Frequency is measured in Hz, which are cycles per second. Some children can detect even higher frequencies. This test assesses sensitivity when the signal is transmitted through the outer, middle, and inner ear and then through the brain to the cortex. Testing may be performed using headphones, insert earphones, or sound fields. Headphones are placed over the outer ear.
Circumaural headphones have a large cushion and fit around the ear, contacting the head.
These generally are used to reduce ambient noise. Supraaural headphones are more common and rest on the ear or pinna, but they typically provide no ambient noise reduction and may collapse the ear canals. The signal is transmitted down a tube to foam tips, which fit in the ear canal. Insert earphones help reduce collapsing ear canals, and they reduce some ambient noise and crossover of auditory stimuli to the nontest ear via skull transmission. This form of testing is used with infants, toddlers, or other individuals with special needs for whom earphone use could be problematic.