Air-radiated sound from bone vibration transducers and its implications for bone conduction audiometry

The effect of air-borne sound radiated from transducers used in bone conduction audiometry has been known for many years. This paper seeks to quantify this effect for the vibrator types (B70A, B71, and B72. Using three examples of each vibrator sound pressure levels were measured at the entrance to the external ear canal on four human heads. Values obtained have been related to hearing theshold levels for otologically normal young persons using two different methods: firstly using international standard values of open-ear free-field theshold with corrections for monaural listening and for diffraction, and secondly by direct measurement of the subjects' monaural open-ear thresholds. None of the vibrators tested meets international standard requirements for air-borne sound radiation at all frequencies, but in practics, provided a high quality ear plug is fitted to the test ear at 3 and 4 kHz large errors are unlikely to be recorded for any of the vibrator types tested.