Making sound decisions

As the Segerstrom Concert Hall nears its debut, its sophisticated acoustical system is getting a workout.

by Timothy Mangan / The Orange County Register
August 27, 2006

Damian Doria is the ringmaster at the new Renée and Henry Segerstrom Concert Hall. As president of Artec Consultants, the company behind the sound design of the venue, and as principal acoustician on the project, he's the man in charge of the hall's state-of-the-art adjustable acoustics, a rather amazing series of bells and whistles that can radically change and subtly hone the way the hall sounds. Wearing jeans and sneakers and a dark dress shirt and sporting a trim beard and wire-rims, Doria looks more like a friendly college professor than circus leader, but give him a top hat and cane and he'd certainly do just fine.

Step right up, ladies and gents (he might say), behind those doors to your left we have the mysterious reverberation chambers, where sounds go to invisibly rejuvenate. Look, over there, those luxurious curtains are no ordinary decorative draperies, but magical sound soaker-uppers of voluminous velour. Overhead, do not be afraid, that's not a flying saucer with aliens inside, but an acoustical canopy, capable of sending sound beams to wherever we like. Be careful, don't get too close.

Yes, this is no ordinary concert hall. It's designed especially for symphonic music but also to be flexible enough to use for other types of events. In the past couple of weeks Doria has begun the sophisticated maneuvers involved in "tuning" it. Sitting in on the Pacific Symphony's rehearsals, talking with the musicians in the orchestra and conferring with conductor Carl St.Clair, he's not only finding out how the hall sounds, but also testing and arriving at various settings for the acoustical mechanisms that will serve the music as well as the musicians' aural tastes and needs.

On a recent evening, just before rehearsal, he showed a group of reporters just how the adjustable acoustics work. The technical lingo flew thick at times, and Doria spoke quickly, almost urgently, as if he were describing a new toy. Luckily, a tape recorder caught what he said.

The room is dominated by the acoustical canopy, a giant, silver, orbicular contraption that hangs on cables between the high ceiling and stage floor.

"It does a lot of things," Doria explains. "It reflects sound. The reason why we just don't let the sound go all the way to the ceiling is that the strings in particular could use the support of a surface that's closer than all the way up at the ceiling. The reason why the ceiling is so high in the first place is to create sort of the acoustic head room or space for louder passages in symphony work. That helps to prevent distortion - during those triple fortes - that is common in halls of smaller volume," of which Segerstrom Concert Hall, with its 2,000 seats, is one.

The canopy is divided into three separate sections, each adjustable and each one hanging above, roughly, the three sections of an orchestra and chorus - the strings; the woodwinds, brass and percussion; and the chorus. By manipulating the height of the three sections as well as the gaps between them, Doria is able to affect the way the musicians hear themselves onstage, as well as the way the audience hears them.

"The gap between that (first) canopy and the next one," he continues, "especially if they're not set at the same elevation, makes a difference in how it supports the brass and winds as compared to the strings, because if it's a fairly large gap, then a lot of the wind and brass sound goes up through the gap, as opposed to being reflected if the gap is very tight."

Already, several settings of the canopy have been tried. How was the setting different on this night than it was for the orchestra's first rehearsal, last Friday, we ask?

"It's about two and a half feet higher in the front canopy and then the gaps between the canopies are half of what they were. This is the result of not only what we heard on that Friday, but also of working with Carl and the orchestra yesterday. We came in and we raised the canopy about five feet and kept the spacing between the canopies at three feet per step, and we decided to lower that spacing to 1.5 feet per step, to see what the impact of that was. And the orchestra really liked it with smaller gaps between the canopies. Then Carl and I discussed lowering the canopy again, all three pieces, about two and a half feet, to bring it halfway closer to what we had. So now we're at 44 1/2, 46 and 47 1/2 feet."

This kind of tweaking can go on forever, of course, and perhaps will. The canopy settings will differ depending on the kind of group performing (string quartet, solo piano, chamber orchestra or full symphony) and the individual musicians' preferences, so Doria is glad to have these few weeks to experiment a bit before the hall opens on Sept. 15. When rehearsal finally did begin on this Monday night, a listener could hear a difference in the way the orchestra sounded compared to the previous Friday. On that day, the violins seemed to have a pronounced bloom and advantage over the rest of the orchestra; on Monday, that advantage had narrowed and balances between sections evened. But Doria reported that St.Clair wasn't quite happy with this setting either, and yet another would be tried.

IT'S ALL IN THE REVERBERATIONS
After explaining the uses of the canopy, Doria escorts us into one of the reverberation chambers, painted a deep blue. The tall, narrow chambers (there are four of them) run from floor to ceiling along both sides of the hall, and from choir level to ceiling on the two back portions of the stage. They amount to separate rooms, isolated from the main concert hall by a series of airtight wall panels, or chamber doors. But the idea isn't to keep them closed.

"As you open the chamber doors," Doria explains, "it allows some of the (sound) energy of the room (the concert hall) to escape. So the reverberation time, the decay of sound in the main room, becomes shorter in that room itself, because you're letting sound out as though it's being absorbed."

It doesn't stop there, though.

"Basically, that energy comes into the secondary chambers - these coupled reverberation chambers - and creates reverberance in these chambers. ... Sound will reverberate in here, and then it goes back into the main hall."

All of the chamber doors can be opened in increments, anywhere from 0 to 90 degrees. Depending on how many doors you open, where those doors are (at the top, middle or bottom of the hall), and how wide you open them, you can change the sound in the main hall in a variety of ways. For instance, if you were to open all of the doors all the way at the same time, you could (if you wanted to) make the sound less clear and distinct, since, with the doors wide open, there would be fewer reflective surfaces in the hall itself for the sound to bounce off of.

"But then by level," Damian says, explaining the use of the doors at different heights: "If you adjust the lowest levels (of doors) around the (stage) platform, that tends to energize the chambers a lot. Because the sound energy reaching those doors is considerable. Whereas, if you open up the top of the chamber (near the ceiling), all you're energizing that with is sort of the ambient reverberant field in the main volume.

"So the type of sound that reaches the chambers, the level, the blends of sounds that reach the chambers, is different depending on what levels you're opening."

The possibilities are endless, it seems, but the main idea is to have a way of controlling the reverberation in the main concert hall. With the doors open in certain ways, Doria says, he can clarify busy orchestral textures or loud passages. The sound can have a sharper initial decay, but a longer sustained reverberation, the former improving the clarity of tone and the latter improving its beauty.

NOT MERELY DECORATION
In the days and weeks to come, Doria will undertake objective tests of the concert hall. With calibrated microphones in place, he'll "excite" the room with low- and high-frequency bursts of sound. He'll send specially created white noise into the space, and may pop a balloon or two. A computer will measure the results, supplying all sorts of technical information about how the hall responds. One of the tests will allow the proper phasing of the loudspeakers in the hall. But all of them are secondary to subjective human ears, says Doria. These objective tests don't measure the same things humans hear anyway.

As our now somewhat dizzy group proceeds, Doria leads us to a rectangular hole in the wall of the second floor. Inside, on motorized tracks that lead along the top of the outer wall, are curtains, made of two layers of thick, tan velour. These are 32-ounce stage velours, he tells us, "which gives us good low-frequency response - they soak up low frequencies as well as they do mid and high frequencies. If you go to a lighter-weight velour, it tends to not absorb frequencies below 250 hertz (just below middle C on a piano) as well as it does above."

But why would you want to soak up any frequencies in a concert hall designed to make them reverberate in the first place? The quick answer is that the curtains, which can be deployed for the length of the hall on every level, will be used mostly for amplified events, such as pops concerts and lectures, where the sound of the hall needs to be deadened for more effective use of the loudspeakers.

But the curtains will also probably be used - in much smaller doses - for non-amplified classical events. One such deployment was tried during the rehearsal. With the canopy at its designated height for the day, Doria estimated that he was getting about 3 seconds of reverberation. After a quick conference with St.Clair, he decided to bring out a section of curtains on the fourth floor, above the canopy and behind the orchestra, and asked a technician to do the job.

"The area above the canopy is like a little captured volume that tends to add a lot of reverberance to the late field," he said. Once in place a few minutes later, the curtains made the sound of the orchestra tighter, more focused, and the reverberation in the room was reduced, Doria estimated, from about three to two and a quarter seconds.

With this kind of power at his fingertips, it's no wonder that Doria often wears a satisfied smile.
By all accounts, the Pacific musicians are satisfied as well, thrilled with the sound and flexibility of their new hall. Those few listeners sitting around late into the evening seemed so too. One of them tells Doria that he thinks the woodwinds sound especially good.

"Thank you," he says, grinning. "I play flute. I made sure they were taken care of."