Authors: Gilles Courtois¹
¹Sonova AG
Background: Increasing evidence suggests that low-gain hearing aids can benefit individuals with subclinical hearing loss (SCHL). In 2025, the National Acoustic Laboratories released the NAL-NL3 fitting formula, including a Minimal Hearing Loss (MHL) module. This module prescribes gain partly independent of the audiogram and recommends occluding ear coupling to maximize the efficacy of directional microphones and noise reduction features, marking a shift from traditional open-fit approaches for mild losses.
Method: Objective SNR benefits were evaluated using hearing aids fitted on a KEMAR manikin according to the **NAL-NL3 MHL** module. Using the Hagerman & Olofsson method, two Ambisonic scenes from the ARTE database were reproduced via a 12-loudspeaker array. The study analyzed the effects of three noise reduction tiers (representing different price points) and three dome types (open, vented, and power).
Results: The most advanced performance level, utilizing AI-based noise reduction, provided up to 4 dB greater SNR improvement compared to entry-level deterministic noise reduction. Furthermore, results confirmed that a significant portion of the SNR benefit is lost when using open domes instead of power domes, validating the recommendation for more occluding couplings to preserve advanced signal processing benefits.
Conclusion: The findings suggest that the NAL-NL3 MHL module is a promising tool for improving speech understanding in noisy environments for those with SCHL. To achieve optimal SNR benefits, the results highlight the necessity of advanced AI-based noise reduction and the use of the most occluding domes tolerable by the user.
