This speaker cabinet is made for the ST-Stereo or the Stereo Master 20 heads. However, it could be used with two separate heads or one head with two outputs. The Speakers are 2 celestion creambacks, 8 ohms each. In the stereo setup you would use 8 ohms on the head to match with the speaker. If you have a mono head that has two outputs and you want to run into the Stereo speaker cabinet you would need to run two speaker cables and set the impedance on the amp to 4 ohms.