You can mix and match speakers with different wattage ratings, but the lowest wattage speakers are the weak link if your amp is too powerful. It's the sensitivity rating that determines if speakers will be louder than other speakers. Same sensitivity, same loudness at a given amount of power. As for ohms, there are three ways to wire up a 4x12: Series, parallel, and series/parallel. Series is simple. Just add up the ohmages. Parallel for four speakers, the total effective ohmage is determined by the Formula: RT = 1 / (1/R1 + 1/R2 + 1/R3 + etc..) RT is Resistance Total. R1, R2, R3, and R4 are the ohmages of the individual speakers. Series-parallel is the most common setup. Two speakers are in series, added together, the other two are in series, added together. These two pairs are in parallel. Four speakers of the same ohmage in series-parallel have the same equivalent resistance as one speaker. Four 16 ohm speakers in series-parallel is a 16 ohm cabinet. Four 8s in series-parallel is an 8 ohm cabinet. Four 8s in series would be 32 ohms. Four 8s in parallel would be 2 ohms. Four 16s in parallel would be 4 ohms. Two 8s and two 16s in series-parallel, if there's one of each type in each series string, then it's two 24 ohm strings in parallel, giving 12 ohms.