This is a common problem. Your mix from the front-of-house speakers sounds fine in itself, but the sound bouncing back from the monitors on stage is making everything sound pretty dreadful for the audience.
Some people will say that the answer is to use in-ear monitors. For a sound engineer to manage in-ear monitors for a band they work with regularly isn't too much of a problem.
For a venue's engineer to manage in-ear monitors for any group of musicians that turns up is another matter entirely and this would not be our general recommendation.
The advantage of in-ear monitoring is that none of the monitor sound gets back to front-of-house.
Why is that?
Because the monitors are now very close to the ear and produce hardly any sound output. Conventional monitors are much further away at floor level.
So if you consider these facts, the question almost answers itself.
The closer you get the monitors to a performer's ears, the less loud they need be and the less trouble they will cause for front-of-house.
In truth you don't need huge monitors on the floor. Better results will be obtained through smaller monitors mounted on stands closer to the performers.
This might be more visually intrusive. But this is no more wrong than a performer having their ears blocked up, and being sonically isolated from the response of the audience.
Another tip - monitoring is easier in larger venues, and in less reverberant venues. So a monitor engineer working in a stadium has a much easier time than someone working, say, in a small stone-interiored church.Come on the FREE COURSE TOUR