Or, I guess they don’t have to be custom fitted, so long as they provide adequate hearing protection. Ideally, an IEM + transmitter / receiver set that accommodates multiple users, protects hearing, and permits different mixes for each musician (in descending order of importance).
Mainly small-time gigs, bars and outdoor festivals, a variety of venue sizes and conditions, but nothing huge. For frame of reference, most of our gigs I play through a 15-watt tube amp, and it’s plenty loud. We cover classic rock tunes and we do NOT try to rattle the windows.
If you’re in a pinch, with no custom ear monitors at hand, take one square of toilet paper, and fold it in half.
Fold it in half again, so you’re left with a strip about a centimetre wide, and then just roll it up like a Swiss roll, and boom - in your ear it goes.
Excellent for cutting out the truly tinnitus-causing noises like cymbals, which I think are the worst. If the plug’s too big for your ear, just tear away a little bit until it does fit.
Did this every time I stepped behind my kit for the 23 years I was involved with super loud, abrasive, harsh noise, and my hearing is better, now, than actually most people I know. {{{Always}}} hearing frequencies others don’t. ('tis true, Kenneth.)