Benefits of low-frequency attenuation of baha® in single-sided sensorineural deafness

To investigate the effect of low-frequency attenuation of Bone-Anchored Hearing Aids (Bahas) in users with single-sided sensorineural deafness (SSD). The underlying notion is that low-frequency sounds up to approximately 1500 Hz reach the contralateral ear without significant attenuation and that Bahas tend to show more distortion at lower frequencies. Furthermore, to transmit low frequencies, higher moving masses are needed when compared with high frequencies.

A prospective study with 10 adults, experienced Baha Divino users with SSD. Speech understanding in noise was measured without Baha and with Baha, with three different settings of low-frequency attenuation, namely up to 270, 630, and 1500 Hz. Tests were performed in two different spatial arrangements. In one placement, speech was emitted from a loudspeaker on the side of the Baha ear and noise from a loudspeaker in front of the listener (S90N0). In the other placement, the sound sources were switched (S0N90). Participants rated the subjective sound quality of the two most extreme Baha settings using analog visual scales after a short acclimatization time of 15 mins.

In setting S90N0, the use of a Baha improved speech understanding in noise significantly (average improvement 2.8 to 3.1 dB, p = 0.006). These improvements did not vary significantly with the chosen low-frequency attenuation. In setting S0N90, a smaller but detrimental effect of the Baha was found (-0.9 to -1.7 dB, p = 0.006 to 0.03). This detrimental effect was significantly smaller at the highest cutoff frequency of 1500 Hz than at 270 Hz (p = 0.013). At the cutoff frequency of 270 Hz, loudness and reverberation were judged higher than at 1500 Hz. There was no significant difference in brightness, softness, clarity, or fullness.

High cutoff levels of up to 1500 Hz for low-frequency signals do not compromise the benefit of Baha in SSD for noise arriving from the front and speech presented on the side of the Baha. If noise is presented from the side of the Baha, the detrimental effect on speech understanding can be reduced by higher cutoff frequencies. If frequencies <1500 Hz do not need to be transmitted, lower moving masses of the Baha are required and smaller devices for patients with SSD may be possible.