What about monitors?

Why do you need them?

When you are on stage, unless you are playing at the lowest levels, it is almost impossible to hear your vocals coming out of the main PA speakers or get an overall impression of how they sit in the mix from an audience perspective. The consequence of this is that you will tend to over-compensate and sing louder and ultimately start shouting!

The problem gets worse if you are putting a keyboard or electric guitar directly through the PA.

Monitors should not really be used for your back-line instruments. You should be able to adjust your on-stage volumes if you can't hear properly.
 

How do they work?

• Monitors take a separate output from your mixer (either Monitor Out or you can use an Effect Send)
   

• Each channel on your mixer will have a knob to control how much of that channels signal is passed to the Monitor Out. This means that you can control the balance in the monitors between different microphones or instruments.
   

• The Monitor Out from the mixer is connected to either a separate monitor amplifier with passive speakers or directly to powered (active) monitor speakers.

Should I get passive or active (powered) monitor speakers?

Other considerations

We don't have a Monitor Out or Effect Send on our mixer!
You can use the main mixer output (use a splitter if you only have one main out). But, this will put the whole mix through the monitors and you will not be able to control individual levels. This may not be a problem. If it is, upgrade your mixer.

Reverb in my monitor?
Unless you have a sophisticated mixer with separate effect sends for the monitor mix, the monitors will not have reverb or any other effects applied to them. (You could put the monitor out through a separate reverb unit to add reverb to the monitors).

What size monitors?
If you are only using the monitors for vocals or acoustic guitar, then 10 inch speakers should be fine. Otherwise go for 12 inch. In terms of wattage then 80W to 200W should be ample.