Acoustic Shells in Performance Spaces

Like any other tool, a large venue performs best when it is put to the use for which it was designed. Extending a venue's program is, by nature, a compromise. 

But large concert halls must do so much more than host concerts. They are often flagship gathering spaces, central to the culture of the institutions supporting them. Even when concert halls are designed and tuned for, say, orchestra concerts, they invariably play host to many other types of events—lectures, screenings, public conversations, readings, amplified music performances, donor events, graduations…even dinners. With the exception of major international performing campuses like New York’s Lincoln Center, or major music schools like the University of Indiana Jacobs School of Music that are privileged to have a suite of performing venues, institutions often only have one large venue.

Some large venues are created with specific performing forces in mind, like orchestras. Some are designed to be multi-purpose venues intended to support music, dance, theater, opera, etc., even though the specific needs of each of these performing agendas are quite different.

In either scenario, large venues often function less well when used by soloists or small groups of performers.

They can feel out of scale and cavernous, swallowing the individual performer, whose sound and presence seem to disappear from the stage rather than radiate from it. But there are compelling economic and practical reasons that prevent headlining solo violinists from performing in the 150-seat venues that would be acoustically best suited to their instruments.

This is where acoustic shells come in. 

One variety of full-stage acoustic shells is specifically designed for use on multi-purpose stages. They are intended to mitigate the acoustic problems created by prosceniums, fly spaces, wings, and curtain riggings. The shell sits well in front of the upstage wall and curtains, reflecting sound forward and bringing the stage closer to the arrangement of an “orchestral stage.” On the opposite end of the spectrum, small, movable acoustic shells can be added to virtually any stage to support the sound of soloists and small groups of performers, essentially creating a nested “stage within a stage.” 

Full-stage shells can nudge the multi-purpose venue closer to realizing the dream of “one venue/many performances,” but they come with large price tags, huge storage footprints, and significant time commitments to install on stage and remove back to storage. The sheer mass of these shells forces a production schedule onto the venue that chooses to use them.

Smaller acoustic shells tend to be marketed as budget options. They are often modular, which can be good for reducing their storage footprint, but less good for their set-up time. And they are often built as light-weight as possible, which means they offer less robust acoustic support. Being mass market offerings, their generic nature can look out of place on an otherwise artfully designed stage.

Are there other solutions? Certainly. We’re familiar with two venues that recognized this suite of issues early on and built “permanent acoustic shells” into their mid-size stages.

The 496-seat Warner Concert Hall inside the Oberlin Conservatory (built 1963), has a wing-shaped acoustic wall embedded in the center of the stage. It stores beneath the stage and can be mechanically raised into position when needed. It is accompanied by two large, rolling towers that complete the look and make the nested stage space fit the look of the entire venue. 

The 475-seat Reva and David Logan Center for the Arts at the University of Chicago (opened 2012) incorporates a rolling acoustic wall that stores in the upstage wall and can be pulled forward for smaller performing forces. Both of these built-in solutions are examples of what’s possible when the architects and designers consider a range of acoustic possibilities early in the process, and it’s interesting that both examples exist in  venues of ~500 seats. 

A better stage within a stage

Recurve acoustic shell, originally conceived by Larry Kirkegaard and revived in a collaboration between acoustician Zackery Belanger and industrial designer Michael Hahn, was designed to bridge the enormous gap between mass-market modular shells, and the fully incorporated shells like those at Oberlin and UChicago. 

Three primary goals guided the design process: 

• Fastest possible setup 

• The trifecta of: fullest possible stage coverage, most compact storage, and practical transportability 

• Maximum acoustic support 

Here’s how we did it.

Fastest possible setup

While modular designs offer a degree of customizability according to the needs of the venue, they also demand that the shell is constructed and deconstructed every time it is used. To maximize setup speed, Recurve needed to be a single, rollable unit, able to be handled by one person.

The trifecta of fullest possible stage coverage, most compact storage, and practical transportability 

To solve for this suite of issues, we settled on a scrolling panel design. Fully open, Recurve stretches 40 feet across a stage. Coiled for storage, its footprint is only 7 feet x 2 feet, or roughly one-third that of a concert grand piano. The height was limited to 6 feet so that it could easily roll through a standard doorway.

Maximum acoustic support

Low frequencies need mass to reflect. This is another disadvantage of light-weight of modular shells—they can tend to make the performers in front of them sound too bright and brittle. The scrolling panel design meant that we could engage heavier materials. We settled on a honeycomb core panel construction to achieve the stiffness, mass, and dimensions necessary to support the full frequency range of acoustic performance. But mass isn’t everything. Recurve is also precisely curved to maximize the important influence of early sound reflections.

Watch a side-by-side comparison of a sound wave expansion on a stage with Recurve and without.

The original concept for Recurve came from famed acoustician Larry Kirkegaard, who envisioned a graceful, agile, single-unit acoustic shell that could be set up easily and divide a stage for a range of activities. He designed a prototype of the acoustic shell he imagined in Aspen, Colorado, to prove the concept. 

A musician's perspective on acoustic shells

To learn more about a musician’s experience with performance hall acoustics and acoustic products, Umbel interviewed French horn player Adam Unsworth. Adam is Professor of Horn at Northwestern University Bienen School of Music. He has been a member of the Ann Arbor Symphony Orchestra, Philadelphia Orchestra, and Detroit Symphony Orchestra. Over the course of his career, he has played with many orchestras, chamber and jazz ensembles, and as a soloist. 

What makes a for good acoustic experience in a performance hall? 

Primarily, feeling like my own sound is resonant and pleasing. It’s hard to enjoy a performance or rehearsal if I don't like my own sound, and I’ve played in halls where my sound feels small, and it feels hard to project to the audience. Secondly, being able to hear my collaborators in detail, to really hear the details in tone and color, and the core of my sound so I can tune with them.

What are the specific acoustics challenges of your instrument? 

The French horn is the only instrument in the modern era whose sound is emitted backwards when the musician is facing the audience. Because the bell faces backwards, the French horn’s sound is not one that people are accustomed to hearing in a direct way; they are used to hearing it after it has bounced off a couple of surfaces.

French horns need reflective help to be able to balance with forward-facing instruments, particularly other brass (trumpets, trombones, etc.), or we need to be conscious of the angle of our bell in our seating choice. We have to think about directional playing, which can involve arranging seating in a way to direct sound comparable to other instruments.

In a recital situation (when playing with piano accompaniment), French horn players will stand while playing and point their bell at the piano lid fully open, using the lid as a reflective surface to get the sound into the audience more distinctly. This can help to hear the clarity of the articulation and tone. 

What is your experience with acoustic shells and how they affect your performance?

I take advantage of shells. Especially having played in many different halls, I know it can make a significant difference on a problematic stage. Most stages that were built with a multipurpose intent, such as including both theater and orchestra, need these panels in some way.

I have been in dress rehearsals while the stage crew adjusts the acoustic panels because the musicians are having a hard time hearing each other. The stage crew tries other configurations of panels to optimize the acoustic quality. In some instances, French horn players will ask for panels to be put behind them to make sure their sound reflects out to the audience. In other cases, horn players request a personal reflective panel to project sound out to the audience. These personal panels are not always available and are not necessarily preferred because the sound is so immediately reflected back at the musician, but horn players will often use these panels if they are the best option, because it’s better than not being heard at all.

Tell me about some challenges you have faced on stages that don’t suit the ensemble.

The transition from rehearsing in a small room to a concert hall, which is common for chamber groups, can present challenges in adjusting to a drastically different acoustic environment. Chamber ensembles usually rehearse in smaller rooms, like teaching studios or classrooms, which have lower ceilings and walls that aren't very far from the musicians. The ensemble will then go to perform in a concert hall with drastically different spatial proportions, affecting the balance established in the rehearsal room. Chamber ensembles ideally have a dress rehearsal and sound check in the hall before a performance to be able to recondition and adjust their ears because the concert hall setting is so acoustically different from what they’re accustomed to in rehearsal.

In a worst-case scenario, it's difficult enough to hear from your colleagues that you have to do a lot of physical cueing. Normally, part of playing in a chamber music ensemble is watching the other musicians, but in a difficult acoustic environment, a lot more physical action needs to be taken for musicians to hear each other. This can make the performance experience less enjoyable, and you don't get a great sense of the product and how you’re going to sound to the audience in terms of balance and blend. 

Ultimately, an ensemble’s perception of resonance and clarity in a concert hall can have long-term impacts for the musicians and orchestra.