Ivo Leon Diane Marie Merks

Design of a broadside array for a binaural hearing aid

This paper describes the design and implementation of a binaural directional hearing aid. This hearing aid consists of a microphone array of five directional microphones integrated into the front of a pair of spectacles. The signals of the microphones are processed with the aid of double beamforming into a left-ear and a right-ear signal. The directivity pattern of the left-ear signal has its main lobe at a small angle to the left, and the directivity pattern of the right-ear signal at a small angle to the right. These different main lobes cause an interaural level difference (ILD). In natural conditions, an ILD enables the human auditory brain to localize sound sources and to significantly improve speech intelligibility in noise. A computer simulation and an implementation in analogue electronics show that the main lobes for the left-ear and right-ear realize sufficient ILD at high frequencies to enable an effective localization of sound sources.

How round is the human head

Binaural microphone arrays are becoming more popular for hearing aids due to their potential to improve speech understanding in noise for hearing impaired listeners. However, such algorithms are often developed using three-dimensional head-related transfer function measurements which are expensive and often limited to a manikin head such as KEMAR. As a result, it is highly desired to use a parametric model for binaural microphone array design on a human head. Human heads have been often modeled using a rigid sphere when diffraction of sound needs to be considered. Although the spherical model may be a reasonable model for first order binaural microphone arrays, recent study has shown that it may not be accurate enough for designing high order binaural microphone arrays for hearing aids on a KEMAR (Merks et al., 2014). In this study, main sources of these errors are further investigated based on numerical simulations as well as three-dimensional measurement data on KEMAR. The implications for further impro...

Estimation of maximum stable gain in a hearing aid

Feedback cancellation (FBC) algorithms have become an important part of hearing aids, allowing the Maximum Stable Gain (MSG) to be increased by up to 25 dB beyond what is possible without an FBC. Although FBC algorithms have improved the usability of hearing aids, it is difficult to predict the MSG for a given individual with a particular hearing aid. Knowledge of this information would enable the audiologist to make more informed decisions regarding the appropriateness of a hearing aid/earmold, and it could be used to counsel the patient regarding feedback. A method of estimating the MSG of a hearing aid with and without an FBC will be presented. The method uses a finite impulse response filter to approximate the acoustic path. The filter coefficients are estimated during the initialization of the FBC. From these filter coefficients, the MSG for the hearing aid with and without FBC are calculated. This method has been implemented in the firmware and fitting software. Using a variety of device styles, microphone modes and feedback paths, it has been verified that the estimated MSG matches the actual MSG within 6 dB for 90% of hearing aids.

Array technology for binaural hearing aid applications

An increasing number of people have great difficulties in understanding speech in noisy environments. These difficulties can be resolved with a directional microphone array which attenuates the background noise while it transmits the desired signals unaltered to the hearing aid. A highly directional endfire array has been developed containing only four omnidirectional microphones which are integrated into the arm of a pair of spectacles. Two endfire arrays, one per ear, devise a binaural hearing aid which further increases the speech intelligibility and also enables localization. The arrays realize maximum directivity with a least‐squares optimization of the array processing which also takes into account the diffraction effects due to the presence of the head. The microphone signals are processed with FIR filters to obtain maximum control over both the amplitude and phase of the transfer functions of the filters, thereby achieving maximum directivity. The microphone array attenuates the background noise o...