- Dave Conant
Two More Acoustical “Two-Fers”
By: David Conant, FASA, MCH Principal
As we noted in our August 2022 blog, designers especially enjoy solutions that solve several issues in a single stroke. While the takeaway remains the same, here, we describe novel performing arts solutions. These designs yielded multiple, cost-effective and surprisingly effective benefits.
Jensen Grand Concert Hall at Stevens Performing Arts Center
The architectural design aesthetic for this center at ISU in Pocatello, Idaho was to follow the neo-classical style and as such, its 1200-seat concert hall would provide a clean yet articulated ceiling. A great amount of variability in the hall’s reverberance was required. However, due to the architectural style, the typical absorptive drapery tracked across an obviously blacked-out cavity above cloud reflectors was infeasible. The objectives were to rapidly vary the occupied mid-frequency reverberation time (T60) within the audience from somewhat over 1 second (small jazz groups and lecture) to 3 seconds (pipe organ and choral works) and also nuance the on-stage acoustics for the musicians’ aural needs there.
Acoustics for Patrons in the Audience Chamber
As for most passive variable acoustics projects, we established early-on the appropriate room volume, approximate shaping and surface finishes that could achieve the maximum desired reverberance then sought means of decreasing effective room volume and increasing sound absorption since both determine a hall’s T60.
With a bar napkin in hand, we sketched up a novel variable acoustics concept that seemed might have traction in providing sufficient “effective” volume reduction while simultaneously increasing sound absorption. Thus, a clear “two-fer” - IF it would work. Well…. a fine variation engaging a motorized pentagraph certainly did!
Field measurements demonstrated that these devices (3 each, audience left and right) change the hall’s T60 by a full 1-second. Additional reduction is available by deploying absorptive drapery behind rear audience and high above the performance platform canopy. The “occupied” mid-frequency T60 range is approximately 1.4 to 3.0 seconds. These devices are so effective because they interact with propagating sound waves by increasing absorption while interfering with the free propagation of soundwaves, thereby reducing acoustically-effective room volume.
Acoustics for Musicians On-Stage
It is especially important that musicians clearly hear each other’s nuance of timing, blend, and attack cues, all of which are so vital to optimizing the ensemble. If those components aren’t made right on-stage, they certainly won’t be right within the audience.
By simply reimagining this performance platform’s upstage wall, abundant variation in on-stage acoustics became possible. The upstage wall comprises five mobile recital screens. When stored, these provide excellent shaping for supportive reflections, as is particularly useful for full orchestra. Downstage, these can be arranged to best accommodate smaller ensembles. When removed from self-storage, the upstage cavities provide either enormous sound absorption or reflection, as desired.
Thus, this concept for adjusting on-stage acoustics, provides in a single stroke, highly mobile recital screens that:
form an acoustically articulated upstage wall while simultaneously “storing themselves."
may be arranged in whatever format best suits to the ensemble.
provide within their self-storage cavity an upstage wall either highly sound absorptive or highly-reflective.
provide within this same cavity, readily-accessed storage for additional highly absorptive panels that may be mounted at stage left and stage right.
Summary
“Two (or more)-fers” occasionally arise by intentional force of logic. Far more often they’re the result of a natural and unintentional juxtaposition of disparate needs. Scribbling helps us subconsciously make these juxtapositions evident. As it does, inevitably the practical and engineering mind may say, “Yeah, but…”. Challenging that natural practical response can develop both counterarguments and sometimes an insightful, optimized two-fer!
