Air Conduction Thresholds

Air conduction thresholds are hearing thresholds measured by presenting sound through headphones or insert earphones placed in or over the ears. Sound delivered via air conduction travels through the outer ear canal, causes the eardrum to vibrate, passes through the middle ear ossicles, and reaches the cochlea through the oval window. Air conduction thresholds therefore reflect the function of the entire auditory pathway: the outer ear, the middle ear, and the inner ear together.

In a standard hearing assessment, the audiologist measures air conduction thresholds at frequencies from 250 Hz to 8,000 Hz in each ear. The person being tested responds whenever they detect a tone, and the audiologist adjusts the intensity in small steps to find the softest audible level at each frequency. These thresholds are plotted on the audiogram and form the primary picture of a person's hearing ability across the speech frequency range.

Air conduction thresholds are always compared to bone conduction thresholds during assessment. When air and bone conduction thresholds are similar (within 10 dB), any hearing loss present is sensorineural, meaning the inner ear or auditory nerve is the site of the problem. When air conduction thresholds are significantly poorer than bone conduction thresholds, an air-bone gap exists, indicating that the outer or middle ear is not transmitting sound normally and a conductive component is present.