Spectral Characteristics of Air and Bone Conduction Transducers used to Record the Auditory Brain Stem Response

Abstract

This study sought to determine differences in the acoustic spectra of five different transducers commonly used for stimulus presentation to record the auditory brain stem response (ABR). The outputs of three commercially available bone conduction vibrators (Radioear B-70A, 8–71 and B-72), a TDH-49 earphone, and an insert receiver were measured by applying a 0.1 msec rectangular electrical pulse to each transducer. The resultant output for each transducer was converted to one-third octave band data and plotted against reference threshold levels. Results demonstrated relatively flat acoustic spectra and high output levels for the two air conduction receivers. In contrast, each of the bone oscillators had its greatest concentration of energy in the 2000 Hz region with the spectrum characterized by a precipitous decrease in output at frequencies above and below this resonance peak. Maximum output never exceeded 35 dB HL for any of the three bone conduction devices. Of the three oscillators, however, the B-70A appeared to provide the highest output before reaching saturation. Results are discussed relative to the limitations for recording the auditory brain stem response to bone conducted transient signals.