Hearing Health Guide
Definition
A hearing threshold is the minimum sound level required for a person to detect a tone at a specific frequency in at least 50% of test trials. It is measured in decibels hearing level (dB HL), where 0 dB HL represents the average threshold of young adults with clinically normal hearing. The hearing threshold at each frequency is the core data point plotted on an audiogram.
During a standard hearing test (pure-tone audiometry), the audiologist plays tones through headphones at specific frequencies: typically 250 Hz, 500 Hz, 1,000 Hz, 2,000 Hz, 3,000 Hz, 4,000 Hz, 6,000 Hz, and 8,000 Hz. The volume is adjusted up and down using a standardized procedure (typically the modified Hughson-Westlake method) until the softest audible level is identified for each frequency.
The threshold at each frequency is the lowest level at which the person responds to the tone in at least two of three presentations. This is repeated for each ear separately.
Normal adult hearing thresholds are generally 0-25 dB HL across all tested frequencies, per AAA and ASHA classification standards. A threshold of 0 dB does not mean silence. It means the ear can detect the faintest sounds that statistically normal hearing can detect.
In practice, healthy young adults often have thresholds in the 0-10 dB range. Thresholds above 25 dB at any frequency indicate some degree of hearing loss at that pitch.
When the hair cells of the cochlea are damaged by noise, aging, disease, or medication, the threshold at affected frequencies rises. A higher threshold means a louder sound is needed before it can be detected. On an audiogram, damaged thresholds appear lower on the chart (further from the top).
Hearing loss due to noise exposure or aging typically elevates thresholds at high frequencies first (4,000-8,000 Hz) before affecting the speech frequencies (500-2,000 Hz). This is why high-frequency hearing loss often goes undetected for years. Conversational speech is still accessible while fine consonant discrimination gradually degrades.
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