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The tricky art of acoustic engineering

The wall of sound

Acoustics can make the difference between a good building and a bad one. Simon Willis meets the architects and engineers finding new ways to control the cacophony

Acoustics can make the difference between a good building and a bad one. Simon Willis meets the architects and engineers finding new ways to control the cacophony

Simon Willis | April/May 2018

The new National Music Centre in Calgary, Canada, is covered inside and out with metallic tiles, giving it the glint and gleam of an old trombone. Its affinity with a musical instrument is not just a surface effect. The centre houses two concert venues, a radio station, the Canadian Music Hall of Fame and galleries exhibiting 450 years of musical memorabilia, including the mobile studio in which the Rolling Stones recorded “Sticky Fingers” and “Exile on Main St”. Its architect, Brad Cloepfil, wanted to make each space distinct, so he arranged them across a series of nine towers. But the building also needed a sense of cohesion, and for that he used sound, turning the entire structure into the architectural equivalent of a mixing desk.

With the help of Jaffe Holden, one of the world’s leading acoustic consultancies, he developed complex digital models of how sound would behave inside. On the one hand he wanted music to drift through the building, holding its parts together like sonic glue. He left the main concert hall open to the lobby and connected the towers via a series of curvaceous atriums, bridges, stairways and soaring “acoustic canyons” (pictured). But he also needed to control its journey. Once the sound reached the upper galleries, for example, where visitors would be wandering through exhibitions, it had to be a gentle hum rather than a distracting cacophony.

According to Jaffe Holden’s models, bass would puddle in the central galleries, causing an annoying throb, while high frequencies would reach the side galleries like the tinny noise from someone else’s earbuds. To counteract this, they suggested minute adjustments to the distribution of tiles in places where sound would land, and inlaid the gaps with absorbent material to control where, and in what quantity, it went next. The result was a building that edits noise as it goes. The musicians who perform here aren’t just playing their guitars or violins, Cloepfil says, “they’re playing the whole building.”

The National Music Centre shows just how far the science of architectural acoustics has come. It was invented in 1895 by a young Harvard physicist called Wallace Sabine, who was asked to fix the acoustics in the lecture theatre at Harvard’s Fogg Art Museum. It had opened that year in a Beaux Arts building designed by Richard Morris Hunt, whose other work included the façade of the Metropolitan Museum of Art in New York and the pedestal of the Statue of Liberty. The theatre, complete with marble columns and a domed roof, offered a magnificent stage for America’s most eminent art historians. Except that as soon as they started talking, their words became an unintelligible mess of echoes bouncing around the hard stone surfaces of the cavernous interior. The acoustics were so bad that the new hall was unusable.

Armed with a pipe-organ, a stopwatch and a team of keen-eared assistants, Sabine began an intensive study. First he measured how long it took for a sound to become inaudible in the room – its “reverberation time” – and discovered that it was over five seconds. No wonder audiences had been assailed by a sonic pile-up: every sentence uttered by a speaker would be accompanied by the one before it. Then he set about testing materials to see how well they absorbed sound. He measured the effects of oriental rugs and varieties of upholstery. He measured human bodies, and discovered that one person absorbed about as much sound as six cushions.

The result of Sabine’s work was an aesthetic compromise: the hall’s ceiling and walls were clad in felt and asbestos cloth. But it also delivered a new physical equation, relating a room’s reverberation to its volume and absorbency. While architects had built beautifully resonant spaces before – the amphitheatre at Ephesus, say, or the Musikverein in Vienna – there had never been a way to quantify their acoustic performance. Now there was.

The main application of this science has been in concert venues (Sabine advised on the construction of the Boston Symphony Hall in 1900, still regarded as having some of the best acoustics in the world). But in recent years, there has been a boom in innovative acoustic design in other areas of architecture too, from offices and restaurants to homes and museums. Contemporary architects are fond of everything acoustic engineers despise. Like Cloepfil, they build in glass and steel, stone and bare wood, and they like large, flowing spaces instead of small, enclosed ones. This makes for light-filled, airy buildings, but it can also make for unbearable noise. In 2016 Momofuku Nishi, an Asian-Italian fusion restaurant, opened in New York in a space decked out in bare wood. Many critics enjoyed the food – one called the spicy squid chitarra “a contender for cephalopod pasta of the year” – but they loathed the acoustics, which were variously described as “abusive”, “throttling” and like “a shiatsu massage that never stops”. Not long after, it closed for a refurbishment.

The challenge is to dampen sound without ruining style. At the Battery, a private members’ club and restaurant in San Francisco, they have found a technological solution. The club is housed in an early-20th-century industrial building which, in its previous incarnations, had been home to a candy manufacturer and a crating company. When it was bought by Michael and Xochi Birch, who sold their social network, Bebo, to AOL for $850m in 2008, they wanted to strip the building back to its stonework and wooden beams to display its old industrial character. But all those hard surfaces created an acoustic problem. “The easy solution is to just engineer it with acoustic materials,” says Michael Birch, “but we’re trying to expose all the beauty of the building, and we don’t want all those ugly panels covering the walls or hanging from the ceiling for no good reason.”

They called in John Meyer, who, with his long beard and magical touch with sound, is the Gandalf of acoustic engineering. Meyer has provided sound systems to many of the world’s leading concert venues, including the Walt Disney Concert Hall in Los Angeles. He also designs them for restaurants. At the Battery, he installed a set of 16 microphones hanging discreetly from the restaurant ceiling, 17 loudspeakers and 11 deep-bass speakers. The microphones pick up noise from each table and feed it into a powerful computer, which then monitors the sound second by second and balances it for each table by removing unwanted frequencies. This edited sound is then piped back out through the speakers, acting a little like white noise from noise-cancelling headphones does, creating acoustic micro-climates around each group of diners, cutting out distracting noise while preserving a warm hubbub. “On the one hand it creates energy and buzz,” says Birch, “and on the other it provides a sense of privacy.”

Hear here

The bar and restaurant at the Battery in San Francisco, where microphones hang from the ceiling

For those whose budgets don’t stretch to complex computer modelling and state-of-the-art electronics, there are also state-of-the-art materials. Kvadrat, a Danish textile firm, has just released a range of acoustic curtains that rival felt for sound absorbency – except they are transparent. “If you have a glass façade, you want to have the sunlight, the view,” says Johanna Apelgren, a textile engineer at Kvadrat. “You don’t want to put up heavy velvets, like in a cinema.” So they developed a fabric made from threads of tape yarn – plastic filaments like miniature sellotape – woven vertically with strands of heavier fibres. The transparent tape yarn stops sound while the other threads absorb it.

Back at the Battery, Michael Birch still has one problem room – a penthouse which “is still louder than I’d like”. The culprit is the wall of glass, which offers an expansive view of San Francisco but bounces noise back into the room. “The only thing you can do with glass is add curtains,” he says. Maybe he should call someone in Denmark.