ISRETROVC
If you want to play music in a room that doesn't need a Room Station, use the IST RETRO Volume Control to change the volume of external speakers (sold separately) that connect to your IST RETRO Music & Intercom System. This in-wall control has a rotary knob that allows you to adjust the volume of music and messages without a Room Station, plus a source button that lets you switch between the radio and MP3s.
The IST RETRO Volume Control installs in a standard single-gang box. It wires into your speakers with 16- or 18-gauge 2-conductor wire, and into your Master Station with the existing wiring (requires 3 wires).