PURETONE AUDIOMETRY Audiometers are used to make quantitative measures of Air Conduction and Bone Conduction Pure Tone thresholds. AC thresholds assess the entire auditory pathway and are usually measured using earphones. When sound is delivered by an earphone, the hearing sensitivity can be assessed in each ear separately. BC thresholds are measured by placing a vibrator on the skull, with each ear assessed separately, usually by applying masking noise to the non test ear.