concurrently, galvanic isolation between the driver and the audio interface was attained by the use of line transformers.
Inductive Coupling
Back EMF was minimized integrating a snubber circuit. Some components, including the transformer, generated a considerably high amount of heat, which could be regulated with heat sinks, and failures could be prevented by the use of heat resistant materials.
Electromechanics
The electrodes were electrically and thermically insulated with borosilicate glass and polytetrafluoroethylene. The diameter and size of the brass electrodes were selected according to tolerable heat dissipation.
Power supply
Each driver was running on a 12V 5A switching power supply and could be remotely turned on or off via a relay. For this a 16-channel relay-controlled power supply was built. The relays were controlled with an Arduino and the switching process was triggered from DAW as MIDI-Messages. In this way, overheating the plasma speakers was prevented. This had an interesting effect on the sound: When switching on a power supply, the respective driver generates the high voltage and the initial ionization of the air causes a significant click. This sound had been incorporated into most of my compositions. However, some technical problems are still present: While using a switching power supply (12V/5A) without a proper current limiting circuit, the current drawn by the transformer exceeded its specifications leading to extreme heat of the wires in the transformer and melting the enamel of the wire causing shortages.
Acoustic properties
Impulse response measurements were made in spat Max/MSP. The lower cutoff frequency is around 1.5 kHz. Frequency and transient response were as expected. Various audio materials were tested. It could be demonstrated that percussive and plucked sounds (guitar, harps or synthetic sounds with sharp attacks) were played back in a highly transparent manner. The precision of high frequency textures was also considerably good.
The precise localization of each single sound source is remarkable. Even when several plasma speakers were put closely together, the speakers were localized separately. Stereo images were perceived unnaturally clear. When all sound sources played in unison, the system worked as a compounded speaker network and created a single large width sound source.
The precise localization of each single sound source is remarkable. Even when several plasma speakers were put closely together, the speakers were localized separately. Stereo images were perceived unnaturally clear. When all sound sources played in unison, the system worked as a compounded speaker network and created a single large width sound source.
ARTISTIC APPROACHES
The plasma of a corona discharge is always close to the resonance coil, because of the electromagnetic field strength. In contrast, when generating sparks as electrical discharge by using the high voltage transformers, the electrodes can be set up in distance from the transformer. This allowed me to stage the plasma speakers on custom built glass-aluminium-steel tables, while the drivers were put on the floor. Black silicon cables transferred the high-voltage signal to the electrodes. Laboratory stands which served as holders for high-voltage electrodes, emphasized the plasma arcs and engendered a minimalist lab aesthetics. Furthermore, the laboratory stands minimized acoustic shadowing effects and the point source directivity was deployed at the best. The visual and acoustic characteristics were convincingly worked out and presented in minimalistic lab aesthetics as a multi-channel sound installation.
Beside the above-mentioned acoustic properties, a plasma speaker offers further qualities for artistic use: generally, the almost immaterial reproduction of sound through light contradicts the human perception. Sound is usually related to a body and mechanical force. In this case only fluctuating light produces a synesthetic effect.
While experimenting with different sounds, I found out that voice worked particularly well when played back through the plasma speakers. Because of the missing fundamental effect, voice can be still recognized as such. However, the phenomenon of creating a sound without a mechanical device but solely by “light”, makes voice very special as compositional material for the installation.
Presentation at klingt gut! Symposium
Various sound concepts had been realized for this installation. For the klingt gut! Symposium in 2017, I emphasized the laboratory aesthetic of electric sparks and the glowing plasma through the use of electric sounding high frequencies. The high voltage sparks together with the electric sounds established a hazardous atmosphere. This coherence made most people belief that the plasma speakers are actually not capable of creating any arbitrary sound within their frequency range.
Live Concert Presentation at GEDOK
In 2018, the system was used for a live concert, presenting compositions by sound artist Sabine Schäfer. For the presentation of the electroacoustic composition „SolarSonical Insects“, the plasma speakers were extended through a quadrophonic PA system and a subwoofer and complemented musically with the performance of a recorder player (Carolin E. Fischer). With this hybrid multi-channel sound system, a spectral and spatial structure was created, corresponding to its original compositional structure. The prominent and filigree texture of the high frequency insect voices in the beginning were played back solely through the plasma speakers, using the system’s unique spatial characteristics and its localizability. During the course of the composition, the sound was gradually distributed through conventional loud speakers to fill the audience space completely, while the musician playing the recorder supported the whole process.
CONCLUSION AND FUTURE DIRECTION
The acoustic properties of the plasma speakers were successfully worked out. Especially the use of a high number of speakers, creating a cluster, gave me the possibility of creating unique sound effects and using unconventional spatialisation techniques. The speakers were placed in the center of a room. This sculptural arrangement made it possible to walk around the installation, which is an interesting alternative to conventional speaker configuration in ring or dome structure. The volume of several speakers is loud enough to use the speakers in a concert situation, as the performance at GEDOK demonstrated. A combination with supportive conventional loudspeakers is a good method for hybrid multichannel systems.
I’m currently working with small electret microphones placed close to the speakers, creating feedback-sounds controlled with Max/MSP. With this method, autogenerative harmonic structures in a high frequency range occur, which blends into the acoustic aesthetics of the speakers’ properties.
