Hearing Threshold
A hearing threshold is the softest level at which a person can detect a sound at a given frequency 50 percent of the time under controlled test conditions. It is measured in decibels hearing level (dB HL). In pure tone audiometry, thresholds are established by presenting tones at various frequencies and adjusting the intensity until the person can just barely detect the sound.
A threshold of 0 to 25 dB HL is considered within normal limits for adults. A threshold above 25 dB HL at any frequency indicates some degree of hearing loss at that pitch. Thresholds plotted across frequencies on an audiogram give a complete picture of a person's hearing profile. Thresholds can differ between ears, at different frequencies, and under different test conditions.
Air conduction thresholds (measured through headphones) reflect the entire auditory system. Bone conduction thresholds (measured through a vibrating device on the skull) reflect inner ear function specifically. Comparing the two helps identify whether hearing loss is conductive, sensorineural, or mixed.
