The Howard Leight Electronic NRR 30 Impact Pro Noise Reducing Ear Muff Headphones R-01902 amplifies low level sounds more than 4 time for incredible reduction in the sounds that you don't want to hear while amplifying the ones you do. The aggressive earcup design and rubberized pressure points on this Ear-Muff from the experts at Howard Leight provides the user with additional durability. The Howard Leight NRR 30 Impact-Pro Earmuffs have an External Audio Jack connects to any music or audio source including, MP3 players, smartphones, or scanner radios. This Howard Leight Noise Protection actively listens and automatically shuts off amplification whenever harmful sound levels are reached. The Howard Leight Electronic Impact Pro Automatic Shutoff Ear Protective Headphones feature Air Flow Control Technology (AFC) that enables you to hear normal conversation while delivering protection at high frequencies.