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Acoustic design: Preserving Powell Hall’s Signature Sound

By Eric Dundon


Close your eyes and imagine the sound of Powell Hall, the St. Louis Symphony Orchestra’s home. What do you hear?


Maybe it’s a warm sound that envelopes you from all sides. Or perhaps it’s the great clarity that transports even the most nuanced phrase to the back of the room.


For Stéphane Denève, The Joseph and Emily Rauh Pulitzer Music Director, it’s a beautifully melting sound.


“The warmth and cohesion of sound in Powell Hall are remarkable and impressed me from the first time I conducted the orchestra in 2003,” he said. “It is a bass-friendly hall, with indeed a slight prominence of the lower register, which builds a rich, deep, and powerful harmony and yet gives a feeling of comfort.” 


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A rendering of the renovated auditorium shows the new shape of the rear wall of the floor and new curved walls near the stage that will change the sound reflection on the pattern on the floor.

That cohesion of sound has earned Powell Hall a national reputation as one of the finest concert halls, notable for its warmth and resonance.


Enter Kirkegaard, a design and consulting firm with an office in St. Louis that specializes in architectural acoustics and has worked on renovations of Carnegie Hall and Chicago’s Orchestra Hall. The firm is a core partner in the continuing expansion and renovation of Powell Hall.


“A top priority for the expansion and renovation of the venue is to protect this acoustical jewel. Kirkegaard brings a wealth of experience that makes the firm a perfect match for this complex project,” said Marie-Hélène Bernard, SLSO President and CEO.


Acoustic Modeling

Long before the first shovel overturned dirt on the project, Kirkegaard extensively studied and tested the acoustical qualities of Powell Hall, understanding its strengths and potential areas for improvement.


“It was critical that we understood the acoustics of the hall before making any recommendations,” said Brian Corry, St. Louis-based Partner at Kirkegaard. “Our multiple days of testing in the hall allowed us to develop and calibrate a model that was later used to influence some of our design choices.”


Part of Kirkegaard’s studies included 3D mapping of sound movement in the auditorium, using “blasts” like popping balloons to chart the path of soundwaves throughout the space. Imagine a series of billiard balls hit with force. From the cue stick, the balls react to the edges of the table, bouncing again and again until they come to rest. Similarly, Kirkegaard’s modeling created a 3D animated graphic of how sound reacts to the surfaces in Powell Hall.


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This diagram, part of Kirkegaard's acoustic modeling, shows how new walls near the stage will reflect sound to the center of the main floor.

The results, which look like a laser light obstacle course from a spy movie, revealed a strong degree of acoustic support in the balcony.


“Our top priority was to preserve the existing acoustics,” Corry said, “which is part of the reason the project design for the balcony level is focused on seating replacement, which will not have a major impact on the acoustics. The side walls and ceiling shaping that provide the sound reflection pattern to the balcony seats will remain the same.”


Acoustic Enhancements

Testing and interviews with musicians and staff revealed potential for improvement for the acoustics on the main floor. The acoustic model was used to confirm the proposed design solutions, which include adding low profile curved walls near the stage that will provide additional reflections from the stage to main floor audiences.


“Architects at Snøhetta and Christner [the project’s lead architecture firm and architect of record, respectively] worked closely with us to incorporate these new acoustic elements without compromising the aesthetic of the room or encroaching on the new seating layout,” Corry explained.


The SLSO took great care in confirming the impact these new elements would have on the acoustics of the space. Kirkegaard and the BSI Construction team created full-scale mockups of the shaped walls using lightweight and low-cost prototypes, which were lifted in and out of place during a special orchestra rehearsal, while musicians and staff listened carefully to the difference. Corry said the increased support was immediately noticeable.


“We got feedback that the sound from the orchestra in the middle of the auditorium was much clearer and more present,” he said.


Reshaping the new rear wall at the back of the main floor will also help diffuse soundwaves better, enveloping main floor audiences in sound and reducing distracting sound reflections to the musicians on stage.


Minimizing Distractions

While architectural adaptations to the auditorium will be the most visible way the acoustics will change, Kirkegaard also recommended ways to reduce the intrusion of outside noise into the hall.


The rear wall of the main floor level will move forward several feet and an additional set of doors will be added to create sound vestibules as a buffer zone between lobby spaces and the concert hall.


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Brian Corry, St. Louis-based Partner at the acoustics firm Kirkegaard.

“Once the renovation is complete, the lobbies can remain active while there's a concert happening without concern for noise disrupting the performance,” Corry said.


Exit doors on the north side will be replaced with acoustically rated doors that will significantly, though not totally, reduce external sound produced by traffic on Delmar and Grand Blvds.

Another consideration will go almost unnoticed by most patrons—controlling the background sound created by HVAC, electrical, and plumbing systems.


Much of Powell Hall’s mechanical systems were under the auditorium floor. Musicians noticed equipment noise on stage, and many systems had to be turned off when the orchestra recorded music. Kirkegaard worked with the design team to select quieter, more efficient systems. And much of the equipment will be relocated to the basement and roof of the new backstage expansion.


The result, once Powell Hall reopens in 2025, will be a welcome return to an acoustic cherished by audiences for decades, fortified and enhanced for generations to come.


“Powell Hall has a soul,” Denève said. “A strength of this hall is that you have a feeling it adds a certain glow to the sound with its distinct character. I am so happy that this renovation will add to Powell Hall’s poetic sound.” 

 

 

Eric Dundon is the SLSO’s Public Relations Director.

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