Martin Hirschorn
Industrial Acoust. Co., 1160 Commerce Ave., Bronx, NY 10462
Uno Ingard
MIT, Cambridge, MA
Post-WWII jet aviation, air conditioning, quieter working and living conditions, and OSHA legislation necessitated new noise control products largely based on fibrous sound absorptive materials. In June 1994 the U.S. Department of Health and Human Services announced that fiberglass is a material ``reasonably anticipated to be a carcinogen.'' Nonfibrous silencers, noise suppressors, and sound absorbers have already been developed, for reasons unrelated to this announcement, for over 40 years---longer when automobile mufflers, Maxim silencers, and Helmholtz resonators are considered. Nonfibrous aircraft ground jet engine noise suppressors provide superior acoustic performance and durability. Nonfibrous HVAC silencers and sound absorbers are used in medical operating rooms and others requiring a risk-free environment. The design of nonfibrous silencers, rooms, sound absorbers, and encapsulated fiber designs for various acoustical requirements will be discussed. Most sound absorptive materials lend themselves well to mathematical modeling. Absorption characteristics of a variety of future absorber configurations, including their nonlinear behavior in intense sound fields, will be presented. Such designs are often perfected by means of laboratory models tests, with airflow if applicable, before finalization. For certain nonfibrous duct liners, the possibility of negative insertion loss must be considered.