The PT-4 speaker selectors accommodates up to 4 pairs of speakers. The controls of the PT-Series allow you to play any combination of speakers simultaneously. Automatic Autoformer Protection constantly processes how many speakers are selected and provides the purest possible path from the amplifier to the speaker. As you engage more pairs of speakers, the PT- Series gradually inserts autoformer protection, constantly striving to keep the maximum power flowing to your speakers. No "Protection Buttons". Autoformer protection is automatically inserted each time a room is turned on. Five times the power of resistive selectors when all rooms are on.