Amadeus, Solid State Logic (SSL), Lab.gruppen and Sonic Emotion recently joined together to design a one-of-a-kind electro-acoustic ‘3D sound’ reinforcement system for Paris’ Chaillot National Theater.

The sound reinforcement system used in the 1,270 seat Jean Vilar hall was due to be replaced, leading Amadeus to imagine a solution that would go beyond the limits of traditional technologies such as stereo, 5.1 multichannel format, or any conventional speaker system. The implemented solution uses the Wave Field Synthesis (WFS) technology. Like visual holograms, this ‘holophonic’ process captures or creates a sound stage by preserving spatial information: the distance and direction of the sound sources used.

“This technique allows us to replicate the sound field’s physical properties,” explains Marc Piera, Chaillot National Theater’s sound department manager. “Wherever they are in the theatre, the listener keeps a coherent perception of the sources’ localisation.

“I personally consider that the systems using a single-dimension speaker network, like line arrays, are inept for sound reinforcement in most theatre buildings,” he discloses. “These systems were primarily designed for open field concerts where the audience area is very wide and very deep, and most of the time, on a flat or lightly sloped ground. They create a uniform sound pressure field, but most often they degrade the sound image for most of the audience. The Jean Vilas hall’s intrinsic technical, acoustical, physical and mechanical properties led us to prefer an original sound reinforcement system, based on a ‘holophonic’ concept. Listening conditions are thus identical for all spectators, wherever they are in the hall.”

Photo: Atlantide Phototravel

The Jean Vilar hall’s bleachers are segmented in four sub-spaces, each of different dimensions, seat numbers and slopes. The bleacher’s curvature is almost exponential, with 16°-, 23°-, 25°- and 35°-slopes. The control room sits 12 meters above the ground. The spectator area has a surface of 1122sq-m (33m-deep, 34m-width).

“A traditional line source system, with constant or variable curvature, placed in a classical configuration, would inevitably have affected the sources’ localisation, according to Haas’ effect,” Marc elaborates.

“In the 1940s, this German scientist established that a source’s localisation is given by the direction of the first sound reaching the ear (direct sound). If the difference between the spectator’s position, the primary source and the secondary source grows, the this effect becomes stronger.”

“I personally consider that the systems using a single-dimension speaker network, like line arrays, are inept for sound reinforcement in most theatre buildings” – Marc Piera, Chaillot National Theater’s sound department manager

Chaillot National Theater technical manager, Denis Desanglois intended to replace the sound reinforcement system, which he says “had not been completely satisfying until now. We wished to abandon the stereophonic paradigm, the line array-type. So we implemented a WFS-based system prototype and asked the companies we were working with for their feedback. Some technicians were totally initially disoriented, but eventually everyone was happy, technicians and artists alike. The sensations of listening are completely different, wherever you are in the hall, you experience the same sound, that’s pretty amazing. We even integrated a 24-speaker ramp in the front end of the stage, to avoid the usual ‘sound hole’ first row of seats!”

Photo courtesy of Amadeus

What Is Wave Field Synthesis?

Based on Huygens’ Principle (1678), the idea of Wave Field Synthesis (WFS) was developed in the Netherlands in the 1980s by the Delft University of Technology. WFS concept makes it possible to synthesise ‘sound holograms’ by simulating acoustic waves produced by virtual sound sources. To do this, the system uses a large number of loudspeakers, regularly spaced and used conjointly. They are each controlled with a delay and a gain to form a wave that emanates from the desired location of the virtual source. This process is repeated for each sound source in the sound scene. The major benefit of the WFS technique is to create a coherent sound field in an extensive area, therefore preserving the fidelity of the spatial image – the position of the sources – even for listeners located at the periphery of the zone or for listeners moving within the zone.

“The basic concept of this approach is to use an array of loudspeakers for the physical creation of virtual source sound fields,” Marc tells CIE. “For this each speaker of the array is driven with an individual signal, so that a correct sound field of a virtual source is generated by superposition of the sound waves radiated from the speakers.

“Since the Renaissance, people placed close to the stage are, paradoxically, the less privileged spectators. Limelight, candlesticks or oil lamps, generated a dense fog, intruding between spectators and the stage. A few centuries later, this fog left, only to place a ‘sound hole’ there for the same spectators.”

“In contrast to the channel-based audio reproduction this approach is called object-based. While the channel-based approach only requires the playback of ready-mixed loudspeaker signals, for the object-based approach the loudspeaker signals have to be calculated in real-time using a mathematical model of the sound source object.”

“The major benefit of the WFS technique is to create a coherent sound field in a vast zone, therefore preserving the fidelity of the spatial image (i.e. the position of the sources), even for listeners located at the periphery of the zone or for listeners moving within the zone,” he explains.

Photo courtesy of Amadeus

“Another interesting property of the WFS is to enable, at least partially, the synthesis of the reproduction of the sound sources, simulating the effects of directivity and orientation of a voice or of a musical instrument. By approaching the natural reproduction of the sources and their interaction with the room, this technique reinforces the impression of the presence of the sound sources in the room.”

Michel Deluc, Amadeus’ R&D manager, elaborates further: “Edgard Varèse, one of the twentieth century’s pioneering composers in terms of sound spatialisation, said a century ago: ‘tomorrow’s music will be spatial’. At Amadeus, we have believed in this statement since the company’s beginnings, in 1992. We worked with the Institut de Recherche et Coordination Acoustique/Musique (IRCAM), to develop the multichannel sound spatialisation equipment used in their Espace de Projection (ESPRO). This led us to develop the install’s 339 custom-made loudspeakers. Transposing this technology for the Chaillot National Theater, thus allowing large audiences to experience it, is a thrilling and edifying challenge.”

Photo courtesy of Amadeus

Speaker Placement: Filling The ‘Sound Hole’

A first line of passive coaxial loudspeakers has been integrated in the front edge of the stage (in a 12cm-deep, 18cm-high volume). These 24 loudspeakers, variants of Amadeus PMX 4 model, form a large-scale ‘sound bar’; they are evenly distributed across 18m, with 75cm between each adjacent speaker. This first line seamlessly covers the first row of seats.

“Since the Renaissance, people placed close to the stage are, paradoxically, the less privileged spectators,” Marc points out. “Limelight, candlesticks or oil lamps, generated a dense fog, intruding between spectators and the stage. A few centuries later, this fog left, only to place a ‘sound hole’ there for the same spectators. Electro-acoustical sound reinforcement aimed for these first-row spectators is often too inefficient, if not missing. Staging allowing, a small ‘front fill’ speaker is tolerated at best. Here, Amadeus’ sound ramp is seamlessly integrated to the location’s scenography, and it’s perfectly dimensioned for our purposes; it redefines the perception of sound and, at last, offers these spectators a real sound and sensory privilege.”

“This setup redefines the perception of sound and at last offers the audience a real individual sensory experience of the sound. This is the first time that such a system has been installed in a national theatre in France”

The second line of loudspeakers is comprised of 11 Amadeus UDX 15 active coaxial speakers with remote bi-amplification. These loudspeakers are evenly spaced across 23.5m and they are placed at 9m height. This line covers the first two thirds of the bleachers. A third line is made of 11 Amadeus UDX 12 active coaxial speakers with remote bi-amplification. These loudspeakers are evenly spaced across 23.5m and they are placed at 9m height. This line covers the first two thirds of the bleachers.

A fourth ‘surround’ line is made of six Amadeus UDX 12 active coaxial speakers, with remote bi-amplification, hung to the second technical bridge. A unique bass reinforcement system is set up on lateral first level technical bridges, on left and right-hand sides, comprised of six Amadeus MAESTRO subwoofers, each hosting two long-excursion speakers, loaded by a folded hyperbolic horn. Rear acoustic wave rejection is optimised via a specific baffle.

Photo courtesy of Amadeus

This sound system is completed with an SSL Live L300 digital mixing console, used with two Network I/O SB 8.8 (eight analogue I/O each) and two Network I/O SB i16 (16 analogue inputs each) Dante stageboxes. The SuperAnalogue technology used in these SSL-developed interfaces ensures clarity and precision.

“Audio over IP allows us to put the stageboxes where needed, with minimal and redundant cabling, and to connect on the network all kinds of Dante-enabled gear: Amadeus sound reinforcement system, SSL L300 console, SSL Network I/O stageboxes, and every other ancillary equipment needed,” says Philippe Guerinet, director of international sales for SSL and SSL France manager.

“This network approach notably allows us to solve classic problems, like signal distribution without adding any TDM routers; there’s no loss, either noise induced in the audio signals, and latency is particularly low. Last but not least, the technical solutions chosen by the Chaillot National Theater ensure total flexibility and an astonishing audio quality, for a surprisingly affordable budget.”

“This setup redefines the perception of sound and at last offers the audience a real individual sensory experience of the sound,” Marc enthuses. “This is the first time that such a system has been installed in a national theatre in France. By hearing the feedback from mixing engineers, directors, musicians and spectators, I truly believe such distinguishing technologies will be installed in other venues.”

Photo by Bill Ross

Kit List

Amadeus

  • Custom-made sound ramp, made with 24 PMX4-type loudspeakers, 4-ohm version (4’’ LF + 0,4’’ HF): 1 unit
  • 2-way Active Loudspeaker Amadeus PMX 15 (15’’ LF + 2’’ HF) : 4 units
  • 2-way Active Loudspeaker Amadeus UDX 15 (15’’ LF + 2’’ HF): 11 units
  • 2-way Active Loudspeaker Amadeus UDX 12 (12’’ LF + 2’’ HF) : 17 units
  • Push-pull subwoofer, with ultra-high efficiency, hyperbolic folded horn and custom-made baffle (2 x 12’’ LF): 6 units

Solid State Logic

  • Network I/O SB 8.8 Dante stagebox (8 Mic/Line analogue I/O): 2 units
  • Network I/O SB i16 Dante stagebox (16 Mic/Line analogue inputs) : 2 units
  • Console SSL Live L300: 1 unit

Sonic Emotion 

  • WAVE II 3D sound processor (64/64 MADI I/O)

Lab.gruppen

  • C10:8X power amplifier (8 x 125 W/8 Ω, analogue I/O): 3 units
  • IPD 2400 digital power amplifier , with DSP (2 x 600 W/8 Ω, analogue & AES3 I/O): 32 units
  • C88:4 power amplifier (4 x 1250 W/8 Ω, 4 x 2100 W/4 Ω, 4 x 2200W/2 Ω, analogue I/O): 2 units
  • Lab.gruppen NLB 60E NomadLink remote control: 1 unit