The SDB-4.1 is a highly efficient dual-source speaker selector that controls up to four pairs of speakers. The front panel provides a separate volume control for each speaker pair, allowing you to adjust the volume in each room from one convenient location. With two amplifier inputs, the SDB-4.1 allows you to choose either program in each room. Each zone also has an on/off switch, which allows you to keep the volume control at a set level while turning the speakers on or off. The SDB-4.1 uses high-quality impedance-matching autoformers to maintain a safe operating load at the amplifier while distributing maximum power throughout your system. Designed for use with either 4- or 8-ohm speakers, the SDB-4.1 is equipped with internal jumpers to select the degree of impedance matching based on the impedance of your speakers and your amplifier's impedance requirements.