by MICHAEL BOWEN & r & & r & & lt;span class= & quot;dropcap & quot; & T & lt;/span & he rear interior wall of the Fox -- back there behind the last row of seats in the balcony, 120 feet from the lip of the stage -- is now covered in Fiberglas wrapped in two inches of special fabric. The wall has a slightly concave shape that, for structural reasons, couldn't be changed.

All the fabric must be so the folks up in the balcony will be able to hear better, right? Not exactly, say the project's acoustical engineers. Concave surfaces focus sound like a prism. All the refashioning of the back wall was aimed at helping musicians onstage hear one another better.

In rough terms, it takes about a quarter-second for a blast of orchestral music to hit the back wall -- and just as long to return. That would create a disorienting half-a-second-later reverberation for the violin and brass players. Hence the swaddling of the back wall.

"We call that 'slapback,'" says Robin Glosemeyer Petrone, a design principal with the nationally recognized acoustical engineering firm JaffeHolden and the project manager for the years-long process of ensuring the acoustical quality of Spokane's Fox Theater.

& lt;span class= & quot;dropcap & quot; & L & lt;/span & aypeople don't really understand what acoustical engineers do. "Half think it's black magic, that we don't have any science," Petrone says. "Half think it's all science. But it's really a balance of the two."

Furthermore, she says, not only is every theater unique, but listeners prefer different acoustical features: "Some like it more 'swimmy.' Some like it with more clarity. And the performance requirements, from Beethoven to Brahms, are very different."

The engineers' attention to detail is impressive: installing special gaskets around the fire doors; permanently sealing the roof hatches; cushioning generators with vibration isolators; tunneling under the seats to widen air ducts and reduce that "whooshing" sound; adding exit gunnels ("mushrooms") for air flow, also under the seats; calculating the amount of sound diffusion created by the ornate organ recesses on either side of the Fox stage; tuning the hall during break-in rehearsals to determine whether the cellos sound better on risers -- and whether the woodwinds sound better on higher risers; experimenting with the angle of individual pieces of the orchestral shell; adding another 15 feet to the front of the stage and steepening the slope of both the lower and upper seating levels, to "pull the orchestra out into the room" and improve reverb times; selecting the kind of wood for seat backs and foam for seat cushions that would achieve a balance between too much sound absorption and too much reflection. (To acoustical engineers, the people who sit in those seats are just sound absorbers.)

The result of all that renovating and tinkering? In a nearly deserted Fox, there's the kind of hush associated with churches: an urban refuge, with plenty of attention paid to noise suppression. Fire engines with sirens blaring will be able to race past the Fox without disturbing concertgoers' listening.

And Petrone knows exactly how such results were obtained. "We held the line on duct sizes," she says.

Spokane Folklore Society's Valentine's Dance @ East Spokane Grange

Sat., Feb. 11, 7-10 p.m.
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