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

Abstract

Abstract

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.

Sumario

Objetivo: Típicamente el índice de direccionalidad (DI) y el patrón polar de los auxiliares auditivos direccionales son medidos en una cámara anecoica, que generalmente es costosa y difícil de encontrar. Este artículo propone una técnica quasi anecoica para medir la direccionalidad en un recinto pequeño y reverberante, utilizando el promedio de la raíz cuadrada de la amplitud de los tres primeros mili-segundos de la respuesta de los auxiliares auditivos ante la señal de entrada. Diseño: El patrón plano DI y el polar de los auxiliares auditivos fueron medidos utilizando el método propuesto en una cabina audiológica con baja reverberación, en un cuarto con moderada reverberación y en una cámara anecoica. Se repitieron las mediciones cuatro veces para cada auxiliar en cada condición ambiental. Se compararon los resultados con la direccionalidad obtenida en la cámara anecoica utilizando dos mediciones de referencia. Muestra: Se evaluaron ocho auxiliares auditivos en el modo de direccionalidad fija. Resultados Y Conclusiones: Los resultados revelaron que el error del método propuesto en DI fue menor a 0.3 dB en el 94% de las condiciones medidas. La desviación estándar del DI fue menor a 0.3dB en 94% de las condiciones de medición. Estos resultados sugieren que el método quasi anecoico propuesto proporciona una forma certera y repetible para evaluar auxiliares auditivos con micrófonos no adaptativos en un recinto no anecoico

Key Words::

• Directivity
• Hearing aid
• Directional microphone

Acknowledgments

This research was supported by Grant DoEd-NIDRR 84.133E-1 from the Department of Education/National Institute on Disability and Rehabilitation Research. The authors thank Don Hayes for his valuable information and comments. They also thank Dr. Michael Valente and two anonymous reviewers for their helpful suggestions and comments on an early version of this paper.

Note

1. With the distance between the sound source and the device under test set at 1 m, the desired low frequency band is 500 Hz, and the height of the sound source and device under test is set at 4 m. A room's floor and the roof are typically the surfaces nearest the sound source and the device under test.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.