... bank counter 2)Durable and Stable 3)Clear and clean Interphone System DJJ-001 for bank counterA good channel between ... whistle and interference:Adopting a special auto-control channel, the interphone can prevent effectively electrics and acoustics whistle and interference. ... noise is no feedback echo for wide-ranging interphone. And for narrow-ranging interphone, if over 30 seconds no speaking, the ...