Soede W, Berkhout A J, Bilsen F A
Delft University of Technology, Faculty of Applied Physics, The Netherlands.
J Acoust Soc Am. 1993 Aug;94(2 Pt 1):785-98. doi: 10.1121/1.408180.
A directional hearing aid might be beneficial in reducing background noise in relation to the desired speech signal. Conventional hearing aids with a directional cardioid microphone are insufficient because of the low directivity of cardioids. Research was done to develop microphone(s) with strong directional characteristics using array techniques. Particular emphasis was given to optimization and stability. Free-field simulations of several robust models show that a directivity index of 9 dB can be obtained at the higher frequencies. Simulations were verified with a laboratory model. The results of the measurements show a good agreement with the simulations. Based on simulations and measurements, two portable models were developed and tested with a KEMAR manikin. The KEMAR measurements show that the two models give an improvement of the signal-to-noise ratio of approximately 7.5 dB in a diffuse sound field. It may be concluded that the developed microphones have the capability to reach a significant improvement of speech intelligibility in noise under practical circumstances.
