The perfect illusion in image and sound

28.12.2021

The corona related distancing regulations for choristers required an unusual solution to make the Bayreuth Festspielhaus performances possible. One half of the choir acted scenically on stage while the vocals of the remaining, remotely singing choir was recorded. Müller-BBM Acoustic Solutions GmbH, among others, was responsible for the elaborate realisation of the electro-acoustic transmission.

Festivals under corona conditions are an extreme challenge for all involved. After the numerous cancellations at short notice in the 2020 festival season, this year there was more time for preparation and at least a slightly more reliable knowledge of the requirements and legal framework for major cultural events. In addition, the previously unimaginable cancellation of the last Bayreuth Festival season strengthened the will of all those involved to make the impossible possible.

For the Bayreuth Festival, this meant, in addition to a variety of additional challenges such as setting up an extensive test infrastructure, finding a solution for the Festival Choir. The legal distancing regulations for the choir with a distance of 6 meters to the front and 3 meters to the side to the next chorister were consistently impossible to implement in all Bayreuth productions. The only alternative, therefore, was to move the choir out of the hall and transfer it electro-acoustically to the stage of the Festspielhaus. This was to be realised by splitting the choir into one half, which sings in the choir hall, while the other half acts silently on stage. The choir in the choir hall then had to be recorded with microphones and transmitted live to the Festspielhaus via loudspeakers. The goal set by festival director Katharina Wagner was to achieve the highest possible naturalness in the sound image, so that the illusion of a singing choir can be created on stage and the overall experience for the audience remains harmonic and distraction-free.

3D audio solution and many questions – from miking to monitoring

It was obvious that this goal could not be achieved with conventional stereo sound. The task could only be solved by using modern 3D audio sound methods. But what would the appropriate loudspeaker layout look like if the desired naturalness had to be ensured, but each additional loudspeaker represented a real burden in the complex operating procedures of the festival? The necessary miking in the choir hall, the monitoring for the choristers, and the details of the required sound design were also open questions that had to be clarified in a series of tests and test setups.

The first major test took place in mid-December 2020 at the Festspielhaus. Here, the portal frame area was equipped with five small d&b T10 line arrays suspended from a stage hoist and six stage edge loudspeakers. Fohhn Focus Modular line array loudspeakers were suspended on both sides of the stage opening. These had been planned earlier for permanent installation for speech reinforcement and effects, so that the setup could simultaneously serve as a quality and optimisation test for these sound reinforcement tasks. On the empty stage, d&b E8 loudspeakers were set up on tripods in positions that would accommodate three exemplarily selected stage sets.

Recordings of the stage edge microphones from the 2019 Festival were available for playback in this test. These were distributed as sound objects on the stage and distributed to the loudspeakers with the help of a Vivace 3D Audio Processor with the appropriate levels and delays.

At the same time, specially designed booths were set up in the choir hall for four choir members as a test setup. In order to minimise the risk of mutual infection among the choir members at the small distances possible and necessary for singing together, aerosol protection had to be created to the rear and to the side for each individual singer. The booths built for this purpose by the Festival consisted of a wooden substructure covered with a transparent and largely sound-transparent film in the upper area and an absorbent molleton fabric in the lower area. In this way, the view of the conductor as well as mutual hearing was still possible, at least to some extent. The arena-shaped arrangement and gradation of the choir seats in the choir hall was very advantageous.

Testing, planning and finalising

In addition to confirming the basic feasibility, this first test provided numerous insights for the further planning and implementation of the choir broadcast. On this basis, public tenders for the components to be rented and permanently installed could be initiated, so that at the end of March 2021 a further test setup could be carried out in the Festspielhaus with the equipment that was then already largely finalised.

During this test, the line array loudspeakers had already been permanently installed on the side of the portal frame and covered in accordance with the preservation order. Openings for the line arrays had been cut into the mobile portal bridge, so that these loudspeakers could also already be mounted in their final positions. The loudspeakers in the stage sets were again implemented by means of free-standing tripods on the empty stage. All 70 individual booths had already been set up in the choir rehearsal hall. A coarse-meshed steel net suspended above the booths created the possibility for exact positioning and interference-free wiring of the microphones. A newly laid fibre-optic connection was used to transmit the microphone signals to the Festspielhaus and, in the opposite direction, to send the piano microphones in the orchestra pit to the choir hall. For control and signal distribution, a rented Yamaha PM7 mixing console was available in the auditorium with breakout boxes in the choir hall and by the amplifiers on stage.

The choir of the Chemnitz Opera could be engaged for the date at short notice, so that testing could already be carried out under largely real conditions. In addition to great progress in the sound quality achieved, the second test run in the Festspielhaus yielded some important optimisation steps. Thus, the microphone system was expanded to 38 individual microphones, which could then be positioned and moved around the stage as 38 sound objects. For the choir, monitoring via wireless headphones proved to be a viable option, completely avoiding the need to speak a monitor sound into the microphones.

For the loudspeaker layout, the test provided evidence that the loudspeakers to be installed in the stage sets have an important influence on the plasticity and depth effect of sound and are therefore of great importance for the desired naturalness. The distribution of the sound energy of the choir to the loudspeakers in the stage set and to the loudspeakers around the portal could very well ensure that no unpleasantly high sound levels were generated by the choir recording, neither for the soloists and the playing choir on stage nor for the musicians in the orchestra pit.

Furthermore, it became clear that naturalness also includes the reaction of the room to the choral voices reproduced via loudspeakers. In direct comparison with the choir distributed corona-compliant over the stage area, it became clear that the famous spatial sound of stage and the Festspielhaus cannot be adequately stimulated with the loudspeakers available per set. Therefore, eight additional loudspeakers were installed in the auditorium until the start of the rehearsal phase in May 2021. With the aid of electronic room acoustics, it was thus possible to achieve the appropriate embedding of the choral signals in the room sound as well as the natural distribution of the choral sound in the higher dynamic levels.

Adjustments and connections for loudspeakers in the stage set

For the workshops and the sound department of the Festival, a very grueling time began following this test. Suitable loudspeaker positions had to be implemented for the stage sets of all choral scenes from the productions Meistersinger, Tannhäuser and Holländer scheduled for 2021. In coordination with the stage designers of the productions, cutouts were made in the largely existing stage sets and closed again in a sound transparent manner so that as little difference as possible could be perceived. An actually unsolvable task, which the scene painters of the festival mastered brilliantly. Loudspeakers were used at positions on empty stage areas or in the area of a mobile revolving stage. These loudspeakers were equipped with radio receivers and rechargeable batteries and were partly brought into position by the choir performers. For these loudspeakers, additional coverings had to be designed to match the stage set.

During this time, the sound department had to create and implement an elaborate concept of how to connect all the loudspeakers and how everything could function smoothly, especially during open transformations. In total, 42 permanently mounted loudspeakers and 18 loudspeakers with battery operation were in use in the stage sets. A special challenge for the control in the 3D audio processor were the loudspeakers housed in the remote-controlled mobile houses during the Holländer production. Fortunately, the finalisation of the control concept meant that the houses did not have to be moved during the choral scenes.

Finetuning and magical moments

Before the start of the stage rehearsals with choral participation, a full day was shovelled free in the tightly timed schedule of the house for each production, on which the relevant stage sets were built one after the other and then the technical calibration of the entire system was carried out. In the course of the piano and orchestra rehearsals that followed, the positions and movements of the choir on stage were programmed and the tonal settings optimised. Especially for the fine-tuning of the choir sound with the choir director and the artistic direction, there were also two extra added choir rehearsals.

During the rehearsals, the Festival’s sound engineers controlled both the positions of the choristers on stage and the feed levels or filtering of the individual microphones from the hall mixing console. With the start of the dress rehearsals, the entire operation was relocated to a loge in the 1st tier, which made the correct level control even more challenging. In parallel, the sound department had to supervise miking and monitoring in the choir hall as well as ensure smooth communication between the conductor in the hall, the choir conductor, the stage and the director.

The magnificently successful, tight interlocking of the sound engineering tasks and requirements with so many technical trades of the house and the entire artistic staff is one of the great special features of this festival season. A multi-layered and transparent choral sound for all audience seats in the Festspielhaus with natural localisation and sound dynamics were the reward for the enormous and energy-sapping effort of all involved.

In the concert performance of Parsifal with Christian Thielemann toward the end of the season, truly magical moments could thus develop. A result that was only possible with the unconditional will of all to exploit the technical possibilities and put them in the service of music.

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