Performance Enhancing Subs

A ground-breaking multi channel reverb system forms a key part of an audio installation at the new Kunstlinie Theatre in Almere, Holland.

As DSP systems become more and more commonplace in modern performance venues, the uses to which they can be put above and beyond the usual mixing, EQ and distribution applications have increased. One such innovation is the so-called Multi Channel Reverb system or MCR. A recently completed example of this is the Almere province in The Netherlands’ new theatre “De Kunstlinie”.

MC What ?

Originally envisaged in the 60’s, an MCR system essentially involves acoustically enhancing a space by amplifying the reverberant sound. This gives the impression that the venue has a longer RT than is in fact the case.

Multiple channels make up an MCR system. Each consists of a microphone, an equalizer, a volume control, a power amplifier and one or more loudspeakers. Each channel is capable of increasing RT by approximately 1.25%, and the number of channels required can therefore be calculated from the original RT and the desired RT. Microphones are placed in the reverberant field to pick up the sound.

The Kunstlinie project was overseen and coordinated by Cees Wagenaar of Dutch theatre consultants Theateradvies BV, who wrote also the tender. The principle audio contractor was TM Audio under the eye of project Manager Reiner Bruijns, a part of the Ampco / Flashlight Group.

“I first became involved in the project back in 2002 with the consulting phase,” began Wagenaar. “We had a requirement for variable acoustics, to make the auditorium suitable for symphonic and other varieties of music. The original specification also called for the main system to be re-directable due to the movable proscenium arch bridge, beam steering was mentioned as a possible solution to this.”

TM Audio tendered two possible solutions, and Wagenaar’s main reason for selecting them to complete the project was that both solutions were workable, and well thought-out rather than being merely theoretical ones. They were also relatively low cost, making use of standard, passive products and accompanying amplification.

There are two key systems that make up the auditorium. The first is TM Audio’s solution to the requirement for variable acoustics. Part of this is actually already met by the ability of the auditorium’s ceiling to be “opened” with mechanical flaps. However this only achieves an increase from RT 1.1 to RT 1.5. Any further increase would need to come from electro-acoustic systems. The other system is the main house performance system.

The main system is based around Martin Audio W8LM line arrays. Eight units are employed each side – four upper and four lower, and these are powered by Martin Audio MA4.2 amplifiers. The upper clusters can be hoisted above the proscenium arch when they are not in use.

The system is supplemented by sub bass speakers mounted in the proscenium bridge. These are 12 Martin Audio S-15s and four XLNT Bassbeam loudspeakers (two per side) mounted halfway up the proscenium arch supports.

The lighting bridge which holds the upper line array speaker clusters moves up and down, depending on the show’s height. This means that the speakers need to be able to be adjusted in their facing, as Wagenaar explains: “The cluster is designed to cover every chair from every position. In the lowest position we need to reach the highest chair, but then the lowest cabinet is pointing towards the stage. So, we need to have control of each cabinet separately, we use different control – Team Projects wrote the software and we used the Nion frame with an output per cabinet; to keep the costs down we used passive cabinets with external Martin amplification”.

The MediaMatrix system responds to the height of the proscenium bridge by automatically adjusting the audio delay times for each cabinet. The beam alignment is also altered via DSP in one metre steps in real time. The operator needn’t do anything, the system merely recognises the height of the bridge and makes its own adjustments.

The MCR system comprises 38 small KEF C100 and C200 loudspeakers and 38 Shure microphones. MX391 and Easyflex boundary microphones are employed, in addition to MX202s in overhead positions. The 391s are mounted on balcony edges and concealed behind the metal grilles, and the Easyflex types are behind balcony front grilles. TM Audio selected the Shure equipment primarily for its very low noise floor, which was to be essential in a system designed to be completely aurally un-intrusive to the audience. The MCR system is driven by CM2208-8 power amplifiers from Crest Audio and does not require a great deal of power per channel.

The MCR (and the main house systems) is driven by a Peavey MediaMatrix Nion DSP, distribution and routing system. Three Nion 6s are used between the microphones and amplifiers processing the reverberant signal picked up the Shure equipment. These are controlled by bespoke software written by Team Projects, another Ampco / Flashlight group member.

18 MCR loudspeakers are arranged in a row, recessed into the ceiling each side of the balcony. The loudspeakers covering the main auditorium area – four per balcony level – are set behind the mesh covering the balcony fronts, and this renders them invisible to the audience. The intention throughout is that people are completely unaware that the room’s natural reverberation is anything other than that formed by the space itself.

However, this arrangement of speakers is not only useful for altering the acoustic properties of the auditorium. It’s a multipurpose venue and as such is not always used for symphonic performances. The system can also be switched for use as a surround sound system or for speech amplification. It can operate either of these functions whilst still also being used for MCR, perhaps to give improved acoustics for a conference or presentation.

Shared between both systems the DSP provided by MediaMatrix’s Nion processors is what makes everything possible. MCR relies entirely upon modern DSP. When it was first thought of, it would have required a separate amplifier, graphic equaliser and volume control for each channel. These would all have to have been manually adjusted. Using Nion, TM Audio and Team Projects have been able to supply the Kunstlinie an immensely powerful but flexible system.

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