By test results seen, they put out the most at 1 ohm, but it's the thermal that's not worth the 10 extra watts or so from 1 ohm to 2 ohms. IMHO, I say they're optimal at 2 ohms.iirc , the test ive seen , they put out more power at 4 ohm rather than 1 ohm. the increase is nothing to 'wow' about , but it is there.