Investigation of a novel completely-in-the-canal direct-drive hearing device: a temporal bone study

Whether a prototype direct-drive hearing device (DHD) is effective in driving the tympanic membrane (TM) in a temporal bone specimen to enable it to potentially treat moderate-to-severe hearing loss.

Patient satisfaction with air conduction hearing aids has been low because of sound distortion, occlusion effect, and feedback issues. Implantable hearing aids provide a higher quality sound but require surgery for placement. The DHD was designed to combine the ability of driving the ossicular chain with placement in the external auditory canal.

DHD is a 3.5-mm wide device that could fit entirely into the bony ear canal and directly drive the TM rather than use a speaker. A cadaveric temporal bone was prepared. The device developed in our laboratory was coupled to the external surface of the TM and against the malleus. Frequency sweeps between 300 Hz to 12 kHz were performed in 2 different coupling methods at 104 and 120 dB, and the DHD was driven with various levels of current. Displacements of the posterior crus of the stapes were measured using a laser Doppler vibrometer.

The DHD showed a linear frequency response from 300 Hz to 12 kHz. Placement against the malleus showed higher amplitudes and lower power requirements than when the device was placed on the TM.

DHD is a small completely-in-the-canal device that mechanically drives the TM. This novel device has a frequency output wider than most air conduction devices. Findings of the current study demonstrated that the DHD had the potential of being incorporated into a hearing aid in the future.