Usage: VoiceCrystai V-EX model is compatible with PSTN and USB VoIP. It has two expandable microphones and its speaker volume is bigger for large meeting rooms. Relative models: VoiceCrystal P. Functions & Features: Full-duplex conversation, crystal clear voice Best for the conference room within 20-60m2 and Microphones gather covers 5m Built-in 4 microphones and 2 expandable microphones Support within 15 attendees DSP based deep Echo cancellation>-60dB Noise suppression>-20dB Bi-directional noise suppression purifies voice signal from both parties. Comfort Noise generation for conversation Hypercardioid directional microphone plus AGC automatic gain control satisfy group conference Hi-Fi audio amplifier and rare-earth Neodymium magnet speaker LCD with Caller ID Convenience redial,on hold,mute and rapid-dial SonicClear patented voice processing technology Compatible with PSTN analogy network and USB VoIP Easy installation