Natl. Inst. of Standards and Technol., Sound Bldg. , Rm. A147, Gaithersburg, MD 20899-0001
Small size, good frequency response characteristics, wide dynamic range, low cost, low sensitivity to external influences such as vibration, and low power requirements (extended battery life) of associated electronics have long been recognized as desirable properties of microphones used in hearing aids. New technologies of micromachined silicon capacitive microphones show promise not only for present hearing aid applications, but also for evolving array-based ones that may become practical for improving speech reception in the presence of noise and reverberation. Stability of microphone sensitivity can be particularly important in maintaining the designed directionality of arrays during their service lifetime. Designers of new microphones need reliably measured performance data to develop these new technologies and to optimize designs for specific applications. NIST measurement services long available to the public have been extended to obtain these data. Examples, including free-field sensitivity level versus frequency characteristics, are discussed for some experimental prototype omnidirectional microphones recently designed by J. Bernstein of Draper Laboratory, a customer of these services. Some possible lines of research and development of micromachined silicon transducers for hearing aid applications are suggested and discussed.