and Ohm is just a unit of electrical resistance.
a watt is just a unit of power.
images courtesy of Wikipedia.org
The measure of resistance determines how much current (amperes) will pass through a load with a given voltage.
The difference between 60w at 4ohm and 75w at 2ohm is:
60w @ 4ohm requires 15.5v and that voltage moves 3.8a of current.
75w @ 2ohm requires 12.2v and that voltage moves 6.14a of current.
The difference? 75w is more power. Some argue that high voltage, low current is the best way to transfer power, which it is, but in our case it is such a short distance that it really doesn't matter.
2000 Mazda B3000 TL Edition 2wd
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*Eventually: Head Lights, More Tint, 5.0 swap, Murdered, Tube Bumpers, Off Road Lights, Body Lift, Better Stereo, More...