Bone Conduction Calibration:  Bone Vibrator Characteristics

The IEC 373-1971 and ANSI S3.13-1972 (revised to ANSI S3.43-1992) have recommendations for the performance characteristics of a bone vibrator for bone conduction testing.  Bone vibrators with a circular contact tip with a surface area of 1.75 cm² is recommended.  The force against the mastoid should be 5.4 Newtons.  Unfortunately, most bone vibrators in the clinical setting do not meet these standards either because of difficulty positioning the device on clients heads or variation in head sizes resulting in different contact force.  

The Radioear B-71 and B-72 bone vibrators coupled to the Radioear P-3333 headband were developed to meet both current IEC and ANSI standards.  Billings et al (1977) conducted a study to test the characteristics of three common bone vibrators (Radioear B-71, B-72, and B-70A).  Below is a simplified summary of their results.   

Data taken from Billings et al 1977.

Audiologists may already know that although the Radioear B-71 and B-72 provide a better performance match to the ANSI and IEC standard, they are extremely difficult to position on the mastoid process accurately (they tend to slip off).  Billings et al. (1977) emphasis that the B-70A (coupled to the Radioear P-1123-B headband) is still the easiest vibrator to use in the clinical setting.  Audiologists who opt to continue using the B-70A need to be aware that it does not meet the IEC and ANSI standard for force against the mastoid. 

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