A method to measure hearing aid directivity index and polar pattern in small and reverberant enclosures.

OBJECTIVE

The directivity index (DI) and polar pattern of directional hearing aids are typically measured in an anechoic chamber, which is expensive and not commonly found. This article proposes a quasi-anechoic technique to measure hearing aid directivity in small and reverberant enclosures using the root-mean-square amplitude of the first 3 ms of the hearing aid's response to the input signal.

DESIGN

The hearing aid's planar DI and polar pattern were measured using the proposed method in an audiologic booth with low reverberation, a room with moderate reverberation, and an anechoic chamber. The measurement was repeated four times for each aid in each environment. The results were compared to the directivity obtained in the anechoic chamber using two benchmark measurements.

STUDY SAMPLE

Eight hearing aids with a fixed directional mode were tested.

RESULTS AND CONCLUSIONS

The results revealed that the error of the proposed method in DI was smaller than 0.3 dB in 94% of the measurement conditions. The standard deviation of the DI was smaller than 0.1 dB in 94% of the conditions. These results suggest that the proposed quasi-anechoic method provides an accurate and repeatable way to assess non-adaptive directional microphone hearing aids in small non-anechoic enclosures.