Function: The system has the function of limiting the quantity of delegate unit,can choose the limit address type directly,such as "1,"2","3","5"or "all open".When choose "1"or "2" or "3" or "4" or "5",the delegate unit which opened at the same time can not excess the quantity choose,when reach the chosen quantity ,besides the delegate unit is turned off or the chairman unit press the key,or else the new delegate unit can not be opened,when choosing"1",it can answer before others. There is no limitation for the chairman unit;it can open at any time. Press the preferential key to close the whole delegate units which need to re-press the key to speak. Every conference main unit can drive up to 60 units,and can drive over 200 units by adding expansion main unit. Built-in the telephone coupler,it can open a telephone conference with remote user. Internal feedback restraint circuitry.set up alt/bourdon digital adjust circuitry,so as to adjust system's timbre independently;also can adjust the volume. Equipped with balance circuitry output interface,left/right circuitry output interface,unbalance output interface,so as to adapt the connection of each kind of equipments. Use the imported Panansonic microphone cartridge.The distance from microphone is up to 450-500mm and without howling.(matching with the same brand equalizer to use) Main unit parameter: Power supply: AC100V-240V 50Hz/60Hz Output power:115w/18v each channel Statics power consumption: 8w Audio input interface:8PIN DIN *3 Audio output interface:1.XLR(male)*1, 2.1/4"(TRS)*3 SNR:>80dB Microphone input impedance:100K ohm Audio frequency response:60-10KHz THD:<0.5% Overload distortion:<1% Color:black External dimension(mm):(L)485*(W)260*(H)98 Installation:19-in standard rack(2U) Weight:9.5kg