HALL MARKS II
The U.S. is not overly endowed with good concert halls, nor are many of them suitable for making good recordings. Our two most famous halls are Carnegie Hall in New York City and Symphony Hall in Boston. Unfortunately, because of the noise from the subways that regularly run beneath Carnegie Hall, among other reasons, very little recording takes place there. On the other hand, over more than 60 years many recordings have been made in Boston Symphony Hall.
The famed acoustics of Carnegie Hall, built a few years before Boston Symphony Hall, were a matter of happenstance. Boston Symphony Hall, opened in 1900, was the first concert hall in the world whose design relied on the use of scientific acoustic principles. Those principles were formulated by Dr. Wallace Clement Sabine of Harvard University.
In December 1987, well-known acoustician Leo L. Beranek, who has had a very close association with the Boston Symphony Orchestra, including service as Chairman of the Board, took the Boston Section of the Audio Engineering Society on a tour of Boston Symphony Hall. Dr. Beranek covered many of the historical aspects of the hall, explaining construction details and what effect they had on its acoustic properties. The November 1988 issue of the Journal of the Audio Engineering Society presented a transcript of Dr. Beranek's remarks on this tour.
This detailed account and its accompanying photographs make fascinating reading. Much of what follows is derived from that article, including direct quotes from Dr. Beranek. Without in any way denigrating his presentation, I have taken the liberty of commenting on some of his remarks, which other acousticians may find controversial in nature.
By way of background, Leo L. Beranek was one of the founders of Bolt Beranek and Newman, well-known Boston acoustical consultants. During the years he was active with BBN, Beranek regularly attended AES Conventions, where it was my pleasure to chat with him about acoustics and recording. I would gently "needle" him for the ongoing acoustic problems of New York Philharmonic Hall (which he had designed). As many know, Philharmonic Hall was stripped down to the bare walls and, with the generous gifts of Avery Fisher (for whom it was then renamed), reconstructed according to a design by eminent acoustician Cyril Harris. Avery Fisher was kind enough to invite me to inspect and observe the hall when it was under construction, so I am quite familiar with the materials and procedures which contributed to the acoustics of this hall.
Founded in 1881, the Boston Symphony Orchestra played the first 19 years of its concerts in what was known as the Music Hall, which had been modeled after the famous Gewandhaus in Leipzig (in what is now East Germany). When the City of Boston decided to tear down the Music Hall (though as it turned out, they never did), the orchestra's founder and patron, Henry Lee Higginson, resolved to build a new and larger hall.
At Harvard, where, a few years earlier, the Fogg Art Museum had been built, the museum's original building had an auditorium in the form of a cylinder. It had such bad acoustics that lectures given there were largely unintelligible. Harvard's president, Charles William Eliot, went to the Physics Department for help, and the assignment was given to an obscure assistant professor, Wallace Sabine. By dint of some original thinking in respect to room volume, absorbent materials, and reverberation time, Sabine worked out his classic equations for calculating reverberation and absorption coefficients. Sabine succeeded in making the offending auditorium useful, and a grateful Eliot recommended to Henry Higginson that Sabine be commissioned to undertake the acoustic design of the new concert hall.
Higginson had earlier hired the architects McKim. Mead and White. After a year's effort, they came up with a design that looked like a Greek amphitheater with a stage and a roof. Higginson took the design to Europe, where he consulted various conductors and musicians. They had never seen anything like it and unanimously condemned the concept.
Sabine had accepted the commission for the acoustic design of the proposed hall and learned that Higginson, after returning from Europe, told the architects to copy the Gewandhaus in Leipzig. The Gewandhaus had only one balcony and seated 1,560. In order to meet the 2,600-seat capacity proposed for the new hall, architect Charles McKim merely increased all the dimensions of the Gewandhaus by a factor of 1.3.
Fortunately, Sabine had his formulas and equations for reverberation time, and he had measured the absorption coefficients for upholstered seats and for an audience. He used this knowledge to calculate the reverberation time for the Gewandhaus and for Mc Kim's expanded version of it. Sabine determined that the reverberation time for McKim's proposed hall would be over 3 seconds. Because the new hall was intended to be much wider, the resulting sound would be very cavernous, like a gymnasium's. Therefore, he told McKim and Higginson that they shouldn't proceed with their plans. Sabine pointed out that the old Music Hall was built on the same concept as the Gewandhaus. In his AES tour lecture, Beranek quotes Sabine as saying, " 'It is rectangular, has many irregularities on its walls and ceiling, and people like its sound. Let us simply copy it and lengthen it a little by adding a stage house.' " The old Music Hall had balconies extending over the sides of the stage, so members of the audience could actually look down on the musicians. Because Sabine didn't think that this was a very good idea, he suggested eliminating the end wall of the Music Hall. In his view, adding the stage house would give the new hall the extra capacity to accommodate 2,600 people and would eliminate the overhanging balconies. Higginson and the architects agreed, and that is how Boston Symphony Hall was built.
Sabine and the architects incorporated several features which greatly contribute to Symphony Hall's good acoustics. For example, built-in along the walls are niches which contain classical statuary. This provides good diffusion of the sound in the hall. Sabine had the fronts of the balconies perforated, which provides diffusion and avoids echoes. The ceiling is coffered, with about a half-dozen different sizes and shapes of coffers affording even more diffusion of the sound. Sabine was farsighted enough to provide "quiet" ventilation. By 1887, electric motors and large fans were available.
Sabine recommended that one-fifth of the ceiling be perforated to allow fresh air to drop down into the hall. The exhaust air goes out through grilles on the lower side walls. Sabine's design also included corridors and offices surrounding the hall. These act as "air buffers" to isolate the hall from street noises. In the early days, horse-drawn wagons on the cobblestone-paved streets made a lot of noise, but the corridors still do a good job of noise suppression. However, sometimes noises do creep in during recording sessions. During a quiet passage of an RCA Red Seal recording of "Scheherazade" (I believe Erich Leinsdorf was conducting), you can hear a bus accelerating outside!
Boston Symphony Hall opened in October of 1900. It didn't receive very good reviews, but this was mainly due to complaints by visiting European orchestras and conductors. In those days, the orchestras had about 90 players, and the Europeans were used to performing in smaller concert halls which seated 1,400 to 1,600 people. In the larger volume of Boston Symphony Hall, with its 2,600 seats, they felt that their music didn't sound loud enough and that it was weak and thin. In his wonderful book, Music Acoustics and Architecture, Dr. Beranek points out that the median size of most halls in England, Canada, the U.S., South America, and Israel is about 3,000 seats. The present-day orchestral strength of 107 to 110 players provides much louder sound, although Beranek says that in Boston Symphony Hall, an orchestra of 120 players would be needed to approximate the loudness levels of the 90-piece orchestras in the small European halls.
Boston Symphony Hall has a foundation of poured concrete, and its walls are constructed of hard plaster over concrete blocks. The upper part of the hall is the same except that the concrete blocks are hollow. There are no rugs, except in the aisles, and they are quite thin. There is also no wood except around the stage. The architects designed the stage's side walls to make a pleasing appearance. These walls are of 1-inch-thick wood with many irregularities, which provides good diffusion and good sound. Sabine designed the stage enclosure partly to accommodate the pipe organ, making sure the bottoms of the pipes were over the musicians' heads.
Dr. Beranek has strong feelings about the use of wood in a concert hall. Although most musicians believe strongly that the best sounding concert halls have interiors entirely made of wood, Beranek counters by saying that few of the best halls in the world are actually made of wood. In his opinion, wood tends to weaken and attenuate bass response. Dr. Beranek says hard interiors with plenty of diffusion will provide the most favorable mixing of sounds and a good feeling from the reverberation.
Now, it is important to understand that acousticians today are not bashful about criticizing each other's designs. For example, a number of acousticians feel that rectangular halls--like the Gewandhaus, Boston Symphony Hall, Orchestra Hall in Minneapolis, and now Avery Fisher Hall-are all "wrong" and derisively label them "shoe boxes." They espouse the wider, fan shaped halls. (It must be noted that most fan-shaped or "wedge" halls are multi-purpose halls, while rectangular halls are used mainly for classical concerts.) Dr. Beranek's feelings about wood are strongly challenged by Cyril Harris' design for Avery Fisher Hall, in which the stage enclosure is wood and the walls of the hall are of heavy, overlapping. 1-inch-thick, random-size wood panels. Harris is also a strong believer in the value of diffusion, as evidenced by his controversial use of "cuboid" reflectors behind the stage (and partially on the ceiling over the stage) in his design of Orchestra Hall in Minneapolis. A slight "slap echo" at about 100 Hz has been attributed to these reflectors.
According to Dr. Beranek, a stage floor should be made of wood but need only be strong enough to support the orchestra--"it doesn't need to support a truck." With the kind of floor construction in Boston Symphony Hall, he states that the energy transmitted by the pins of the cellos and contrabasses to the floor cause it to resonate and provide a richer sound. In contrast, the stage floor in Avery Fisher Hall is made of heavy oak planking, laid edge-wise. It has great strength but is less resonant. General opinion seems to be that bass sound in Avery Fisher Hall is not as full but is extremely clean.
Sometimes, instruments rest not on the stage floor but on risers, which elevate certain sections of the orchestra, usually the brass and some woodwinds, above the strings. Dr. Beranek noted that conductor Charles Munch didn't use them, while the first thing Erich Leinsdorf wanted was the risers replaced. Stokowski believed in them and taught me to use them. I used risers when I recorded Arthur Fiedler and the Boston Pops in Symphony Hall. String players tell me they feel better and have better concentration when trumpets and trombones are not "blowing off the back of their heads." However, risers should be sturdy, and neither percussion nor string bass should be on risers, which would resonate too much and muddy the sound.
The reverberation period of Symphony Hall is about 1.8 seconds at mid frequencies, rising to about 2.1 seconds at lower frequencies when all 2,600 seats are occupied. When the hall is empty (as it obviously is during recording), the reverberation time rises to 2.7 seconds at the lower frequencies, which can be quite a problem in recording. Over the years, various measures have been undertaken to compensate for this longer reverberation time. RCA engineer Lew Layton built a 25-foot "lip," or extension, to the stage to bring the orchestra further out into the hall; I used this extension when I recorded Arthur Fiedler. Since Jack Renner of Telarc (who recorded the Beethoven Piano Concertos with Rudolf Serkin) and I both used spaced array omnidirectional mikes in Symphony Hall, we had to be extremely careful in balancing our ratio of direct-to-reflected sound pickup. Some European record companies used 25 to 35 microphones in a very close-up manner in order to "swamp" the hall acoustics; later on, they ran the tapes through a spring-reverb unit to provide ambience. (Nowadays, they use digital reverb units.) If I were going to record now in Boston Symphony Hall, I would insist on seating some 2,600 pieces of polyurethane foam "instant people" to give me the same lovely 1.8 seconds of reverberation as when the hall has a live audience. John Newton, an engineer friend of mine who does a lot of work for Philips, made a wonderful recording of the Mahler Second Symphony with the Boston Symphony, and he used extensive amounts of absorbent material to dampen the hall. The result is a highly detailed recording enrobed in a lovely, warm ambience.
Boston Symphony Hall is indeed an acoustic marvel. Considering that it is a modified copy of the Gewandhaus in Leipzig, have there been any other copies made? The answer is that the concert hall at Kennedy Center in Washington, D.C. is pretty much of a direct clone, as is the concert hall in Salt Lake City, Utah. Perhaps we'll do a story on them one day.
(adapted from Audio magazine, Jun. 1989; Bert Whyte)
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