Variations in the feedback of hearing aids

Area of Science:

• Audiology and Hearing Aid Technology
• Acoustics and Signal Processing

Background:

• Hearing aid performance can be affected by various factors, including jaw movements, external acoustic conditions, and vent size.
• Both Behind The Ear (BTE) and In The Ear Canal (ITEC) hearing aid designs were investigated for response variations.

Purpose of the Study:

• To identify and quantify variations in hearing aid loop response due to external acoustic changes and vent dimensions.
• To compare the feedback characteristics of different vent designs using a theoretical model.

Main Methods:

• Investigated variations in loop response for BTE and ITEC hearing aids under different conditions, including jaw movement and external acoustics (e.g., telephone use).
• Utilized a theoretical model to analyze the feedback path and compare vent variations with measured data.
• Compared feedback levels for different vent lengths (12 mm vs. 24 mm) with equivalent low-frequency acoustic impedance.

Main Results:

• The largest external acoustic variations were observed with ITEC hearing aids when a telephone was used near the ear.
• Variations in loop response due to vent size changes were analyzed against a theoretical feedback path model.
• Theoretical calculations indicated lower feedback for shorter vents (12 mm) compared to longer vents (24 mm) when acoustic impedance was matched.

Conclusions:

• Jaw movements, external acoustics, and vent size significantly influence hearing aid loop response.
• ITEC hearing aids are more susceptible to external acoustic variations, particularly during telephone use.
• Shorter hearing aid vents may offer an advantage in reducing feedback compared to longer vents of similar acoustic impedance.