"Elvex Level Dependent muff uses the same technical components and features (including impulse filter) as Elvex Com-550, but the electronics is tuned for continuous industrial noise, and the muff is a non foldable construction|The communications features allow you to have close range communications in select continuous noise environments. The microphones on the outside of the ear muffs ""listen to"" the environment and can amplify weak sounds, and the gain limiter|Frequencies below 400 Hz and above 4,000 Hz are not processed and therefore the speech to noise ratio can be improved in many continuous noise environments.|An impulse (or impact) filter electronically eliminates impulse sounds by closing down the circuitry in four milliseconds, and opening the circuitry againin about 1/4 second (in order to prevent echo effect). The gun shots are eliminated, but the sho|An audio jack (3.5 mm jack) for connection of MP3 players and radios is standard. This jack willprovide listen-only capability (not two way communications). You can hear both the auxiliary device and Com-655.|Com-655 uses two 1.5 Volt AAA batteries. Batteries are included. The headset will operate for approximately 175 hours on one set of batteries, under normal circumstances. Reception is stereophonic.|An auto off switch will turn off the headset after four hours of continuous use, in order to conserve battery use."