A/B or dual-source switching is a convenient feature that allows flexibility when you're designing your whole-house audio system. With A/B switching, you can connect two sets of speakers and one source, and those speakers can be in same room or separate rooms. For example, speakers connected to source A could be in the living room and speakers connected to source B could be in the dining room. Then simply use the A/B switch to choose between the zones. 

Speakers are specified by impedance, which is a measurement of resistance to alternating current, and a common value for speakers 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. The SVC100 allows you to 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. Keep in mind that 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.