The structurally rigid Acoustic Composite Sheet Material from 3M, St. Paul, comes in densities from 7 to 20 lb/ft3 and thickness from 1 to 3 in. A 2-in.-thick panel has a sound-absorption coefficient of 0.09 at 125 Hz and 0.28 at 4,000 Hz (ASTM C423-90a, and E795-91, type A mounting), for example. The material can be shaped using ordinary tools and resists water, oils, solvents, acids, and bases. It's available in either 48-in.-square sheets or 16 3 48-in. aluminum-framed panels.

This sound enclosure made with 3M's Acoustic Composite Material lowers noise from a vibratory parts feeder by 33 to about 83 dB. The panels attach side by side with reclosable fasteners and tape, also from 3M. Acoustic curtains further cut noise levels and echo. A baffle or louver in the ceiling of the enclosure lets air pass through to dissipate heat while keeping sound contained.

Machine maker Com-Tal Machine & Engineering, St. Paul, recently switched to the 3M product when traditional sound enclosures made of Plexiglas, fiberglass, and foam rubber failed to consistently reduce 116-dB noise from its vibratory parts feeders to 85 dB or less. "OSHA requires personal-hearing protection for workers when noise levels exceed 85 dB for 8 hours at a time," explains Mike Rowley, a project manager for Com-Tal. "Many customers these days are writing a decibel level into a machine specification. The 3M Acoustic Composite Sheet Material helps us meet both customer expectations and OSHA guidelines."

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