Welcome to Andy Wilson's live sound engineering site.
As a sound engineer, my first audience, the one I most want to hear what they want to hear, is the band. They must hear each other in order to play well together. I put a great deal of effort and attention into getting the monitor mix right on stage, and that requires lots of interaction with the band during the sound check and sometimes into the first several tunes. Sometimes satisfying the band's need to hear each other and themselves requires multiple monitor mixes, though this tends to be more important with larger ensembles, particularly when they play instruments with very different intrinsic loudness (e.g., mandolin and accordion).
My second audience includes the people who are attending the event. I want everyone to hear each instrument on stage loud enough to be interesting and exciting, without making the music so loud that anyone's hearing is endangered. Another expression of my concern for people's hearing is my insistence that speakers should be placed as high above the floor as practical. Because sound is directed from speakers in somewhat the same way light is directed from a flashlight, this means that the loudest sounds are directed over the heads of the people directly in front of the speakers towards people in the back of the hall without being too loud for the people near the speakers.
One of the key considerations with live sound reinforcement is that the sound engineer is reinforcing the acoustic sound coming directly from the instruments to the audience. This means that instruments that are inherently loud, like piano, trumpet, accordion, or some percussion, needs less amplification than inherently quiet instruments like flute, or mandolin. Quieter instruments must be amplified enough to be heard against the direct acoustic sound from louder instruments. This is true in both the monitor mix and in the front of house mix that the audience hears.
I often run live sound for contra dances, where the caller's voice must be heard above the band. However, since the caller doesn't speak all the time, we don't want to have the band always set at a low level. When the caller is not speaking, the music should be loud enough to be fun and exciting for the dancers. Before a dance begins, the caller usually teaches the dance sequence to the dancers without any music playing. We don't want to caller to be too loud in the hall when there is no music playing either. All these competing demands on relative and absolute volume lead me to one of my signature contradance sound techniques: band ducking. This is a technique by which the band can be made comfortably loud without risk of overshadowing the caller's voice when he or she speaks, also without making the caller's voice painfully loud between tunes. The trick is to automatically and imperceptibly lower the volume of the band when the caller speaks, so the caller can be heard through the band without having to make the caller too loud. This can be done using a compressor that has a side-chain input. If you want to know more about this, write me to ask about it.
Probably the best little booklet I can recommend for the novice sound engineer is Bob Mills little booklet, All Mixed Up, which is available from the Country Dance and Song Society for $5 plus shipping. I highly recommend having this book in your kit as a quick reference while you're getting comfortable with your gear. There is a wealth of other material available if you're willing to wade through all the technical details. First on my list of recommended reading: the manual that came with the equipment that you use. Especially get familiar with the signal routing possibilities in your mixer. Find out what signal levels different parts of your equipment expect (and can tolerate) on their inputs and produce at their outputs. This is key to avoiding signal clipping and the resulting distortion of your signal and risk of damage to your high-frequency driver on your speakers. Next in line of favorite reading material is the Yamaha classic, Sound Reinforcement Handbook by Davis and Jones, and then perhaps Live Sound Reinforcement by Stark. Join the contra sound forum, a moderated, relatively low-traffic e-mail list where you can learn from lots of people who run sound in other places.
If you're interested in finding out more about the sound reinforcement that I can do for your event, feel free to write me to inquire. Thanks for your interest! I look forward to hearing from you.