ANYONE who lives near an airport or nightclub knows the value of soundproofing. Now scientists in Hong Kong have devised a new kind of sound reflector that can cut out hard-to-block low-frequency sound.
Such a material has been elusive because sound waves are usually only reflected by structures of a similar size to the wavelength of the sound. Because low-frequency noise has wavelengths of several metres, shutting it out would normally need soundproofing the size of outdoor sculptures.
But now Ping Sheng's group at the Hong Kong University of Science and Technology has made a sound shield just a few centimetres thick. They got their inspiration from the way light bounces off metals. "We started by asking why should there be such a material for light but not for sound," explains Sheng.
They found that a 1-centimetre lead ball coated with rubber scatters sound with just the right efficiencyjust as ...
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