Effect of Head Coverings on Directional Microphone Performance in Modern Hearing Aids: A KEMAR-Based Laboratory Evaluation
TL;DR
No statistically detectable overall covering effect was observed across the four tested hearing aid devices; however, covered–uncovered differences varied by device and frequency, and the absence of statistical significance should not be interpreted as evidence of equivalence between covered and uncovered conditions.
Abstract
Background/Objectives: Directional microphones are an established hearing aid technology for improving speech understanding in background noise. Although researchers have examined the influence of hair, spectacles, and earmold venting on directional performance, no systematic work has addressed head coverings, which people wear worldwide for cultural, religious, occupational, and personal reasons. This study determined whether a cotton head covering alters the directivity index (DI) of highest-level receiver-in-canal (RIC) hearing aids. Methods: A Knowles Electronics Manikin for Acoustic Research (KEMAR) was positioned in a double-walled, sound-treated booth, and DI was measured for omnidirectional and fixed directional microphone settings, with and without a two-layer cotton covering placed over both microphone ports. We presented frequency-modulated tones at 500, 1000, 2000, and 4000 Hz at 60 dB SPL from a loudspeaker positioned 1 m from KEMAR, with all adaptive features disabled. We recorded root-mean-square levels at 30° increments and analyzed DI using a 2 × 2 × 4 repeated-measures analysis with microphone mode, head covering condition, and frequency as within-device factors. Covered–uncovered differences (ΔDI_H) were reported with 95% confidence intervals. Results: Fixed directional processing produced a mean horizontal-plane DI 1.50 dB greater than omnidirectional processing across the four tested hearing aid devices; however, this difference did not reach statistical significance when the hearing aid device was treated as the independent experimental unit, F (1,3) = 7.57, p = 0.071, partial η2 = 0.716. The overall covered–uncovered change was small (mean ΔDI = −0.023 dB, 95% CI: −0.193 to 0.148 dB; p = 0.699). The head covering × frequency interaction was not statistically significant after Greenhouse–Geisser correction (p = 0.301), nor was the head covering × microphone-mode interaction (p = 0.860). DI varied significantly across frequency (Greenhouse–Geisser adjusted p = 0.030). We did not perform inferential comparisons among hearing aid devices because only one system represented each manufacturer. Conclusions: No statistically detectable overall covering effect was observed across the four tested hearing aid devices; however, covered–uncovered differences varied by device and frequency. Given the small number of independent devices, the absence of statistical significance should not be interpreted as evidence of equivalence between covered and uncovered conditions. The findings are specific to the lightweight cotton configuration and laboratory conditions evaluated.