Well, let's see. I'm gonna make a couple of assumptions. One is, that if your guitar player uses a Plexi, he likes to turn it up. (Right?) Then the next one is, you're also playing with a loud drummer. If you're in a situation where you find yourself having to compete with these guys to turn up loud enough to make them sound good (wink), then I'd say target 300 watts for a tube amp, and 1000 watts for a solid state amp.
After that, it's a question of what kind of sound you're after. If you want the SVT sound, you have to get an SVT and an SVT cabinet. Or if you want the 370 sound, then it's an Acoustic 370 and a 301 cabinet.
Personally, I prefer the more dynamic punchy sounds. I do a lot of slappin' stuff, but I also play in a classic rock and blues cover band, so those are two different types of requirements. For both, I like nice deep rich "fat" low end, and a nice dynamic punchy high end. But for the slap stuff I need power in the extreme lows and extreme highs, whereas for the classic rock and blues stuff I need power in the lower midrange. Here's what I've found.
If you're playing outdoors, there's no substitute for big speakers. I use EVX-180A's to get my sound "out there" into the audience. In an outdoor situation, the low frequencies travel through the ground, and it takes beaucoup power and very big speakers to make that happen. The same would apply in a large indoor venue where you're basically playing to a lot of open space. Usually those big 18's don't have a whole lot of high end, so I complement that with a bunch of 12's to get some decent upper midrange, and that also gives me the punchy high end I'm looking for. That's a very nice combination, and I love playing outdoors just 'cause it sounds so good!
If you're playing a medium sized indoor venue like an auditorium or a theater, I've found that 15's are perfectly adequate. The things to watch out for there is resonances, 'cause a lot of large rooms have low frequency resonances that make 15's sound "boomy" and not at all pleasant. There are two ways to fix that: either EQ to compensate with a parametric, or use lots of really small speakers, or both. I usually use the EQ method, it works most of the time, but once or twice it hasn't worked and the gig didn't go well. So I always try to check out this kind of situation ahead of time if possible, usually I can tell just by yelling a few words in the room, what it's going to sound like and what equipment I should bring. 12's sometimes work well in this situation, they work especially well if you can get away with a fat midrangey tone at a lower volume, 'cause the extreme lows don't make it out into the audience with 12's.
If you're in a small club, you can get away with using 10's. That's my opinion. I wouldn't use them anywhere else, unless I had a whole bunch of 'em, and unless they were only for the high end. I detest 10's for several reasons. One is, I play a 5-string, and there aren't many 10's that can take the punishment of 31 Hz at a thousand watts. I've seen more than one 10" speaker cone flying all the way across the stage (and I mean "all" the way, like twenty or thirty feet), and all it took was one good whack on the low B. The other reason I don't like 10's is that if they're the only thing I'm using, then for my particular sound, they're almost "too" dynamic. I WANT some sluggishness and some fatness in my sound, that's what gives my bottom end the thickness and texture that makes it rich and intricate, and it allows the high frequencies to complement the sound in many ways that can't be achieved if the bottom end is "too" dynamic.
Edit: Oh yeah, forgot to mention, I prefer 15's for a small club situation, or more specifically one 15 and one 12 in parallel. I have a couple of EVX-155's that I use with Bag End 12's, I stack 'em in pairs for all but the outdoor gigs, that's where I substitute the big 18's for the 15's, so it becomes an 18 and 12 stack. That's my approach. I never use 10's. It's always either one 15 and one 12, or one 18 and one 12, I pair 'em like that. That gives me the sound I want just about anywhere. (End Edit)
So, there's my 2c worth. Happy New Year!
