The intent of the Radial MC3 Monitor Controller is simple: Small studios need to switch between various studio monitors and a subwoofer. There are many controllers on the market. But most are expensive or worse yet, they color the sound of the audio signal. The MC3 is a passive device that switches the signal without introducing any circuitry. The power connection is used to toggle the internal relays, turn on some LEDs, sum the input to mono for the sub woofer and, of course, power up the headphones.