Yo Ironside! Let's start simple, because like a Japanese owner's manual, these guys are assuming you know stuff that you don't. A speaker out and a line out are 2 whole different animals. Basically, a system for live sound reinforcement consists of a preamp section, a power amp section, and one or more speakers. This system could be a guitar amp, which is designed to
change the sound being inputted, hopefully to make it sound better, or a clean power amp, designed to make the signal from the preamp more powerful, without changing it too much. PA systems tend to be the second type. Of course, some guitar amps, especially acoustic guitar amps and some bass amps are pretty damned clean.
The power amp can be in the mixer or PA head, in the speaker enclosure, or a completely separate unit. If the power amp is in the speaker enclosure, it is called an "active" or "powered" speaker. So- for a PA, you can use a nonpowered mixer into an active speaker, a powered mixer into a passive speaker, or the mixer, the power amp, and the speaker can be 3 separate units altogether.
Many live speaker systems use crossovers, so that low frequencies are sent to speakers built for that (woofers) and high frequencies are sent to speakers built for that (tweeters). There are likely to be specific speakers for midrange frequencies as well. If a speaker enclosure has a woofer and a tweeter, they call it a "2 way" speaker. If there is also a midrange speaker(s), it is called "3 way". As with power amps, the crossover can also be a separate unit, usually rack mounted. A speaker/cab built specifically for very low frequencies is called a subwoofer. Because low frequencies have very long wavelengths, they are not really directional. Therefore, a system may have 2 2-way or 3-way enclosures, or 2 main speaker arrays and a single subwoofer in the middle. Massive systems may have a number of dedicated speaker cabs, and the multichannel crossover from hell.
Monitors, like main speakers, can be active, or passive. They are smaller speakers, usually on the stage facing you, so that you can hear yourself and the other members of the band. In some cases, the monitor is in your ear, like a hearing aid, and is wireless. Some drummers prefer headphones to monitors, because they attenuate (cut down) the drums around them, so they can hear the other band members. Advanced systems can send customized monitor mixes to the different members of the band, so each of them can hear what they need to. Obviously, as the size and complexity of the system increases, the more it costs, the more gear you have to move, and the more engineering you will need for the setup and performance. Some small bands that do small gigs don't even use monitors.
An active speaker (with a power amp in it) is looking for a line level signal, which is what comes from a preamp. A preamp is designed to raise the relatively weak signal of a mic to line level, so that it can drive a power amp, which will then drive a speaker cab. Mixers are basically a bunch of preamps with separate controls, and a variety of options for configuring those outputs. A preamp that is designed for an instrument input like a guitar, is called a direct box or DI (direct injection) for short. Instrument inputs are looking for higher impedence than most mics. This is called an instrument, high impedence, or high-z input. Some mixers have high-z inputs, but many don't. Note that some mics, especially older ones, or specialty mics, like harmonica mics, sometimes are looking for a high-z input, rather than a "mic" input. Most modern stage mics are low impedence, and are looking for a "mic" input. In most modern systems, the mic inputs will be 3-pin XLR connectors, and most line and high-z inputs are 1/4", like a guitar cable. Some guitar and bass amps have line level outputs, which are OK to plug into a line level input on a mixer, PA head, power amp, or active speaker. Many amps *don't have* a line level out. That's why folks are telling you not to plug a guitar amp into a mixer or PA. They are afraid you will plug the speaker output (post-power amp) into a mixer preamp, and blow it to kingdom come. Doing that is like firing a bazooka at a dartboard.
In recent times, there have become available specialized guitar preamps, which characteristically use digital amp modeling technology to try and copy the sound of a bunch of different amps. They can be plugged directly into a line level input on a recording device, or into a PA. High end- Pod XRT. Cheap-
Behringer Vamp2. Most guitarists would agree that amp modeling preamps are still inferior to the sound of a good amp. Problem- the line out on an amp plugged into a PA usually does not sound as good as the specially chosen preamp/poweramp/speaker cab combination that the amp uses to get that killer sound. Common solution- put a mic in front of the amp and send that to a mic input on the PA.
How much power you need in a PA depends on the type of music, the size of the crowd/hall, and how big your amps are in the fiirst place. If you are playing a gig with 50 people and you have a 400 watt Marshall stack, please don't mic it up! You may very well need to turn it down to hear the drummer.
If you are playing Shea stadium with a Vox AC30, it will have to be mic'd up.
The more stuff you intend to run through the PA, the more power you need. If you play very loud Death Metal, you will need 2 to 3 times the power that James Taylor would need in the same hall. If the gig gets over medium-sized small, it will become necessary to put mics on the drummer, who will need a minimum of 4 channels, and possibly 8 or even more for hard rock/metal.
The only thing that is pretty much guaranteed to go through the PA is vocals. Almost all PA's of any type will have a built in reverb unit. Reverb is almost always used on vocals, and almost all PA's will have some EQ, for tweaking sound and dialing down feedback frequencies. As far as power, most smalltime bands get by with 600-1200 watts, depending on how much stuff goes into the board (PA), the type of music, and the size of the halls they play. Although I have played in a number of bands, now I am a solo folkie, and I get by fine with 250 watts. BTW, for what I do, switching back and forth between acoustic and electric, I find an amp modeler plugged into my little PA does exactly what I need it to do. A big-club Death Metal band will feel somehow deprived with less than 5000 watts and the required 15-20 speaker enclosures. Each to their own. BTW, the system recommended above is a perfectly good place to start. Hope this helps.- Richie
the biggest confusion i have is how do you avoid blowing out your speakers? i'll have a bassist and a two guitarists plugging into the mixer at any given time, along with a mic. How do you buy speakers that won't blow out? where do you look to see how much the speaker can handle, and how much your amp outputs, that sort of thing. Also: I've been told that there's no power in mics, so if we just plug in a singers mic, and mic the rest of the instruments amps, theres no danger of blowing out the speakers right? the only danger is if we connected the amps straight to the mixer? We'll be playing in churches, coffea houses, maybe a school gym, nothing huge. Can you give me an idea of how many watts or OHM's or whatever I will need? i'm sure you experienced people are groaning and rolling your eyes, but any help would be appreciated. It seems like no one can give me a straight answer on how to keep from blowing out your speakers, and how large a speaker you'll need. I say again, if you can answer any (or all) of the questions in this post, i'd really appreciate it.
