SUPRA-AURAL HEADPHONES
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These devices test air conduction, meaning that they measure the entire auditory system. Instead of circling around the ears, this device rests over the them, without them being completely enveloped (Moore). A typical model of supra-aural headphones used for testing in the sound booth is TDH-50, and such device tests within the frequency range of 250-8000Hz.
CIRCUM-AURAL HEADPHONES
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Circum-aural headphones, much larger than the device above, test frequencies across the entire auditory system and have much better fidelity than many of the other devices; they cover the entire exterior of the ear while testing, massively decreasing background noise. Circum-aural headphones, such as Sennheiser HDA200, test ultra high frequencies ranging from 9,000-20,000Hz, and are typically used for special populations, like patients with complaints of tinnitus or those exposed to ototoxic drugs such as chemotherapy (Murphy).
INSERTS
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Inserts are a frequent option for patients who are irritated by devices covering their ears or those with abundant ear piercings, as they're placed inside of the external auditory meatus. Inserts test the entire auditory system and measure frequencies ranging from 500-4000Hz, examples of insert models include ER-3A and ER-3C (Moore). The foam tips reduce background noise while comfortable resting inside of the patient's ear canal.
LOUDSPEAKERS
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Loudspeakers are a great option for those who can not tolerate headphones or inserts during testing, and may require a more hands off approach. They're typically used for pediatric patients or those who are behaviorally difficult to test, and they measure the entire auditory system through sound field testing. Not only this, but they can also be used to asses an individual's hearing aids, in which we can put the aid in, amplify sounds in the booth, and test whether or not the device is working to the best of its ability (Jung).
BONE OSCILLATOR
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Unlike the other transducers, a bone oscillator tests through bone conduction, meaning that it bypasses the outer and middle ear, and sound is delivered directly to the inner ear through the mastoid (What). Although it's not the most comfortable of the devices, the square box fixed at the end of the headband is placed over the mastoid and produces sound signals through vibrations directly to the inner ear, testing for frequencies ranging from 250-4000Hz.