The system entitled Out of control, which we have designed, is a tool for spatial distribution of sonic events, but it is not a sound system in the familiar sense. It goes far beyond the mere distribution of sounds into space. Instead, it contains significant characteristics of a musical instrument. With this undertaking, we are primarily interested in exploring the spatial behaviors of sonic events in extreme situations. The system enables seamless navigation through a space of possibility with different spatial and phonetic representations.

The system distinguishes itself from conventional PA systems in the following ways:

• The system permits extremely fast movements in space, up to the boundary of the physically possible. Depending on the qualities of the original sound material, completely new auditory location effects can come about.
• The rapid movements also lead to a distortion of the sound materials, which in turn gives the spatial movements additional unique qualities.
• The use of electrostatic broadband transducer with their extreme directivity leads to internal sonic spaces and localized listening positions.
• The material characteristics and appearances, which are revealed in the original sounds by these processes, can be made very gradually audible.
• system can be controlled both in real time and through the use of various kinds of predetermined lists or tables.

Technique:
The system is largely defined by movement patterns on the electrostatic transducers (loudspeakers). One peculiarity of such speakers is their extreme directivity. This directivity is a function of the frequency, as depicted in the following figure.

As can be seen in the image, the electrostatic transducers radiate in two directions (0° and 180°) within a narrow angle of diffusion. At frequencies above 2 kHz they have an opening angle of about 4 degrees.
The lowest possible frequency of these loudspeakers is about 300Hz (The nominal frequency range is 300 - 22,000 Hz). The musically useful range is above approximately 600Hz. The spectral content below this frequency is thus assigned to conventional studio monitors. The crossover frequency at which the sound migrates to the electrostatic speakers can be adjusted individually anywhere above 300Hz. Although the electrostatic transducers only reproduce a fraction of the frequency spectrum, this fraction significantly affects the overall sound impression.
Due to the directionality and phase coherence of the resulting wave field the sound pressure remains stable in the direction of the main propagation for a very long time. The result is a web of „sound beams“ and „sound alleys“.
Because of the high degree of sonic focus and the low energy dissipation, the sound beams have a sharply defined area of aural impact. However, at the same time, the walls reflect very clearly audible sound back into the room.


Setup:
The system uses 12 electrostatic transducers. We envision that most of these are mounted on walls, to minimize the effect of reflected sounds. To emphasize the reflections from opposite walls as clearly as possible, the speakers are mounted significantly above head level. The closer one gets to the speakers, the stronger the perception of sounds from the surface of first reflection. As one moves away from the speakers, the direct sound clearly becomes dominant.
The exact setup will be made public after a testing phase in March. Details and progress updates can be found at the webpage of the Hochschule für Musik, Dresden.
During our testing phase in March we used the following setup:
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The system is designed to take up to 8 actual audio inputs. (eight-channel balanced jack, of those no more than 4 XLR microphone amplifiers, or 8 channels ADAT) or 8 channels of hard disc.
The signal range below circa 600Hz is covered by at least 6 Meyer Sound HD-1 loudspeakers. The special characteristics of this system, however, only come to the fore above 600Hz. For low-frequency music the system is quite unsuitable. Also, since the electrostatic units are not designed for high sound pressures, the system is better suited to softer sounds than massive volleys of sound.


Control: (described for single channel):
Each of the 8 separate inputs undergoes the following steps:
1. A branching filter (manually adjustable, usually close to 600Hz) splits the signal into a lower and an upper spectral component. The lower component goes directly to the Meyer Sound System.
The upper spectral range will be routed to a rotational movement within a virtual triangle. The points of this triangle usually correspond to the positions of three actual electrostatic loudspeakers.
The distribution of the three vertices among the physical loudspeakers is variable, however. Several points of a triangle can be routed to a single speaker, or the individual points of several different triangles.
This distribution can be changed in real time, or with the use of preset lists and tables.
In choosing movement types between the triangles, one must be cognizant of the particular qualities of the electrostatic transducers (narrow angle of diffusion, clearly audible reflections, etc.).
Rotation: within each virtual triangle the signal can rotate with variable speed and variable direction. Above a rotation speed of about 8Hz, the inevitable amplitude modulations lead to prominent sidebands, which begin to dominate the sonic image with increasing speed. The monitor speakers for the lower spectrum are not affected.
Since the intervallic distance between these sidebands correlates with the ratio between the rotation frequency and the lowest signal frequency, and since the rotation only affects the electrostatic speakers, the transition frequency between the ranges plays a significant role in the overall aural impression.
Previous experiments have demonstrated that, depending on the nature of the audio material, at a 600Hz transition frequency a rotation speed of 8Hz causes the sidebands to effect a much more pronounced change in the sound.
The rotation speed and direction within the individual triangles can be independently controlled and edited with a graphic user interface.
A maximum of 8 virtual triangles can be realized and mapped onto at least 12 electrostatic transducers via multiple allocations.


Further information:
Questions may be directed to the following email address:
E-Mail: FranzMartin.olbrisch@hfmdd.de