Pardon my reverb

Jennifer Oullette in her always excellent blog, Cocktail Party Physics:

WcsabineThe father of modern architectural acoustics is an American physicist named Wallace Clement Sabine. In 1895, he was a lowly faculty member of Harvard’s physics department, who was handed the knotty problem of improving the infamously bad acoustics of the university’s Fogg Lecture Hall, part of the recently constructed Fogg Art Museum. Sabine didn’t have any particular expertise with sound — he didn’t even hold a PhD (the horror!) — but he doggedly tackled the challenge  as he would any other physics experiment. He spent several years studying the acoustical qualities both the museum’s lecture hall, and the Sanders Theater, widely considered to have excellent acoustics, in order to determine  what might be causing the difference in sound quality.  Specifically, he was attempting to find some objective formula or standard by which to measure and assess the acoustics of performance space designs.

It wasn’t an easy task because so many variables had to be taken into consideration. He and his assistants tested each space repeatedly under varying conditions, moving materials back and forth between the two halls — such as hundreds of seat cushions from the Sanders Theater — and making careful measurements armed only with an organ pipe and a stop watch. He timed how long it took for different frequencies of sounds to decay to inaudibility under those varying conditions: with and without Oriental rugs, various numbers of people occupying the seats, and so forth.

Ultimately, he was able to determine that there was a definitive relationship between the quality of a room’s acoustics, the size of the chamber, and the amount of absorption surfaces that were present. And he came up with the formula for calculating reverberation time, still the critical factor for gauging a space’s acoustical quality…

OdeonThe field of concert hall acoustics has advanced far beyond Sabine’s rudimentary first measurements, although there are still purists who believe that there will always be a subjective element that eludes attempts at strict mathematical description. Nonetheless, using just those sorts of quantifiable tools, Leo Beranek, one of the most eminent acoustic engineers, has identified three basic aspects to achieving a sufficiently good sound in a concert hall: (1) Listeners should be as close to the orchestra as possible; (2) Listeners should have a line of sight to the orchestra so the sound can travel unobstructed; and (3) the interior surface of the hall should be made of a hard material so that sound energy is not absorbed or lost. So an acoustical consultant needs to balance strength, reverberation and clarity requirements when designing a performance space.

Computer modeling has become one of the modern acoustician’s most important tools. It turns out that the sound diffusing through a performance space can be modeled as particles of light bouncing around that space, much like a billiard ball bounces around a table in response to being hit by the cue.

More here.