Sound level meters measure at discrete times, while dosimeters measure continually over time for a more accurate estimate of risk.
Yellow (Borderline): Noise dose is greater than 50% and less than 100%
Red (High Risk): Noise dose is greater than 100%
Hearing loss from loud sound affects millions of people. Noise-induced hearing loss is preventable, but most people don’t know how long they can listen to loud sound without risking hearing damage. A single noise exposure may not result in hearing loss, but permanent damage to the inner ear from noise adds up over time. The accumulation of too much noise day by day, year after year, is the determining factor in hearing loss risk. A sound level meter is a device that measures noise at a particular point in time, while a dosimeter measures sound levels for many hours and calculates the cumulative noise dose in percent.
Daily noise dose is determined by both the intensity of the sound and the amount of exposure time. A 100% dose means that a person has reached the maximum noise exposure for the day, and continued exposure to loud sound could lead to hearing loss. Ideally, hearing protection should be used before the dose reaches 100% since dose limits are based on averages, and some ears are more susceptible to noise damage than others. When the noise dose exceeds 50% a person has reached half the maximum noise exposure for the day and it’s a good idea to use hearing protection to prevent over-exposure, particularly if a 50% dose reading is reached early in the day.
In cases of gunfire and other impulse noise, no conventional dosimeter measures the risk accurately. More specialized equipment is required to measure impulse noise.