ART
+ Physics = Beautiful Music
By
JAMES GLANZ
Can the sense of acoustic intimacy created by a
fine concert hall be measured in how many milliseconds it takes sound waves to
ricochet from the walls and balconies and reach a listener in the seats? Can a hall's
aural warmth be calculated from how efficiently bass notes rebound from the
same surfaces? Can the prized quality called resonance be estimated from the
rate at which the entire hall fades to silence after a blast of electronic
sound?
More to the point,
can an architect rely on studies of these quantities, using computer
calculations and measurements in scale models, to ensure that a structurally
innovative, visually inspiring design for a new concert hall will be an
acoustical triumph rather than a disaster?
For years, the
answer to all these questions seemed to be no -- the field of concert hall
acoustics has had only spotty success.
But now an
unusually intense collaboration between architects and acousticians has put the
science of acoustics to the test, with two major new successes in Tokyo.
The halls in
question are the 1,632-seat concert hall of the multipurpose complex called
Tokyo Opera City, and the 1,810-seat opera house of the adjacent New National
Theater.
Both have
architecturally daring designs, yet both have been praised by musicians who
have performed in them.
"This hall
simply has some of the best acoustics in which I have ever had the privilege to
play," the cellist Yo-Yo Ma wrote in a commentary on the concert hall that
appeared recently in a technical journal. He said its visual and acoustic
aspects combined in a rare synthesis -- "a miracle," he called it.
Miracle or no,
this is no small feat. "Going to the Moon is much simpler as a physics
problem," said William J. Cavanaugh, an acoustician at Cavanaugh Tocci
Associates who consults on both the construction and restoration of concert
halls. In a Moon shot, he said, "you've got one source, you've got one
trajectory that will get you there, and you've got one 'listener,' or destination."
But in a
concert hall, the trajectories of the sound waves begin at any number of places
on the stage, bounce in complicated ways from every cornice and pillar, and
reach their ultimate destinations in hundreds of occupied seats.
The research
for the new halls, whose principal architect was Takahiko Yanagisawa, president
of TAK Architects in Tokyo, may be the most extensive use yet of acoustical
measurements and calculations in efforts to design concert halls that are not
simply copies of great halls of the past.
"If you
make a copy of the old, great halls, you'll have a great hall," said Dr.
Leo L. Beranek, an architectural acoustician in Cambridge, Mass., who was the
principal acoustical consultant for the projects in Tokyo. But the Tokyo
concert halls, he said, "are different in appearance and they have the
sound of great halls."
The research is
described in three papers, published earlier this year in The Journal of the
Acoustical Society of America, by Dr. Beranek and Dr. Takayuki Hidaka, chief
researcher of the Takenaka R & D Institute, which conducted acoustical
measurements and built models. The papers describe how, as the designs took
shape, scientists analyzed and worked to maintain acoustical variables like
reverberation time, spaciousness and intimacy, each with a precise mathematical
definition and musical meaning.
Without those
studies, "you're gambling" on the acoustics, Dr. Beranek said.
Still, the
success of two halls in Tokyo is unlikely to persuade all critics that the
science of concert hall acoustics has finally arrived. There are still many
acousticians who maintain that a knowledge of the technical issues, while
helpful, is less important than experience and a repertoire of acoustically
successful designs that one can fall back on in a pinch.
"If you
know your craft and you know your art," said Russell Johnson of Artec
Consultants, "the math today may not help you very much. And if you
believe some math that's wrong, you can get into trouble very quickly."
That cautionary
note was echoed by Dr. Cyril M. Harris, a professor emeritus of architecture
and electrical engineering at Columbia University. The purely technical
approach "works much of the time, but sometimes it doesn't, and you don't
know the reason why," he said. "So you get trapped. And you get real
disasters."
Yet both Dr.
Harris and Mr. Johnson acknowledged that recent advances in acoustics could
yield crucial clues to designers.
The history of
concert hall acoustics is nothing if not contentious. No single approach,
whether based on science, experience, art or pure intuition, has been without
its heralded successes and unexplained failures.
In a way, in
fact, musical styles and performance venues have engaged in what a biologist
might call co-evolution, developing in ways that were inextricably dependent on
each other.
It is no
coincidence that the unhurried, vowel-rich Gregorian chants sound best in
medieval cathedrals, whose "reverberation time" -- the time it takes
a burst of sound to fade away -- is 5 to 10 seconds. Later in musical history,
the polyphonic, highly articulated Baroque compositions of Bach, Handel and
Vivaldi benefited from being played in relatively small rooms with hard,
reflecting walls, in which the reverberation times might be less than 1.5
seconds.
Those close
walls also added a sense of acoustical intimacy. That is, the delay between the
arrival of sound directly from the instruments or voices, and sound reflected
off the walls and other surfaces is slight. The smaller the delay, the greater
the sense of intimacy.
Later still, as
the Classical style of Haydn and Mozart gave way to the Romantics, large
concert halls with correspondingly longer reverberation times were built to
accommodate both the music and its growing audience.
Beethoven's
later symphonies were composed "almost as though he anticipated the large,
reverberant halls that would be built in the next half-century," Dr.
Beranek wrote in his book "Concert and Opera Halls: How They Sound"
(Acoustical Society of America, 1996).
In another
biological analogue, poor concert halls often did not survive the wrecker's
ball. In a kind of natural selection, the best halls of the 19th century were
more likely to survive. The three halls most often cited as models of sonorous
pleasure are the Grosser Musikvereinssaal in Vienna (built in 1870); the
Concertgebouw in Amsterdam (1888), and Symphony Hall in Boston (1900).
Each of those
halls is roughly shoebox shaped, leading to quick reflections from the fairly
close side walls and balconies. Each has a reverberation time of about two
seconds. And each displays numerous irregularities, like coffered ceilings and
rows of buxom statues on its interior walls. The diffusion of sound created by
reflections from those objects, acousticians agree, prevents a nasty acoustic
"hardness" or "glare" that smooth surfaces can generate.
(This diffusion is one characteristic that still awaits a precise mathematical
definition, being determined for now by visual inspection of the interior.)
Symphony Hall
rates a special status in the field, since the person generally regarded as the
first to apply science to architectural acoustics, the Harvard physicist
Wallace Clement Sabine, consulted in its design. Sabine had just discovered a
crucial formula that relates a hall's reverberation time to a hall's volume and
the amount of sound-absorbing material, like people and curtains, inside it.
"He
really, literally, put the first numbers to this whole question," Mr.
Cavanaugh said. But reverberation time alone could not divide the good halls from
the bad ones. "Anybody that was working on it knew there was a lot more to
it than one number." Dr. J. Christopher Jaffe of the Norwalk, Conn., firm
Jaffe Holden Scarbrough Acoustics, who also directs a program on sonics in
architecture at Rensselaer Polytechnic Institute in Troy, N.Y., said that a
more complete translation of the warm, rich sound of the great 19th-century
halls into scientific terms owed much to the development of fresh acoustical
measures, or "metrics," by Dr. Beranek.
"Leo got
the Rosetta Stone to get that traditional sound developed into reflecting
patterns," Dr. Jaffe said. "That gave the architects some great
freedom."
That freedom,
he said, is most useful for designs, like those of the new halls in Tokyo, that
do not carefully copy the tried-and-true, shoebox-shaped halls.
Like intimacy
and reverberation time, the additional metrics have deceptively simple names
like spaciousness, bass ratio, acoustical texture and clarity. But each has a
precise mathematical meaning that seeks to isolate a specific aspect of
acoustical quality in a hall. In the studies leading up to the design of the
new Tokyo halls, said Dr. Hidaka of the Takenaka R & D Institute,
measurements of those and other metrics were made in 20 opera houses and 25 symphony
halls in 14 different countries. (While New York's Carnegie Hall is considered
among the world's best, it was not included in the study because there was no
opportunity to make acoustic measurements there, Dr. Beranek said.)
The idea, Dr.
Hidaka said, was to get a quantitative measure of what made the good halls good
and the bad ones bad. For the studies, his team generally produced a burst of
sound from a 12-sided speaker on the stage -- actually a dodecahedron with a
small speaker on each face. Each burst and its acoustic aftermath was recorded
on tiny microphones placed in the ears of dummies, and in some cases the ears
of real people, scattered around the seats.
The team worked
out the value of the various metrics for each hall by analyzing detailed forms
of the sound waves picked up by the microphones. Intimacy, for example, was
defined as the time delay between the direct arrival of the sound from the
stage and that of the very first reflections, which have presumably bounced off
protruding side balconies.
Bass ratio
gauges how efficiently low notes, compared with middle notes, carom from the
walls and other surfaces; a high bass ratio gives a hall what musicians call
warmth. Spaciousness is an estimate of what fraction of all the sound bathing a
listener has been reflected laterally, from interior surfaces, as opposed to
having arrived straight from the stage.
Dr. Beranek,
Dr. Hidaka and their collaborators then compared those measurements with an
acoustic ranking of the halls based on a survey of conductors and music
critics. They found that the most beloved concert halls had reverberation times
near two seconds, intimacy times of not much more than 20 milliseconds and
relatively high bass ratios and spaciousness factors. Other metrics also took
on fairly consistent values in the best halls.
Because of the
need for greater clarity in understanding voices, the optimum reverberation
times for opera houses turned out to be shorter, around 1.5 seconds.
Then the
acousticians turned to large computers that had been programmed to simulate the
acoustics in the basic architectural designs of Mr. Yanagisawa.
The team
eventually built a 10-to-1 scale model of the proposed designs and made just
the same measurements, using tiny speakers, microphones, and one-inch "heads"
of dummy audience members, all scaled down in proportion to the model.
Even the
wavelengths of the sound in the model measurements were scaled down.
This work led
to numerous adjustments in the original designs, including changes in the
height of the ceiling near the stage in the concert hall, giving some of the
balcony fronts a rakish, forward slant and adding a special sound-diffusing
material to the pyramidal ceiling.
The reflected
wave patterns in the finished Tokyo Opera City concert hall, wrote the team in
one of its papers, "appear to be closest to those for Boston Symphony
Hall." Dr. Hidaka said acoustic data for the opera house resembled those
of the famed Vienna Staatsoper.
For all the
apparent success of the Tokyo projects, Mr. Yanagisawa emphasized that
acoustical studies were far from the whole story. He believes that his general
immersion in the music of the great halls of the world played as large a role
in his understanding of good acoustics as the results of the technical work
did.
"I believe an
excellent hall can only be realized by a design that assimilates nuances beyond
description by scientific data," Mr. Yanagisawa said. "The final work
is a world of sense created therefrom."
VINDICATION
As a chapter in
the fractious history of architectural acoustics, the success of the new Tokyo
concert halls can be seen as a vindication for Dr. Leo L. Beranek, who received
years of negative publicity after the 1962 opening of New York's Philharmonic
Hall, for which he was principal architectural consultant. The bad reviews
garnered by the hall's acoustics cast a shadow over the scientific approach to
acoustics that he was then developing.
But in the long
run, the message from that failure has been decidedly mixed. The science was
far less developed in those days, and the architects did not follow many of Dr.
Beranek's suggestions, partly out of financial concerns.
Even after Dr.
Cyril M. Harris, now a professor emeritus of architecture and electrical
engineering at Columbia University, led a complete reconstruction in the 1970's
-- when it became Avery Fisher Hall -- and Russell Johnson, an acoustician at
Artec Consultants, made further adjustments to the stage in the 1990's, a kind
assessment would say that the hall is still not considered among the world's
best acoustically.
"At that point,
in a sense, the architects had much more say about things," said Dr. J.
Christopher Jaffe, an acoustician. There used to be a feeling, he said, that in
acoustics, everybody thinks differently, so none of the recommendations need to
be taken seriously. But that attitude has changed, Dr. Jaffe said.
