12 Pair Speaker Selector, Impedance Matching PRO-12 HP The PRO-12HP is a robust, efficient dual-source speaker selector for up to 12 pairs of speakers. Designed for demanding applications, this high-quality speaker selector features a low-frequency protection circuit to reduce subsonic signals. This allows higher power operation without amplifier shutdown.An A/B switch on the front panel allows you to power all your speakers with either of two source amplifiers. The PRO-12HP is designed for use with either 4- or 8-ohm speakers.The PRO-12HP uses audiophile-grade autoformers for impedance matching to maintain a safe operating load at the amplifier while distributing maximum power throughout your system. A rotary switch on the rear panel sets the appropriate impedance for your amplifier, based on the number of speaker pairs connected.