This patented technology provides two types of protection. Insert the black end for a constant NRR of 22dB. This is especially suited to all high level noise and reverberation such as in an indoor range. With the yellow end inserted, the patented filter takes over to provide variable level protection for impulse noises without blocking normal communications such as range commands. Noise reduction increases with level for weapons fire above 110dB. (estimated NRR's from about 0 to 22dB).