- Dave Conant
Acoustical “Two-Fers”
By: David Conant, FASA, MCH Principal
Designers enjoy solutions that solve several issues with a single stroke. Some select acoustical solutions that arose over the past 35 years resulted from a modest bit of napkin sketching, while others capitalized on novel application of technology. Each yielded cost-effective, much appreciated, and often unexpected, benefits.
Phoenix Symphony Hall Renovation
The renovation of this venerable 2,300seat venue was not intended as an “acoustical renovation.” The charge to us was, “Just don’t make it any worse, acoustically, than it already is.” The audience chamber required a substantial overhaul to meet ADA requirements, and a more energy efficient HVAC system was to be incorporated.
HVAC return air noise was far too loud. The immutable physical path immediately behind the sidewall registers caused excessive airflow velocities and significant noise, even at minimum air quantities. Our studies also revealed an absence of beneficial sound reflections from sidewalls because the existing large return air grilles precluded useful sound reflections.
The solution: Tall, carefully shaped cowlings with sound-absorptive inner facings and open tops were designed to block and absorb the return air noise, while also re-directing stage sound laterally across the audience, resulting in much-improved immersion in non-amplified music.
Angelus Temple Renovation
The client goal was to uniformly provide excellent contemporary music at up to 118dB(C) as well as good speech intelligibility to all 3,000 seats in this iconic (1923) Los Angeles building. However, the large dome ceiling created severe sound focusing at the balcony mix position, and was a primary contributor to the room’s 13-second reverberation time. The National Park Service required the large overhead dome to remain visually unobstructed, and structurally, the dome could not support any new load, such as for sound absorbing or diffusing elements.
A physical laser-light scale model (shown below on lower left image) was constructed to test various baffle concepts involving large, sound-absorptive and scattering panels that would still leave the dome visually unobstructed.
The solution: 64 sound absorptive baffles hang from cables attached to the compression ring supporting the edge of the dome. The baffles are uniquely positioned to intercept sound from the chancel loudspeakers on its way up to, or back down from, the reflective dome; they block, absorb, or scatter essentially all of the sound waves in their direction. Their presence resolved the problematic focusing at the balcony mix position, while dropping the room’s reverberation time from 13 seconds to 1.6 seconds. Both and music and speech intelligibility requirements were met beautifully, while addressing structural needs and aesthetic requirements of the National Park Service, and even enhancing the dome’s visual drama.
Summary
Oftentimes design challenges can lead to creative and elegant solutions that yield several benefits. Examples of two successful "two-fer" solutions were discussed, including cowlings that reduce airflow noise and improve lateral reflections, as well as sound absorptive baffles that respond to several challenges, such as focusing, reverberance, and historical requirements. "Two-fer" solutions can address many concerns, leaving clients and end-users especially grateful!
