NAL-NL2 Prescriptive Targets for Bone Conduction Devices With an Adaptation to Device Constraints in the Low...

Area of Science:

• Audiology
• Hearing device technology

Background:

• Percutaneous bone conduction devices (BCDs) require effective gain prescriptions.
• The NAL-NL2 (National Acoustic Laboratories - Nonlinear, version 2) is a widely used hearing aid gain prescription.

Purpose of the Study:

• To evaluate the efficacy of a transformed NAL-NL2 gain prescription for BCDs.
• To determine optimal output constraints for low frequencies in BCD fittings.

Main Methods:

• Adapted the NAL-NL2 prescription for BCDs, creating three settings with varying low-frequency gain and compression.
• Evaluated sound quality and speech intelligibility in 18 experienced BCD users across different sound stimuli.

Main Results:

• Sound quality preferences varied by stimulus; more low-frequency output was preferred for music, less for the user's own voice.
• Speech intelligibility in quiet was lower with reduced low-frequency gain (S3).
• Speech intelligibility in noise was reduced across settings, but S3 showed better performance than S1.

Conclusions:

• A transformed NAL-NL2 prescription with moderate low-frequency gain reduction is suitable for BCD fittings.
• Optimal adaptation balances audibility and device constraints, with moderate low-frequency reduction showing neutral to positive sound quality and no negative impact on speech intelligibility.
• The NAL-NL2-BC provides adequate gain as confirmed by speech tests.