Great solution for collector or vintage cars where keeping the dash stock or unaltered is a must. Also a great solution for Boats, Motorcycles, Gulf carts and Side by side Atv's. Hidden Bluetooth receiver with built in amplification with hands free calling capabilities. Mark 4 is for use with up to 4 speakers, pre - amp outputs for external amplification or subwoofer and comes with a microphone for hands free calling capabilities.