Guide to getting and playing better gigs
Powered Monitors
It's hard to believe, but back in the so-called heyday of rock n' roll, it was rare for a semi-pro band to use any form of foldback. Today, it's not uncommon to find bands with more foldback watts than many old-timers had in their entire PA including backline.
The basic idea of foldback is that it sometimes (though not always!) helps if you can hear the balls-ups you're creating, and even those that your fellow musos are improvising. Vocalists are the most obvious candidates, because they often can't hear a word they're screaming against the competition from backline and drums. But then, the drummer wants to hear the bassist (whose backline probably isn't loud enough to cut through the racket the drums are making). And so it goes on. Even a fairly modest band may have a total of 700-800 watts between backline, PA and drums, so you need a fair portion of foldback power to cut through all the "ambient" noise.
Looked at like this, monitors with typical power ratings of 60-100 watts are by no means over-powered, although the actual loudness you can get is helped by the fact that you'll be a lot closer to the foldback than all the other sounds around you (unless you're the drummer). It's also helped by the distinctly mid-bright tonal balance that most designers go for - this can be tiring, but it does ensure an "in yer face and down yer gob" presentation.
Most powered monitors have some type of EQ, but it's generally pointless to use this to increase bass output - all that happens is that you waste amp power and increase distortion. Manufacturers often claim that their graphic EQs can help fix feedback, but the frequency range that each graphic band covers is so broad that it screws up the overall sound. The best answer is to use a 31-band graphic or a dedicated feedback "eliminator", but the cheap solution is to move the offending monitor or the mike that's causing the feedback.
Most monitors have a socket to add an unpowered extension speaker. Because of the way they're wired, this increases amp power, so a 100-watt monitor will deliver around 150-watts when used with a second speaker. Using two speakers makes sense for vocalists who move about a lot (and how many don't?).
Most people will be happy with the basic floor-mounting that wedge monitors provide, but some models offer extra possibilities: a more-nearly vertical front panel allows you to have the monitors further away, while vertical mounting on stands, will be useful for general PA "side-fill" monitoring.
See also: In-Ear Monitors