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Concert Hall Acoustics, with Dr. Cyril Harris

JPG photos of this meeting

Written by Gary Louie, AES PNW Secretary

September 20, 1999 at Benaroya Hall Music Center

A Joint Meeting of the: On September 20, 1999, Dr. Cyril Harris, noted acoustician and Professor Emeritus of Architecture at Columbia University, spoke to a combined meeting of the Acoustical Society of America, the American Institute of Aeronautics and Astronautics, and the Audio Engineering Society in the S. Mark Taper Auditorium at Benaroya Hall, Seattle WA. Dr. Harris was responsible for the remarkable acoustics of this new concert hall. Now entering its second season, the hall has received justly deserved praise for its acoustical properties. Nearly 200 people attended.

Dr. Harris grew up in Hollywood in the early days of the talkies. His junior high school was located across the street from the Warner Bros lot. "I'd get in there by various means," said Harris, "and I found out that to avoid any problems, they routinely changed the batteries that powered much of their equipment even when they been used very little. They couldn't afford to risk any breakdowns. These were very expensive units, but they'd let me buy them for 15 cents apiece. I was an amateur radio operator, and I'd build my own amplifiers for music reproduction, and I guess I got an early start in acoustics through that - and those Warner Bros batteries." He got his BA and MA degrees at UCLA, later moving to Massachusetts to study for his PhD at MIT under Phillip M. Morse ("the best acoustics theoretician in the world"). After the war, he worked under Harvey Fletcher at Bell Laboratories followed by a Fullbright Lectureship in Holland and a stint with the Office of Naval Research in Europe. Returning to the US, he then traded places with Harvey Fletcher at Columbia University (Fletcher wanted to return to BYU in Utah).

At Columbia, Harris started the Acoustics Laboratory of Columbia and engaged in government-sponsored research as well as studying various acoustical odds and ends. Over the years, Dr. Harris has worked on noteworthy concert auditoriums such as Abravanel Hall in Salt Lake City, the Met in New York and the Krannert Center in Urbana, IL. He brought acoustical success to Avery Fisher Hall in New York City.

Dr. Harris was awarded the Franklin Medal, 1977; the Wallace Clement Sabine Medal,1979; the A.I.A. Medal, 1980; the Gold medal, Audio Engineering Society, 1984; the Gold medal, Acoustical Society of America, 1987. He is a member of National Academy of Engineering and the National Academy of Sciences.

Dr. Harris opened his Seattle lecture with some open questions:
- Why did they build such good halls in the past, and now that we have acoustical consultants, why are some halls notable as acoustical disasters?
- How did the ancient Greeks and Romans build such good 5000 seat theaters, and today we marvel at building a decent 2500 seat hall?

Dr. Harris, armed with many slides, then dove into "Concert Hall Acoustics 101."

He started with ancient Greek and Roman theaters. All of his students should be able to build a decent simple auditorium or a Greek theater after his class. He described the fundamentals of open air theaters.

In a theater, a sound source on stage has an absorptive surface between the listener and the source - other audience members. If the plan is flat, on one plane, it's like snow on the ground - a great sound absorber which causes a phase change of the sound over the absorptive surface which interferes with the direct sound at the listener. Next, raising the source or raising the seats gives more direct sound (with less phase-changed absorbed/reflected sound) to the listener.

He showed a slide of Epidavros, the famous ancient Greek open air theater, and Roman theaters. Roman theaters added a stage reflector, with diffusers - irregular backwall surfaces. A flat wall would reflect sound at only one angle. Irregular reflectors reflect sound in many directions, to many people. Dr. Harris then used a flashlight to highlight the irregular surfaces on the orchestra shell around him used to scatter the sound.

He posed the question: Many people say that the acoustics are perfect in Epidavros, why can't he do that? He says this is not a valid question. People visiting Epidavros never try speaking off axis, and never with a full audience of noise sources. We can do acoustics just as well or better today.

Dr. Harris described Odea - the first ancient enclosed theaters. The name "Odeum" means "a place of singing." Singing sounded good in an enclosed space because of the reverberation. It is not so good for speech, however. Benaroya Hall was designed with a reverb time appropriate for the symphony orchestra. A sound reinforcement system that directs sound to the audience is helpful for speech.

Next, Dr. Harris described the basics of creating proper reflections and diffusion in halls. Physics dictates that the angle of incidence equals the angle of reflection for a wave, if the reflecting surface is large compared to the sound wave. Designers often get into trouble when they forget that the surface must be large compared to the wave. He recounted the history of formulas used for estimating reverb time, especially the work of Wallace Sabine. Again, the formula can only apply when the interior is all diffuse. Some designers try to use the formula when it doesn't apply.

He showed a slide of the famous Grosser Musikvereinssaal in Vienna, perhaps the most lauded concert hall in the world. It is shaped like Benaroya and has a similar reverb characteristic, but Benaroya has better clarity, he stated. There is a lot of ornamentation in the Grosser Musikvereinssaal walls and it has a coffered ceiling to scatter sound. Pay close attention to the size of the surfaces used to scatter and diffuse, he warned, as they only work at certain frequencies. You need various sizes to cover the needed frequencies. Diffusion is good because when you are hit by sounds from many directions, you feel immersed in the music. He thinks the reverberant quality is very uniform throughout Benaroya.

A modern problem is finding ways to get lots of diffusion without using baroque/rococo architecture elements. Some newer architectural styles dispensed with ornamentation completely, and those halls sounded bad - they had no diffusion. Benaroya's ceiling for example, is coffered with multi-sized surfaces on inverted pyramids for reflecting. It was unusual to have the architect, acoustician and music director work together as on Benaroya. Even the organ needed to be done right. Royal Festival Hall in London is an example of an acoustic problem caused by the organ placement. Acoustic reflectors were placed above as a fix, but they aren't big enough to be very effective.

Dr. Harris showed slides of past projects he drew ideas from: the National Academy of Sciences in Washington DC; the Metropolitan Opera House in NY (his first big job); the Kennedy Center opera house; Krannert Center in Urbana; Abravanel Hall in Salt Lake City; the National Center for Performing Arts, Bombay India. In Bombay there were problems fitting cast panels, requiring trimming. In Benaroya, computer controlled cutting was used for the 2,400 wall panels. A slide of Philharmonic Hall at Lincoln Center (NYC) was shown. It was a bit of a scandal because the sound was so poor. Major revisions were made by several people, with changes to chairs and walls. One of the original problems was that the diffusers were all one size (a grave error). It needed different sized diffusors all around.

Many questions from the audience were posed. (Questions and answers are paraphrased)

Question: Are scale acoustic models useful?
Answer: Only if you know nothing, it might prevent gross errors. It won't tell you if the hall will sound good.

Q: Considering the train and bus tunnel under the hall, how did that affect the Benaroya design?
A: It cost money to isolate the hall better ($1-2 million more). When the Sydney Opera house opened you could hear the toilets flush. It was very expensive to fix that.

Q: At Avery Fisher Hall, there was a battle with the fire marshall about the air gap under the wooden floor. Was there a similar problem in Benaroya?
A: No, the Seattle Fire Marshall was accomodating.

Q: What was his opinion of the Mormon Tabernacle acoustics?
A: Dr. Harris was a protege of Harvey Fletcher, who was a devout Mormon. Cyril gave Harvey's answer: "Ah yes, very unusual!" Odd acoustics, great for singing, but not so good for symphony orchestra.

Dr. Harris related how Harvey Fletcher first hired him after the war, of being in Europe afterwards, then replacing Fletcher at Columbia.

Q: What about multipurpose halls and sound reinforcement in halls?
A: He doesn't take the multipurpose jobs, although he sympathizes with those who can't afford single purpose halls. He wants to do the best job he can on a project, not a compromise.

Q: What about variable acoustic walls?
A: He did do a project once with curtains on walls, but he won't do that now. Moving things break, or the staff won't adjust them right anyway.

Q: Comments on important factors about the musician's performing stage area?
A: This is very important. The Benaroya stage is isolated, but has a wooden connection between the stage and through the audience area; you can feel the bass through the audience area.

Q: Which of your halls is the best? Have you had any flop projects?
A: No flops! He thinks Benaroya is the best hall in the world. It has everything the best European halls have, plus clarity.

Q: How does the hall measure?
A: Beautifully. And the orchestra sounds better and is playing better over the past year.

Q: What was the extent of his influence on air handling and lighting design?
A: He worked very closely on these. He'd always done air handling design himself, but for Benaroya he brought in a trusted consultant to help. There were no conflicts on the HVAC (heat, ventilation, air conditioning) design. The lighting consultant takes final responsibility on the choice of fixtures, which is mostly figuring if the lights would be quiet enough. Regarding lights, he told a story about the CBS Liederkranz Hall (in NYC) with variable acoustics. Could the musicians hear the difference when the room acoustics were changed? Yes, the staff told him - but merely changing the lightbulbs to pink affected the musician's perception, too.

Dr. Harris felt that if he doesn't like the architect and his ideas, he will refuse the project.

Q: is the RT60 reverberation measurement valid since the room is so quiet?
A: Yes, you need the same measurement to compare to other rooms, and it's the slope that is important.

Finally, door prizes were awarded - some headphone adapters, AES Journals, and an autographed coffee table book on Benaroya Hall, "Design for Music" by Ken Gouldthorpe, provided by the hall.
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Last Modified 11/4/2001