Hearing Health Guide
Definition
Hearing threshold level (dBHL) is the unit of measurement used on clinical audiograms to express the softest sound a person can detect at a given frequency. A threshold of 0 dBHL represents the average threshold of a large population of normal-hearing young adults at that frequency, not absolute silence. Each additional 10 dBHL represents a tenfold increase in sound pressure.
During pure-tone audiometry, the audiologist presents tones at progressively softer and louder levels until the softest level the patient detects 50% of the time is established. This is the threshold. The process is repeated at each test frequency (typically 250, 500, 1,000, 2,000, 4,000, and 8,000 Hz) for each ear.
Thresholds are measured separately for air conduction (through headphones) and bone conduction (through a skull vibrator). Comparing the two determines the type of hearing loss.
0-25 dBHL (Normal): detects soft sounds typical of quiet environments. 26-40 dBHL (Mild): whispered speech and soft consonants become inaudible in many situations. 41-55 dBHL (Moderate): conversational speech at normal volume becomes unreliable. 56-70 dBHL: Moderate-severe. 71-90 dBHL: Severe. 91+ dBHL: Profound.
The significance of a given threshold depends on the frequencies affected. Loss at 2,000–4,000 Hz has a disproportionate impact on speech intelligibility because this is where many speech consonants concentrate.
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