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Variable acoustics, from design to everyday practice:
Can it really work?
Yann Jurkiewicz
To cite this version:
VARIABLE ACOUSTICS, FROM DESIGN TO EVERYDAY
PRACTICE. CAN IT REALLY WORK?
Y. Jurkiewicz
Kahle Acoustics, 188 avenue Molière, 1050 Bruxelles, Belgium
EXTENDED ABSTRACT
Many types of passive and active variable acoustics systems can be considered for a performing arts space, with various ways of influencing the acoustical characteristics of the room. But why exactly do we need to make the acoustics of a room adaptable in the first place? Is it always a sensible approach or should it be restricted to specific cases? And do these systems really work as intended in practice?
Opinions differ on these matters. Some continue to defend the usefulness of variable acoustics systems, while others stress the many cases where such systems are being considered useless and unpractical by the hall’s management and technical staff, and finally left abandoned. How can we understand these abandonments and can we avoid such waste of (public) money? Is the ideal of a single hall welcoming all cultures and types of events in the best possible acoustical conditions still plausible?
This presentation will not be intended to provide scientific answers to these questions. It will rather aim to open a debate by focusing on the most practical aspects of variable acoustics. The issues raised will be addressed through example cases of existing performance arts spaces.
The need for variable acoustics will be illustrated through two example cases. The Auditorium du Nouveau Siècle in Lille, France, was originally built in the 80’s as both a large congress hall and a symphony hall housing the rehearsals and concerts of the “Orchestre National de Lille”. Its design quickly turned out to be a bad compromise between the conflicting acoustical and technical needs of these two main uses. Its acoustics were unsatisfactory, neither for amplified sound nor for classical concerts. For its refurbishment in 2013, the strategy moved from “bad compromise” to “proper priority management”, with acoustic quality for symphony orchestra concerts placed at the top of the priority list. The addition of absorptive heavy velour curtains in the hall can temporarily tame down the acoustics for amplified events. But the need for variable acoustics can also be much more refined, as illustrated by the example case of Luzern KKL concert hall. Even in a concert hall purely dedicated to classical music concerts, optimal acoustic criterions vary depending on the size of
the orchestra and the repertoire played. Adjustments of reverberation time are not sufficient to allow for excellent acoustics for both large romantic orchestras and small ensembles of baroque music. In Luzern KKL, a complex variable acoustic system was designed for that purpose, allowing an independent tuning of the amounts early-reflected acoustic energy and late reverberation.
Figure 1. Rotating walls and reverberation chambers in
Luzern KKL concert hall.
Variable acoustic devices generally cost a significant amount of money, and not all performing arts spaces can afford to be equipped with a system as complex as in Luzern KKL. But this is often not the main reason given by customers to rule out the installation of acoustic variability in a room. The many example cases of misused or abandoned variable acoustic devices in existing halls are a stronger argument. Badly designed and anecdotic variable acoustic devices are rarely used as initially intended by the design acoustician. Examples
include, but are not limited to, overly loud and resonating orchestra shells, as well as variable absorptive finishes provided in an too small amount to generate a sufficiently audible change. Overly complicated and unintuitive variable acoustic systems are difficult to handle by the technical staff and finally also rarely used properly. When variable acoustic systems also have non-acoustic roles (blackout or light filtering curtains, movable walls, etc.), the risk of misuse is further increased. But in some instances, it can also be observed that even simple, intuitive and efficient variable acoustic devices can be used wrongly. The responsibility of the technical management of the hall then arises.
With so many examples of wasted variable acoustic systems in existing performing arts spaces, a tendency to avoid or forbid them for new constructions and refurbishments can be observed. When the context of a project is not favorable, it is indeed sometimes wiser to avoid variable acoustics. The official mission of French “Scènes Nationales” is to accommodate all type of shows from Drama Theater to pop-rock concerts, and from one-man shows to symphony orchestras. Most of them were designed with fixed acoustics, generally at the expense of classical music and traditional non-amplified drama theater. The Paris Philharmonie shares with the “Scènes Nationales” this French paradigm of one single hall housing all cultures and welcoming all types and sociological profiles of audience. But this time no compromise was made on acoustic quality. Complex and expensive means of acoustics and architecture variability make it possible to for rock fans and classical music lovers to attend concerts in the same hall in equally good acoustic conditions. That solution would however be difficult to replicate throughout the country. An alternative solution for limiting the needs for variable acoustics with no compromise on acoustic quality is to build cultural complex including several halls, each of them being designed for a specific type of events. The example of Stavanger Konserthus, Norway, illustrates that even such cultural complexes still have a need for variable acoustic devices in each of the halls.
In practice, existing halls provide only very rare examples of halls with always-satisfactory acoustic quality without the help of a variable acoustic device. If we cannot get rid of variable acoustic systems, what can we do to prevent their misuse? Some successful cases such as Stavanger Concert Hall, and observations of less successful ones such as Dijon Auditorium, can shed some light on possible solutions. Acoustic consultants are responsible for the long-term monitoring of the rooms they have, and for educating and coaching the technical management staff.
Figure 2. The four main acoustic configurations of
Fartein Valen Hall, in Stavanger Konserthus. From top to bottom: symphony orchestra setting, chamber music setting, brass band and loud ensembles setting, heavily amplified music setting. Variable acoustics elements are colored as follows: movable ceiling in green, movable canopy reflectors in blue, motorized absorptive curtains on tracks along the side walls in red, vertically deployable absorptive curtains coming out of the movable ceiling in purple and yellow.
