OSD Audio’s VMS300 is an impedance-matching volume control for adjusting the volume of a pair of speakers within a whole house audio system. Ideal for dining rooms, saunas, porches or other areas of the house where you want to add sound, the VMS300 maintains the full hi-fi audio frequency response with no low frequency roll-off and is equipped with the same features of volume controls that cost twice as much. Rated at 300 Watts peak, the volume control includes adjustable jumpers to add up to eight pairs of 8-ohm speakers simultaneously, and the impedance-matching feature helps stabilize the ohm load going back to the amp or receiver to avoid overheating. This is a complete volume control kit that fits into a standard single-gang box and includes the VC, junction box, screws and assorted color trim plates (white, ivory and almond) so you can choose the color that best matches the room. Compatible with almost any dedicated audio zone or whole house system, the electronics inside the VSM300 are designed with a ruler-flat frequency response while the 12-step slider provides noise-free volume control and a wide range of listening volumes.

Impedance is a measurement of resistance to alternating current. Speakers are specified by impedance, and a common value is 8 ohms. When you’re connecting multiple speakers to a receiver or amplifier, you need to stay above the amp’s minimum load requirements because going below the impedance rating can overheat or even damage expensive equipment. Volume controls such as the VMS300 have selectable impedance so you can match the impedance with the number of speakers being controlled with the capabilities of your amp. A basic multi-room system will typically have an amplifier/receiver, a speaker selector, four to eight pairs of speakers, and volume controls. Impedance-matching volume controls feature three settings depending on how many speakers you are connecting. For one to two pairs of 8-ohm speakers, the setting is 1/2x; for three or four pairs of 8 ohm speakers, the setting is 4X. Volume controls do not add gain (volume) to your speakers but simply attenuate the volume up or down. During setup, you'll set the source volume to its optimum level, then the volume control turns the sound down to inaudible levels.