ASA 127th Meeting M.I.T. 1994 June 6-10

3pNS2. Highlights of hearing protection.

Paul S. Veneklasen

Western Electro Acoust. Lab., 1711 Sixteenth St., Santa Monica, CA 90404

Before WWII Dr. Vern Knudsen began the development of ear defenders. In December 1941 this project suddenly took on great urgency; models were developed through V29. Performance was measured by threshold shift. Extreme industrial and military exposures were measured and tentative limit suggested. Development continued at Harvard Psycho-Acoustic Laboratory, resulting in V51. This device was produced in huge quantities for military and industry by MSA. At Harvard two other devices were developed: a comfortable dual-seal circum-aural headphone cushion and an insert device, called the Harveltip, derived from the V51 for coupling a miniature receiver. Both of these were in response to interference of increasing noise with military communication. At Harvard Bob Wallace conceived and tested the possibility of ``active'' noise suppression. Substantial improvement in direct person-to-person speech communication occurred with a good ear defender. After the war, research progressed with improvement over the Harvintip. The limit of achievable protection with exposed head was due to bone conduction. A method was developed for measurement of attenuation at much higher exposure. All this experience yielded clarification for necessary design parameters.