Equivalent threshold force levels for skin drive bone conduction hearing devices

Introduction Bone conduction hearing devices (BCDs) are essential for individuals with conductive or mixed hearing loss who cannot use traditional air conduction devices. Prescriptive methods for skin drive BCDs have recently been developed, taking into account skin and soft tissue transmission loss. Equivalent Threshold Force Levels (ETFLs) are needed to define normative references and enable accurate prescription and verification yet are not well-established for skin drive BCDs. Methods In this study, in-situ thresholds were measured in 20 normal-hearing young adults using three commercially available skin drive BCDs, and corresponding force level outputs were recorded with a skull simulator to derive ETFLs. Results In-situ thresholds were significantly higher than audiometric bone conduction thresholds and varied by 2.7–15 dB across devices. After conversion to force levels, variability in measured thresholds between devices decreased but remained significant at select frequencies, with discrepancies of up to 17 dB. Discussion These results indicate that ETFLs can be defined for skin drive BCDs, although device-specific differences are observed. Establishing ETFLs provides a foundation for standardized prescription and verification methods, but may need to incorporate device-specific properties.