you cant "bridge" a mono amp...its already done inside the amplifier....as far as the dual 4 ohm sub goes.....you can wire the sub by bringing it up to 8 ohms and bring it back to 4 ohms at the amp...say on a mtx thunder they have 2 + and 2 - output speaker lines....it doesnt make any sense though...the best scenario would be a dual 2 ohm sub and having the same thing done with the sub and presenting the amp with a 2 ohm load....you get almost double the power from 4 ohms to 2 ohms...just my .02
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