Karlheinz Müller: Master of acoustics

With a contented smile, Karlheinz Müller described himself as «proud and relieved». His work at the Tonhalle in Zurich began twenty years ago - and was finally completed with the renovated concert hall reopening at the beginning of September. «And the first musicians to play here confirm our own results - the acoustics are even better than before.»

That was not a given, because even before the renovation, the Tonhalle, built in 1895, was acclaimed by orchestras and the public alike as an outstanding venue for classical concerts. And that was despite the fact that when it was built there were no acoustic engineers like Karlheinz Müller around. How could that be? Müller laughed. «Because the composers of the time composed their works to resonate very dramatically in these halls - they were all amateur acoustic engineers.» Acoustics did not become a serious topic until the arrival of radio broadcasting in the 1920s and 1930s.

According to Müller it is much more challenging to enhance the acoustics when renovating a prestigious concert hall than it would be in a new building. «There are many aspects that we have to work with - and making something that is already good even better isn‘t easy.» But the acoustics engineer, who hails from Munich, and who no-one would believe is eighty years old, brings decades of experience with him, having upgraded the sound quality in concert halls all over the world, including the New York State Opera and the Teatro del Lago in Chile. Müller-BBM, the firm he works for, was established by his older brother, and belongs to the world‘s premier league of acoustics experts. «But nowadays I work with much younger colleagues and no longer take on projects, but act more in an overall guiding capacity.»

measuring instruments, we moved square meter by square meter throughout the entire hall, along all the walls, right up to the ceiling. During rehearsals, but also when the concert hall contained a full audience.» They also talked to the musicians themselves - all with the aim of discovering what is already good and why. And where at one time the hall might well have been better, where the weak spots are. «It was these that we tried to improve during the restoration work.»

He is clearly very happy that he achieved success with the prestigious Tonhalle. «The main objective was to have a good bass section and to amplify the sound of the higher tones so that they resonate longer,» he explained. «And it‘s not just two or three things that need to be adapted, there are countless tiny setting screws that you have to turn just a little bit - a laborious and fiddly task, which is often undervalued.» Müller also had an influence on the choice of flooring, the new podium, the reinforced ceiling, the sealed windows and even the colours. «We truly checked out every single component that was being restored for its acoustic character.»

Occasionally, what an acoustic engineer wants conflicts with the client‘s own ideas and financial resources. «We cause expense, but can rarely say exactly how much the acoustics will be improved by spending the money,» said Müller. «So it helps to be capable of a certain amount of diplomacy.» However, with his work on the Tonhalle, he was able to do everything he wanted. «But in the past, we have refused contracts, when it became clear that the differences between us and the client were too great.»

Works to renovate and restore the Tonhalle and Kongresshaus began in 2017. The concert hall was restored to close to its original 1895 condition, but with the most up-to-date technology. During the works, the Tonhalle orchestra played at a temporary venue on the Maag Areal, where everyone was surprised at the start by the good sound. Müller was responsible for that too.

But what actually does it mean to have good acoustics? «We can argue a great deal about that,» said Müller. «But in principle the orchestra wants the room to hold the music it performs and convey it to the audience in the best way possible. In turn, the audience wants to be enveloped in the sound, and feel the resonance.» Ideally, the sound should be neither too clear nor too indistinct. «Those who prefer a clearer sound should sit towards the front of the hall, while those preferring a sound cloud should sit towards the back.» However, the Tonhalle does not have such major differences. «The hall provides a very uniform sound.»

For concert-goer Müller, poor acoustics cause his thoughts to stray to the point that the music no longer captivates. «A clear sign that either the orchestra is performing badly, or the acoustics are.» He concedes that a good performance is ultimately more important. «Even good acoustics will not rescue a poor performance. But acoustics will enhance - almost enoble - a good performance.»

The basic architecture and the materials are crucial here. «A round building is difficult for a classical concert hall, rectangular or multi-angled shapes are better.» A concert hall made entirely of glass would also be unsuitable. «But there is no material that cannot be used - it‘s just a question of how much, the way they blend together, and where they are placed.»

Concert halls like the Tonhalle are not, however, suitable for electronically amplified sound. «Heavy metal would not be a pleasure here,» explained Müller, «it would simply be muffled sound because the hall is acoustically so alive.»  Heavy metal? Oh yes, the sensitive 80-year-old likes other genres besides classical sounds. «But I always wear earplugs if I go to a rock or metal concert.» And even if he finds that kind of music exciting, deep in his heart he is more moved by classical music from the baroque period through to the late romantic and modern classics - or jazz.

Karlheinz Müller grew up in a very musical family and while at school played in a Dixie band. He «sort of fell» into acoustics when his brother founded the company. Originally he was a construction engineer, so he brought with him an ideal combination of technical affinity and an interest in the arts. «A good acoustics engineer needs both because figures and calculations are an important part of the work which covers physics, music, and construction engineering.»

Müller-BBM doesn‘t only take on concert hall projects. Acoustic engineers are also in demand where noise needs to be reduced, for example on railways, motorways, and in vehicle engines. However, Müller specialises in concert halls - and loves attending concerts of every type, preferably in a concert hall with good acoustics. For professional reasons he occasionally visits halls with less than ideal acoustics. «Ultimately you need to know what it sounds like, what you are trying to avoid.»

For further information: tonhalle.ch, seeyouamsee.ch

The opening concerts take place on 15 and 16 September. The Kongresshaus and the Tonhalle can be visited on 4 and 5 September.

Photo/stage: Désirée Good