The filmmakers featured at the Sundance Film Festival® have worked hard to weave sound and image into stories that transport the audience. With only so many bona fide cinemas in Park City, Utah, Sundance—and festivals like it—often must screen films in places that were never intended for that purpose.

But high school gyms, community centers, and concert halls don’t have projection booths or upholstered seating; and they rarely have much more than public address systems. Under these circumstances, the environment can make or break the filmmaker’s spell. So chairs can be staggered to improve sight lines, and digital cinema projectors—quieter and more portable than conventional film projectors—make it relatively easy to address the visual aspect of a screening. Sound, however, is harder to tackle.

The critical factors:

  • Room shape. Width, length, and height influence how and where sound travels.
  • Surfaces. If they’re all hard—wood floors, concrete walls—then the film’s sound will be unintelligible.

If time permits, consultants can take some measurements. RT60 is the standard for gauging reverberation time (RT), the amount of time it takes for a tone to “decay” 60 decibels—more or less to silence—in a room. Low-frequency sounds, for example, have longer wavelengths and are less likely to be absorbed by room surfaces, so they take more time to decay to silence. RT60 measurements are taken at multiple frequencies across the spectrum, but mid-range frequencies are the most meaningful because the ear is especially sensitive to those middle frequencies.

Consultants use special software and microphones to take these measurements. The measurement may be scientific, but the microphone placement is an art, requiring the mics to be placed in an off-axis parallelogram that’s large enough to collect information in the prime seating area of the room. (But if the parallelogram is too large, the frequency response measurements will take too many aberrations into account, leading to a speaker configuration that delivers mediocre sound when the film is shown.) Although most rooms require four or five mics, as many as eight or twelve might be needed for a space as large as the orchestra parterre of the Dolby® Theatre(SM), at more than 9,000 square feet.

Or, if you’re a seasoned professional working under deadline, you might just size up the effects of surfaces and room dimension by doing a quick visual scan and clapping your hands. There may be little time to do much else, but it’s enough for Dolby experts to gauge what needs to be done when asked to help in Telluride, Toronto, or Berlin.

Follow #sundance on Twitter to find out what’s going on at the festival—from Dolby and anyone else in Park City.

[Photo credit: Wikimedia Commons]