AGC circuit , monitor area reach 150 sq.m. Hi-Fi circuit , even more natural voice. Automatic restrain high intensity's voice, dependable protect behind hold equipment Effectively decrease serious echo in open room by concave antrum. The patent that long distenced transmission (Audio cable Max. 3km). Audio monitoring cable: 4 cores line, network's twisted pairs, shield cable average can usage. Widely working temperature range (-25℃ ~ 75℃). Built-in lightning stroke protection and power protection circuit. Built-in preamp, direct drive speaker,recorder, DVR,VCR.