2-4 Passenger High Fidelity Stereo Intercom; NNT10 and NNT20 are identical, the only difference between the two is the chassis size. The Front Headset inputs are deactivated, must use rear Headset inputs for all riders. VOX Knob: Adjusts the voice activation sensitivity for the intercom, will soft mute music for speaking while activated, Volume Knob: Adjusts only the speaking volume when intercom is active/PTT, Separate Front Music Input: Universal 3.5mm input for music streaming only. (No Phone calls) Cell Input: 3.5mm input (STi3 Cable) for phone call/music PO/PTT LED: Power indicator (Blue) and Push to Talk indicator (RED) RF Shield Housing; High Level Output for Headphones for Sound Quality.