Nowadays, many different kinds of bone-conduction devices (BCDs) are available
for hearing rehabilitation. Most studies of these devices fail to compare the
different types of BCDs under the same conditions. Moreover, most results are
between two BCDs in the same subject, or two BCDs in different subjects failing
to provide an overview of the results between several of the BCDs. Another issue
is that some BCDs require surgical procedures that prevent comparison of the
BCDs in the same persons. In this study, four types of skin-drive BCDs, three
direct-drive BCDs, and one oral device were evaluated in a finite-element model
of the human head that was able to simulate all BCDs under the same conditions.
The evaluation was conducted using both a dynamic force as input and an electric
voltage to a model of a BCD vibrator unit. The results showed that the
direct-drive BCDs and the oral device gave vibration responses within 10 dB at
the cochlea. The skin-drive BCDs had similar or even better cochlear vibration
responses than the direct-drive BCDs at low frequencies, but the direct-drive
BCDs gave up to 30 dB higher cochlear vibration responses at high frequencies.
The study also investigated the mechanical point impedance at the interface
between the BCD and the head, providing information that explains some of the
differences seen in the results. For example, when the skin-drive BCD attachment
area becomes too small, the transducer cannot provide an output force similar to
the devices with larger attachment surfaces.