Active noise reduction technology for hearing protection

Occupational Health & Safety magazine recently reported on single and double hearing protection and on new active noise reduction (ANR) technology, which underlies triple hearing protection. According to the US Occupational Safety and Health Administration (OSHA), hearing protectors must reduce an employee’s 8-hour time-weighted average noise exposure to no more than 90 dB(A), as a basic guide.

Hearing protectors such as earplugs or earmuffs generally provide a reduction of about 10 dB which meets the OSHA requirement in most working conditions. Double hearing protection, i.e. the use of two different hearing protectors simultaneously, for instance earmuffs over earplugs, is recommended for average noise exposure at or above 105 dB(A).

In some occupational environments, where engineering controls are not feasible and double hearing protection is inadequate, time limits have been the standard protection approach. Active noise reduction uses high-speed processing capabilities and has been miniaturized and can now be placed deep in the ear canal. Typical ANR circuits contain a microphone, a controller and a speaker. The microphone measures the sound present in the occluded space between the tip of the ear plug and the eardrum, the controller processes the signal and generates an “anti-sound” that is delivered to the occluded space by the speaker. This effectively cancels out the noise.

Source: Occupational Health & Safety