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Help is at hand for noisy orchestra pits

February 20, 2002

"BEING punched in the back of the neck with a blunt instrument." That`s how William Morton, a retired flautist with the Royal Opera House orchestra in London, describes the blast of sound that assaults the senses of musicians performing in the confined spaces of an orchestra pit.

        Musicians in these claustrophobic dug-outs can struggle to hear themselves play, particularly if they`re seated in front of the brass or percussion sections. This can cause a snowball effect as performers compete. "You start playing louder to hear yourself and it quickly becomes a cacophony in the pit," says Morton.

        This not only affects the quality of the performance but is dangerous for the musicians, says Helmut Fuchs at the Fraunhofer Institute for Building Physics in Stuttgart, who has measured maximum noise levels of more than 123 decibels in orchestra pits. "Even the average is far too high at around 90 decibels," he says. "There are no other places in the world with acoustic levels like that . . . steel workers and pilots would have to wear ear protection under such conditions." This isn`t, of course, an option for orchestral musicians, who need to hear both themselves and each other.

        Now help is at hand from a new type of acoustic absorber developed by Fuchs and his colleagues. Orchestra pits are designed to project the "sound image" into the concert hall, rather than to the musicians themselves. But the cramped quarters and close proximity of fellow players can cause near-deafening reverberation as sound bounces off the nearby walls.

        While acoustic panels capable of absorbing sound are available, the only ones that could absorb the ear-blasting low frequencies that do most damage tend to be at least a metre thick, says Fuchs. And that`s not exactly practical in an orchestra pit.

        The solution the Fraunhofer team has come up with is a new breed of acoustic absorber that can handle a broad range of frequencies as low as 40 hertz, but with only a tenth of the thickness of traditional absorbers.
        Called an acoustic fibreless absorber, it essentially consists of a slim sheet of plastic foam with a thin plate of steel on top. The panel absorbs sound in two ways. The foam acts like a compressive spring absorbing frequencies as the plate pushes against it, while the steel plate does the same by flexing. "It will extract airborne acoustic energy and transform it into heat by vibrating," says Fuchs.

        He`s found the panel works best when there are as few fixture points as possible between the steel and the foam. This allows more resonances to develop and makes the panel work over the broadest range of frequencies. "This is very important and makes all the difference," explains Fuchs.
        His panels have now been installed at the Landestheater in Flensburg and the Staats- theater in Stuttgart, and have been warmly welcomed by musicians and conductors alike. "They can now play as they like. With these acoustic panels no one is forced to play louder than the conductor wants them to play," he says.

Author: Duncan Graham-Rowe
More at: Applied Acoustics (vol 63, p 203)

http://www.newscientist.com">New Scientist issue 23rd February 2002


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