NIST, Sound Bldg. 233, Rm. A147, Gaithersburg, MD 20899-0001
Electromagnetic compatibility (EMC) issues involving acoustical instruments, especially their susceptibility and immunity to electromagnetic interference (EMI), are increasing in importance. This increase is driving domestic and international standards development. Of particular significance is the impact on commercial practice and international trade of two Councils of the European Communities directives regarding generic apparatus (Council Directive 89/336/EEC, 3 May 1989) and medical devices (Council Directive 93/42/EEC, 14 June 1993). Directive 93/42/EEC is being interpreted to include hearing aids and audiometric instruments. Numerous voluntary International Electrotechnical Commission (IEC) electroacoustical performance standards are available for some of these instruments. However, extension of these complicated standards to include all pertinent EMC issues is difficult. Development of standards for other instruments, such as those for measuring auditory brain-stem response, would be even more difficult. In some circumstances, the use of shielded rooms to attenuate radiated EMI is practical and cost-effective. In the U.S.A., at least, existing standards for measuring such shielded-room performance were not specifically developed for audiometric booths. Methods in some of these standards have been adapted and applied to that purpose. Selected standards, methods, and some considerations regarding their application to measuring the shielding performance of audiometric booths in hospital/clinical environments are discussed.