To evaluate the improvement in speech intelligibility in noise obtained with an assistive real-time fixed endfire array of bidirectional microphones in comparison with an omnidirectional hearing aid microphone in a realistic environment.
The microphone array was evaluated physically in anechoic and reverberant conditions. Perceptual tests of speech intelligibility in noise were carried out in a reverberant room, with two types of noise and six different noise scenarios with single and multiple noise sources. Ten normal-hearing subjects and 10 hearing aid users participated. The speech reception threshold for sentences was measured in each test setting for the omnidirectional microphone of the hearing aid and for the hearing aid in combination with the array with one and three active microphones. In addition, the extra improvement of five active array microphones, relative to three, was determined in another group of 10 normal-hearing listeners.
Improvements in speech intelligibility in noise obtained with the array relative to an omnidirectional microphone depend on noise scenario and subject group. Improvements up to 12 dB for normal-hearing and 9 dB for hearing-impaired listeners were obtained with three active array microphones relative to an omnidirectional microphone for one noise source at 90°. For three uncorrelated noise sources at 90°, 180°, and 270°, improvements of approximately 9 dB and 6 dB were obtained for normal-hearing and hearing-impaired listeners, respectively. Even with a single noise source at 45°, benefits of 4 dB were achieved in both subject groups. Five active microphones in the array can provide an additional improvement at 45° of approximately 1 dB, relative to the three-microphone configuration for normal-hearing listeners.
These improvements in signal-to-noise ratio can be of great benefit for hearing aid users, who have difficulties with speech understanding in noisy environments.