Maintaining the gold standard

“Make sure the acoustics don’t suffer,” was a key remit for the planners of the conversion and extension work on the main hall of Leipzig’s Gewandhaus. More than that, it proved a good opportunity to improve the acoustics on the platform itself, as requested by the orchestra musicians. On successful completion of the refurbishment, the hall was officially re-opened at the start of the 240 th  season at the Gewandhaus in autumn 2020. 

Bühnentechnische Rundschau

The motto of the Leipzig Gewandhaus and its orchestra,     res severa verum gaudium     – ‘true pleasure is a serious business’, reflects the complexity of making and performing music with excellence. And this motto rang true for us acousticians, too, as we participated in the extension and conversion work on the time-proven, 40-year-old concert platform and surrounding walls. The main hall of the Leipzig Gewandhaus is renowned not only for its outstanding acoustics.

Its architecture is up to date without having any of the affectations of modern acoustics designs. The Gewandhaus orchestra is one of the leading orchestras in the world and plays under preeminent conductors. 
We needed to bear all this in mind when planning the refurbishment of the platform, which started in 2017. The time was considered ripe because of the advanced age of the stage machinery and the increasing frequency of third-party events in the hall, requiring many quick reconfigurations. The old raising platform had limited flexibility and durability. A new one with extended functions was to be fitted in an adapted layout. 
Where the acoustics were concerned, the main goal was to ensure the quality of sound in the hall while planning and designing the new platform and advising on the new floor construction. Ultimately, the concert hall directors gave us acousticians free rein, which allowed us to make some excellent, effective adjustments.
An initial stock-taking quickly showed that the prevalent view of the concert hall as the ‘acoustic gold standard’ is absolutely justified. The hall offers top listening experiences. Unlike in some modern halls, nothing about the existing form needed improving; the sound is even and transparent without any loss of sonority. In terms of acoustics, the main hall can compete with any of the other major contemporary concert halls and even outshine many of them.

Acoustic quality on the platform
While the platform made a dazzling impression, so to speak, from the auditorium, the musicians themselves had a few problems with it, and had done for several years. After attending several rehearsals and concerts and talking to the orchestra musicians, we realized that playing conditions were not great on every part of the platform. Contact between the musicians at the front and back of the platform, especially, was less than ideal.  
A more precise analysis of the platform confirmed the musicians’ reports. Some sections had too little performance contact with other sections. Being seasoned professionals, the musicians were able to smooth over these difficulties, but the situation remained dissatisfactory. What was the reason? The relatively open construction of the Gewandhaus platform did not leave enough sound on the stage for the musicians to hear each other. In many concert halls, this is ​compensated for by sound sails, that is, suspended canopies, especially when the ceiling is extremely high. In the Gewandhaus, the ceiling is only about 15m above the platform. Plus, there is the surround concept to consider. You need undisturbed reverberation room over the platform to achieve good sound in the auditorium. Here, ceiling sails would have a negative effect on sound dispersion. 
To nevertheless improve the acoustics on the podium, we worked out a plan of measures, concentrating on the walls and parapets enclosing the platform. The main objective was to improve sound coverage on the platform without sacrificing any in the auditorium. The plan comprised the following six points:

Consult musicians and change the orchestral seating arrangement
The ensemble sound in the hall and the sound on stage are tremendously important for the musicians. For this reason, after the first phase of construction and before we did any work on the acoustics, we started off by asking their views. Getting an impression of the musicians’ feelings was extremely important for working out their needs and wants, both from the point of view of individual sections and of the orchestra as a whole. It turned out there was a strong school of thought for getting the orchestra to sit further back on the platform in future. Experience has shown that this can improve contact within the orchestra because it allows the string sections at the front to sit closer to the reflecting walls. And crucial reflections are lost if the front string sections play too close to the edge of the platform. 

Narrow the enclosure 
The side walls previously opened on to the auditorium at an angle of about 16°. This relatively wide opening resulted in too little sound on the stage. An acoustic inspection showed that changing the angle would likely lead to a distinct improvement in the ensemble effect. As the platform was due to be widened along the back wall, the solution was to pull down a structurally unimportant nogging wall. This created enough space to go “deep down” and twist out the wall. The front of the platform was turned in toward the stage. The platform now opens at an angle of between 8° and 12°. 

Apply a diffuse structure to the side walls
To achieve a sufficient change in the angle along a length of some 10m to 11m, the previously smooth side wall was restructured with jagged ‘sawtooth’ elements. Rumpling the walls also provided a sound-scattering surface, further helping to disperse sound. 

Tilt a transitional panel forward
On a platform that opens out into the auditorium, the high strings, especially, often sit a little too far apart. Additional lateral reflections could be generated by pointing the reverting transitional panel B3, (symmetrical on left and right) toward the platform rather than the ceiling.

Perforated risers in the horn section
The musicians explicitly asked for an adjustment to the acoustics in the horn section. This improvement was achieved by means of perforated risers, or screen sections, though only a very small part of the sound is lost in the perforated surfaces. 

Semi-absorptive panels on the back wall
We found the large, smooth surface of the back wall to be responsible for a lot of harsh sound reflections behind the percussion group and the heavy brass. To increase acoustic transparency, we decided to attach a semi-absorptive surface. 

Implement the ideas and put them into operation
The renovated platforms were put into operation at the start of the 2019 and 2020 seasons. Thanks to our close and in-depth communication with the orchestra, technical directors, artistic directors, and all those involved in the planning, we achieved a fantastic result. For one, the platform acoustics were noticeably improved; all the goals of increased acoustic quality and transparency on the platform were appreciated by the musicians. 

And the audience? They benefit from improvements in the hall acoustics, too. Through the work on the platform, we achieved a warmer bass sound and a more precise alignment of the brass players. The response from music lovers and the press was entirely positive. The Gewandhaus is now technologically and acoustically all set to celebrate its 40th anniversary and provide more ‘true pleasure’ in perfect style. Even more reason for the orchestra and the public to look forward to the Gewandhaus’ reopening after the Corona-enforced break.

BTR Ausgabe 2 2021
Rubrik: English texts, Seite 116
von Winfried Lachenmayr and Karlheinz Müller

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