Re: PA question... powered mixer vs unpowered mixer + power amp?
Another board I'm considering. A question about something on that board as well, why are the last 4 xlr inputs listed with 2 channels each?
I have this exact board, and I love it. (I can truly say that Yamaha has *never* let me down with any piece of equipment or instrument.)
To answer your question, the two channels per strip is a common trick that you will see on these compact boards for fitting more mixer channels into a smaller space. The rightmost four mixer strips (in this case) can be used to mix either mono or stereo signals. So you can plug a Left and Right cable into these channels, and you will get slightly different controls than you would for a mono signal. For example, a mono signal has a Pan knob to place it in the Left-Right sound field; in a stereo track this will act as a Balance control that adjusts the relative volume of the Left and Right signals. The slider on those channels adjusts both L+R levels together. You would usually use the stereo channels to mix a keyboard, drum machine, or output from a stereo guitar processor.
You cannot easily use stereo mixer channels independently, so it is best to think of this board as only able to mix 16 different sources, even though it has 20 audio channels in the main mixer section. Stereo strips are convenient for stereo sources, as you don't need to move two volume sliders together at the same time to affect the instrument level. You can also use one half of a stereo strip as if it was a mono section, but it is not so easy to run two different sources through the L+R sides of a stereo strip.
Things I like about this particular mixing board are: The onboard compression - very handy for vocal mics and even Bass. The EQ is very good on this board as well. And it is nice to have a 20-channel mixer in a rack-mount space. Decent pre-amps, too.
The only thing I don't like about this mixer is that the input jacks along the rear/top of the board do not line up with the mixer tracks below. (A side-effect of trying to cram all those strips into one rack width.) This can be confusing, because I am used to finding the right strip by following the cable downward. Just yesterday I was looking at this board and deciding I need to add some slanted guide lines to visually reinforce which inputs go to which strips.
As far as mixing for monitor feeds, you want to be aware of the number of mixing busses at your disposal. Mixers are often described using a string of three numbers to describe the number of parallel audio paths at each stage. The Yamaha board you are looking at is a 20 x 4 x 2 mixer, for example. This means that it can take in 20 audio signals and mix them into 4 independent "Aux" signals that can then be mixed down onto your 2 main stereo out signals. (You can also mix each of the 20 inputs to the Main outputs directly.) You can use the four "Aux" knobs in each mixer strip to set the level of each instrument independently in each of the four Aux mixes. These are commonly used to create monitor mixes, so you could have four different monitor mixes on stage without impacting your ability to set the house mix. Aux busses add size and cost to a board, so best to figure out how many you can live with - 2 or 4 Aux busses is common on boards this size.
One other thing to keep in mind is that when you are recording you will usually mix in stereo, but when playing live, you will probably run a mono bi-amped setup. You want people in the live audience to hear the same thing no matter where they are sitting, so usually your Left and Right speakers will be playing the same audio. Because you still have L+R Main outputs, many bands will EQ these differently to run one side to the regular speakers and the other to either your horns or your subs. This lets you send bass and kick drum mostly to one set of speakers to avoid saturating the amp that is also carrying vocals and melodic instruments. The point being, you will probably mix differently when live vs. recording, but the same equipment should handle both situations.
Not to beat the Yamaha drum too much, but I recommend you read the Sound Reinforcement Handbook. (You can
download a free PDF file if you don't want to spring for the actual book.) There is a ton of great information in there about every facet of running a sound system. I refer to this book often.
