Bone conduction calibration: current status.

Attempts to specify normal threshold sensitivity by bone conduction have been unsuccessful because of problems in obtaining reliable measurements from commercially available artificial mastoids. Recent design modifications incorporated in the Bruel and Kjaer 4930 artificial mastoids have resulted in greater uniformity among these units. However, the new design has resulted in impedances that are higher than those recommended in current standards. Bone-conduction thresholds referenced to measurements made on B & K 4930 artificial mastoids with the new design were performed on 60 normal listeners by three participating laboratories. The results are reported for consideration in the development of a reference threshold for hearing by bone conduction.