While in-ear monitoring systems (IEM) are becoming more affordable, not to mention the fact that they offer a much cleaner mix than stage monitors, there are some risks to consider in terms of hearing damage due to high sound pressure levels (SPLs) being sent directly to the ears. These are the same concerns most recently brought to light with long-term use of iPods and other personal MP3 players with the volume set too high. And keep in mind that in-ear stage monitoring is capable of producing a much louder peak transient than any iPod.
So what’s the solution? Insert a compressor/limiter in line, with the limiter being set to extreme settings, referred to as brick-wall limiting. Basically, the limiter’s threshold control should be set well below the level at which ear damage can occur (generally around 110-120dB). The ratio should also be set fairly high, roughly 20:1 or even infinity:1 if your limiter allows for it. It’s also important that a very fast attack time is set, because it’s generally the peak transients that can cause the most damage.