Maximum stable gain and fitting range of percutaneously applied bone conduction devices

to measure the maximum stable gain (MSG, the feedback limit) and its variability in users with two percutaneous power bone conduction devices (BCDs), to determine an MSG-based fitting range, and to measure the available aided dynamic range.

The MSG was determined with the BCD attached to a participant's head. The BCD output was measured on a skull simulator. A fitting range was derived using the speech intelligibility index.

42 adult BCD users.

The average and range of the MSG was 13.3 ± 3.2 dB for device 1 and 16.1 ± 5.90 dB for device 2. The fitting range is 35-40 dB HL for a good understanding of soft speech and 45-50 dB HL for moderate-to-sufficient understanding of speech at a normal level in at least 50% of the cases with this hearing loss. The output for common speech levels is not limited by the maximum force output, except at low frequencies.

For users of a percutaneous power BCD, the maximum applicable gain is limited by feedback and is smaller than the full-on gain. Consequently, BCDs enable sufficient speech intelligibility only for mild-to-moderate sensorineural hearing loss. The aided dynamic range is adequate for hearing thresholds within this fitting range.