Sounds of the Subway

New York City is famous for the broad diversity of its cultural venues, particularly world class performance halls like Carnegie Hall and Lincoln Center. But the city's most popular performance space can be found in its vast underground network of subway stations.

"Ask any New Yorker and you'll get an earful of recommendations on the best stations, the best players, and how much to tip," says Alex Case, director of Fermata Audio + Acoustics, Portsmouth, NH, and a professor at Berklee College of Music in Boston.

Case himself is something of a connoisseur when it comes to subway acoustics. He's done extensive studies of local musicians who regularly play in subway stations, using portable digital recorders to capture these on-the-fly performances.

Not all subway stations are created equal. Subway buskers choose their locations carefully, avoiding stations with a steady stream of announcements, or major hubs with more than one line running through them. Delays might be irritating for commuters, but for the performers they are godsends, giving them an extended performance period in between trains. And Case has found that the buskers instinctively seek out locations near hard walls and under low ceilings, so their music is amplified above the din of the station.

Case doesn't find this at all surprising. Subway walls are typically made of rigid heavy materials like tile, stone, steel, and concrete. These materials are better at reflecting sound waves, allowing sound levels to build up naturally, with no need for microphones or loudspeakers.

As a result, subway listeners are immersed in a bath of echoed sound known as reverberation.The same sound, heard up close, has much less reverberation. Reverberation is the critical element in the design of all performance spaces, whether mainstream opera houses or alternative spaces like the subway. It's the same reason why so many people enjoy singing in the shower. "It just so happens that the sort of space that is durable, easy to clean, and graffiti resistant also happens to be sound reflective," says Case. "The musicians wallow in it. The passengers variously savor, ignore or avoid it."

So if subway stations are such terrific acoustical environments, how come it's so hard to understand the announcements over the public address system? Case says that's because amplifying speech requires far less reverberation than music. The same phenomenon that 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 the reverberation is so strong that the announcer might as well be speaking with a mouthful of marbles.

That's why acousticians like Case tailor their designs to the specific needs of performance spaces. Large opera houses like Boston Symphony Hall or Carnegie Hall have different acoustical needs than, say, Broadway theaters. For the latter, says Case, he designs spaces with more sound absorption, lowering the amount of sustaining reverberation the space adds to a speaking voice. "This makes it easier for listeners to follow the spoken word, syllable by syllable," he says.

Concert hall design isn't just about the strategic conservation of sound energy inside the performance space. A great deal of effort is also spent on suppressing the noise and vibration of the surrounding city, not to mention noise from modern amenities—the heating and air conditioning equipment, elevators and plumbing—all of which can seriously detract from the pleasure of a performance. No one wants to hear a subway rumbling or a toilet flushing in the middle of Wagner's "Ring" cycle.

For Case, the most appealing feature of alternative performance spaces like the subway is their broad accessibility, compared with conventional opera houses, which tend to be somewhat elitist. He estimates that some 7 million passengers ride the New York subway system every day. Even if only 1 in 10 passengers pay attention to the music, it still adds up to about 700,000 listeners per day, from every conceivable social demographic. Carnegie Hall and Lincoln Center would have to sell out 54 shows every day, on all six main stages, just to compete. The subway is the opera house of the people.