Note from your errant blogger(s): Life is currently kicking our collective asses, both professionally and (for some of us) personally, hence the eerie quiet of late at the cocktail party. So much cool stuff, so little time to blog about it! For my part, I've just finished copy-editing The Calculus Diaries manuscript, and am heading off to the San Diego Science Festival, where I will be on a panel on science and science fiction (with David Brin and Scott Sigler, no less!). But I've been blogging for enough years now, that some of you may have missed cool posts from yesteryear. So to tide you over until I get back to blogging this weekend, here's one of my favorite early posts, on concert hall acoustics, inspired by a Jordi Savall performance. And hey, if you hunger for fresher fare, I'm still blogging over at Discovery News.
Back in March, I visited my beloved New York City, having snagged tickets to see a concert performance by the incomparable Jordi Savall, world-renowned master of the viola da gamba and two-time Grammy nominee, whose soundtrack for the French film Tous Les Matins du Monde has sold more than a million copies worldwide. For this event, Savall performed with the Hesperion XXI ensemble and La Capella Reial de Catalunya, both of which he founded. Jen-Luc Piquant is as big a fan of Jordi Savall's music as I am, and we were thrilled at the opportunity not only to hear him perform live, but also by the featured pieces: early Renaissance and Baroque compositions from the Iberian Peninsula region. These are unusual, little-known compositions that Savall has taken upon himself to revive and introduce to classical audiences around the world.
A bit of history: the first Jesuit missionaries in Brazil and Paraguay adapted traditional Amerindian melodies of that region to Christian doctrinal texts translated into the local languages. They even recruited local musicians to take part in the ceremonies, clad in their native garb and playing their own culture's instruments. Inevitably, the two musical traditions merged, combining (according to the program notes) the "European model system, formal structure and contrapuntal techniques... with their own melodic and rhythmic patterns," particularly those associated with native dances. This resulted in some odd, yet affecting hybrids, such as Juan Garcia de Cespedes' Ay qye me abraso -- literally, "I am burning." It features a rhythm based on a popular Mexican dance. The secular aspect is offset by the lyrics: the characters are "panting and sighing because of the excessive heat generated by their emotions at the sight of the newborn Christ." Our own more sonorous, politely composed Christmas carols seem downright emotionally tepid in comparison.
If only the organizers of the event had paid more attention to the venue, the evening would have been an unqualified success. There's no shortage of performance spaces in Manhattan, after all, with decent enough acoustics for this type of music -- the gloriously Gothic St. John the Divine would have been ideal. Alas, the concert was held at St. Paul the Apostle on the Upper West Wide, a small Romanesque-style house of worship whose architectural details added up to a veritable acoustical "perfect storm." Unless one happened to be sitting in the first few rows, the sound was muted, muddy, and each separate part of the complex compositions seemed to reach the audience at different times, so that the percussion always seemed a few beats behind the singers, and/or the instruments.
Needless to say, the evening was an unmitigated disaster. Several audience members left in disgust, and those who remained to the bitter end were forced to wander forlornly about the sanctuary in hopes of finding one of the "live" spots where the acoustics weren't quite so ruinous. Since it was impossible to fully appreciate the performance, our little group instead found ourselves discussing the scientific aspects of what might be happening to cause the horrific effects.
Composers have always recognized the importance of the acoustics of a given performance space, and many tailored the music they composed to fit those spaces. For instance, Gregorian chants fare well in medieval cathedrals, known for long-reverberation times; ditto for organ music, such as Bach's "Toccata in D Minor." In contrast, Mozart and Haydn composed music to be played in highly furnished chambers, for smaller, intimate audiences. Such pieces lose their clarity when played in highly reverberant spaces. But no one really thought about how to design a concert hall or opera house to achieve optimal acoustics; it was done through trial and error, with little acoustical theory to provide much of a framework to centuries of experiment.
The 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.
Sabine concluded that the Fogg Lecture Hall's reverberation time was too long -- a spoken word would remain audible for 5.5 seconds, as opposed to the optimal reverberation time of 2.25 seconds -- so there was too much resonance and echo. He solved the problem by outfitting the space with sound-absorbent materials to reduce the "echo effect." His success cemented his reputation and he went on to serve as acoustical consultant for the design of Boston's Symphony Hall, still considered one of the best halls in the world in terms of sound quality. And oh, yes: the unit of sound absorption, the sabin, was named after him.
The 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. Acousticians can use those models to calculate the impulse response of the sound. Once the sound field of a modeled space has been determined, it's possible to simulate the sound as it would appear within the real space -- a technique called auralization, the acoustic equivalent of visualization techniques. Auralization software can help acoustical consultants predict, and perfect, how a proposed peprformance space design will sound, based on a wide range of parameters: room size and shape, surfaces, and materials, among other design features.
Auralization is still in its infancy when it comes to concert hall acoustics, but a team of Korean scientists has developed a way to paint "sound pictures" in space: specifically, a technique for controlling the sound in a selected region of listening space. They compare it to painting a picture on a canvas using "acoustical paintbrushes." They mix and overlap sound strokes by playing multiple loudspeakers simultaneously to create interference effects. The end result is a "photocopy" of, for example, a symphony hall's sound picture. The technique is called sound field reproduction.
Getting back to that infamous Savall concert: there were clearly many different factors at work on the night of the botched acoustics. For instance, different musical styles require different reverberation times. If reverberation time is too long, the notes blend together too much, so that it becomes difficult to distinguish individual notes in fast, complex passages. I had been especially looking forward to hearing my first villancico: a religious song performed in the vernacular, incorporating percussive African dance rhythms and a highly theatrical call-and-response effect between soloists and the chorus (tutti). All the pieces that night featured quick tempo changes, unusual rhythms and complex vocal combinations. Throw in the odd percussionist and a woman with castanets and high heels stomping her way through some of the pieces to add even more of a staccato beat, and the result was a hopeless muddle of reflected sound -- because of an overly long reverberation time.
The shape of the performance space plays a vitally important role in all of this, because it affects how sound is distributed in that space. Fan-shaped halls, favored for theaters and early cinemas, lack sufficient side reflections to achieve good sound quality (specifically, the pleasurable sensation of being "enveloped" in the music), while the circular and elliptical shapes favored by many architects tend to focus sound on certain "hot spots," leaving much of the remaining space acoustically "dead." St. Paul the Apostle's main sanctuary features a long gallery topped by a high curved roof -- I believe the technical term is a "barrel vault" -- lined on both sides by decorative archways. I'm not sure if that qualifies as a "shoe box" shape, but the poor acoustics would indicate that it is not. Making matters worse, the floor is mostly wood, with marble tile borders, so too much sound is absorbed. Add in poor line of sight, and you've got that muted, muddied quality to the music in question.
Frankly, the performance by Savall's ensemble du jour would have been better served if it had been given in the subway station. There's a reason so many buskers favor specific spots in New York City's vast subterranean transit network. Alex Case, director of Fermata Audio and Acoustics in Portsmouth, New Hampshire, has conducted extensive studies of local musicians who play regularly in subway stations. I interviewed Case -- who wears a second hat as a professor at Berklee College of Music in Boston -- back in 2004 during a meeting of the Acoustical Society of America about his NYC subway work. Basically, he recorded numerous subway "performances" with portable digital recorders and then analyzed the data he'd collected.
The walls of those stations are made of rigid heavy materials like tile, stone, steel and concrete, all of which are better at reflecting sound waves. This allows sound pressure (volume) to build up naturally, with no need for extra amplification -- that all-important reverberation. The same sound, heard up close, has much less reverberation. (This is also the same reason why so many people enjoy singing in the shower.) In fact, Case likes to mention that there's a very famous tile-and-concrete stairwell outside a professional recording studio in Manhattan that serves as an excellent "reverberation chamber" and has featured on several classic rock recordings.
Not surprisingly, he found that those stations with acoustical qualities in keeping with the established numerical criteria embraced by professional sound consultants, also proved most popular with street musicians. For instance, buskers instinctively seek out locations near hard walls and under low ceilings to amplify their music above the routine din. They also tend to avoid stations with lots of announcements, or major transfer hubs, since there are too many trains running through the station to provide enough time for an extended performance period.
Of course, the very qualities that make subway stations so good for the street musicians can also be blamed for the notorious incomprehensibility of the routine service announcements over the MTA's public address system. (Jen-Luc Piquant firmly believes the audibility of such pronouncements is inversely proportional to the importance of any given announcement.) Amplifying speech requires far less reverberation than music. What sustains musical notes by building up sound reflections causes speech to become mushy and unintelligible. The reflections all mix together so that individual words can't be deciphered. Add in the electronic amplification, and it's little wonder the announcer sounds like he/she is speaking with a mouthful of marbles.
We love subway buskers, and we love Alex Case for choosing to study the acoustics of those performances rather than (or in addition to) the more hoity-toity, elitist performance spaces -- conventional opera houses and symphony halls, for example, which are quite nice in their own right, don't get me wrong. They just exclude a large percentage of the population. Case loves the broad accessibility of the subway, pointing out that some 7 million people ride the NYC subway system every day. Even if only 1 in 10 passengers pay attention to the music, that still adds up to about 700,000 listeners per day, from every conceivable social demographic. In comparison, Carnegie Hall and Lincoln Center, combined, would have to sell out 54 shows every day, on all six main stages, just to compete. So the subway is the concert hall of the huddled masses.
Savall himself has something of Case's "common touch." The Spanish and Portuguese composers featured in the program that night combined high and "low" art, seeking to embrace the "pop culture" of their time. This might explain why there were so many young people in the audience. Classical musical aficionados are constantly bewailing the absence of youth in their audiences. Perhaps it's because the mainstream programs are so predictable: great music, yes, but always the same pieces by the same composers. This isn't an approach likely to appeal to younger, hipper audiences, who are far more likely to gravitate towards fresh alternatives, such as lost or rediscovered historical gems from, say, the 10th to the 18th centuries. That's Savall's specialty. His bio in the program notes offers his success as "proof that early music does not have to be elitist or of interest only to a minority, and that it can and indeed does appeal to an increasingly large and young audience." Savall is making classical music cool.
On the way out after the performance, I picked up a church bulletin, hoping to glean a little information about the building's history and design. Mostly it contained the usual church announcements, but on page 2 there was an item about the new sound system being installed in the sanctuary to address the chronic acoustical problems. It made mention of the need to eliminate certain "dead spots" in the sanctuary, not to mention increasing clarity in the spoken word in the nave. (The church leaders declined, however, to carpet the marble floors and stone pillars to better absorb sound to eliminate the echo effect completely, purely for aesthetic reasons.) Given the fact that Savall is such a terrific ambassador for early music, in addition to being a world-class musician, it's doubly appalling that the organizers would deliberately book his ensemble in such a well-known acoustically challenged space. Yes, it was malice aforethought. Savall et al deserved better. And so did his audience.