The Science of Silence

Winter brings the noise of clanking heaters, and other racket and yawp. But a class of experimental materials may lower the decibel level.

Winter brings the noise of cooped-up kids, clanking heaters, and other racket and yawp. But Robert Fricke of the consulting firm Arthur D. Little is trying to lower the decibel level with Lodengraf (Low Density Granular Fill), a class of experimental materials that use granular mixes, such as volcanic glass and nylon flock, to dampen noise.

According to Fricke, noise comes in two varieties: airborne and structure-borne, which is caused by vibration. It's the latter that Lodengraf is designed to lessen. Materials like sand and lead shot have traditionally been used to reduce structure-borne noise, but the sheer weight of these substances precluded their widespread use.

"It was thought that the mass of the material reduces the sound level," explains Fricke. "That's only partly true." The speed at which sound travels through the materials has a greater effect on how much you hear. Lodengraf lowers that speed. As sound radiates from a vibrating structure, it causes the particles within Lodengraf to rub together, translating the energy of sound into friction, which is dispelled as heat. In tests, Lodengraf cut the noise from an air conditioner by 70 percent.

"It works in spades," says Fricke. And he predicts that Lodengraf will one day reduce noise in everything from lawnmowers to aircraft.