In 2020, Müller-BBM Building Solutions was entrusted with the planning of the audiovisual systems for the construction of the new Volkstheater Rostock. In the year 2021, the client extended the contract by also commissioning the company, amongst other things, with the overall planning of the acoustics. The project manager Michael Prüfer introduced the planning.
The Great Performance Hall, the main venue of the new building, is a key focus of the acoustic planning. The target is to create optimal acoustic conditions for all the intended genres – drama, opera, ballet and concerts – without creating an excessive acoustic preference for one particular use over the others. The acoustic requirements of these disciplines, however, differ considerably. Drama requires excellent speech intelligibility, which calls for a room with comparatively short reverberation. Opera and ballet and, in particular, classical music, on the other hand, require significantly longer reverberation in order to achieve the desired liveliness, mix and spatial impression of the sound.
A compromise solution that places the reverberation between values that are favourable for music and speech is often unrewarding and ultimately fulfils neither use satisfactorily. For this reason, the concept of variable acoustics, which is common today and can adapt to the different requirements of the various areas, will be used in this case.
The largest absorption surfaces in the hall by far are undoubtedly the seating and the audience, which form the basic level of attenuation in the auditorium. The desired reverberation and sound impression can only be achieved if the ratio between the hall volume and the absorption from the seating and audience is correctly balanced. One of the first tasks in acoustic planning was therefore to determine an appropriately dimensioned auditorium volume, which should be large enough to enable the desired sound mix for music in the room, but at the same time not too large to ensure that a speaker on stage during a play can be easily understood by the last row of listeners, even without amplification.
In the selection of seating, acoustic aspects also play a major role in addition to design and ergonomics. In order for the seating to function optimally acoustically as the main absorption surface in the hall, certain sound absorption requirements must be met both when unoccupied and when occupied. To this end, sound absorption coefficient measurements will be carried out on sample set-ups of the planned chairs in an acoustic test rig. Such measurements enable acoustic adjustments and optimisations to be made to the chair structure before the actual production of the chairs begins.
The acoustic variability of the hall is determined by two elements: The first one is the hall volume. As regards a play, the volume of the auditorium determines the volume relevant for the reverberation. In operas, part of the stage must be acoustically coupled to the auditorium by means of a sounding board, which leads to an effective increase in the acoustic volume. And in classical concerts, an acoustically adapted orchestra shell achieves a further significant increase in the acoustically excited volume.
The second element of acoustic variability is the change of the attenuation in the auditorium space. For this purpose, large-scale variable absorbers in the form of textile sound-absorbing roller blinds have been planned, which can be extended from the auditorium ceiling and lowered in front of the auditorium walls. These absorbers are, as a rule, mainly used for theatre and electro-acoustic events.
A special feature of the project is the stage concept, in which the orchestra pit is part of the stage house. This poses particular challenges for the acoustic planning. The pit is not part of the auditorium, as is usual in many opera houses, which would fundamentally support a natural acoustic connection to the auditorium due to the architecture. As the orchestra pit zone and the area adjacent to it play a special acoustic role, the acoustician’s sphere of influence extends much more intensively to the stage house than in a concept with an orchestra pit in the auditorium.
Various measures have been planned to ensure optimum acoustic coupling between the pit and the auditorium. These include the creation of a sounding board above the pit that is optimised for reflection, lateral sound reflectors confining the proscenium along the side walls of the stage, a variable rear wall of the pit and an adjustable, sound-transparent pit parapet.
In addition to the perception of reverberation, acoustic impressions such as volume, distinctness, clarity, spatiality and support for the musicians are of decisive importance for the acoustic quality. These parameters are influenced by direct sound and the early reflections. Computer simulations are an excellent tool for analysing and optimising these parameters and will be used here in a variety of ways.
Jazz and pop concerts should also be possible under good acoustic conditions. The roller blinds for variable room attenuation will also be used for this purpose. A sound system optimally adapted to the acoustics and hall architecture will ensure outstanding sound. The sound reinforcement concept, which can be integrated into the architecture, is based on the basic principle of the linear sound source, a concept that has been used for a long time and achieves a high-performance concert level using state-of-the-art beam-steering technology.
Just as important as good room acoustics is the creation of ideally complete silence in the hall without background noise. To achieve this, all technical systems, in particular the hall ventilation, must be designed to optimise sound. The principle of displacement ventilation via a pressurised floor under the audience seats is best suited for this and will therefore be used here.
Special reinforced concrete ceiling constructions mounted on springs will be built to eliminate interference from internal sound transmission from the rehearsal stages on the floor below the auditorium and the restaurant on the roof above the stage house. To protect against low-frequency noise and vibration transmission from the tram that runs directly alongside the building, the tram route beneath the track bed has been provided with specially designed structure-borne sound insulation.
The second venue in the building, the space stage, will be equipped with a sound-insulating room-in-room construction for soundproofing reasons in order to allow unrestricted simultaneous use of the great concert hall and the space stage. The space stage will be equipped with room attenuation designed for good speech intelligibility.
In addition to these two venues, the numerous rehearsal stages, rehearsal rooms and the recording studio will also be designed with specific acoustics in mind. Particular emphasis will be placed on high sound insulation between the rooms as well as room acoustics that are optimised for the intended use.
A contribution from Michael Prüfer, Acoustic Consultant at Müller-BBM Building Solutions and as project manager responsible for the new Volkstheater Rostock.
A contribution by Michael Prüfer, Acoustic Consultant at Müller-BBM Building Solutions and project manager for the new Volkstheater Rostock.
This article appeared alongside the project article on the Volkstheater Rostock in the BTR Bühnentechnische Rundschau – Sonderheft 2024, p. 39/40.