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Q. What’s causing distortion in my in-ear monitors?

By Hugh Robjohns
Published January 2021

If the amp for your in‑ear monitors is distorting, chances are it’s simply that it’s being fed too hot a level from the mixer!If the amp for your in‑ear monitors is distorting, chances are it’s simply that it’s being fed too hot a level from the mixer!

My church is using Shure SE‑215CL in‑ear monitoring with PreSonus HP2 personal amplifiers, and the sound is distorted at higher volumes. I have checked the gain staging but I’m thinking the headphones and amp aren’t a good combo. Please tell me if the headphones and amp we have should work together — and if not what amp or what headphones we should get to fix the issue. I’ve been trying to figure it out but it’s so confusing!

SOS Forum Post

SOS Technical Editor Hugh Robjohns: I suspect the problem here is not your choice of amp and headphones, but of gain structuring. The specs for the HP2 are confusing, in that they use random amplitude references in quoting a maximum input level of +4dBV and an input limit of +5dBm. But the bottom line is that the maximum input level to the HP2 appears to be around +5dBu, which isn’t a lot when most consoles will be able to put out +20dBu or more. So getting the gain structuring right from your console will be critically important to avoid overloading the amp inputs. On an analogue desk, you’d need to keep the sends below 0VU, and on a digital desk, below ‑20dBFS.

As for IEM/amp compatibility, the HP2’s output power is quoted as 50mW per channel with a 20Ω load. That’s fine, as your Shures are close to that at 17Ω, which is also comfortably above the 12Ω minimum impedance specified for the amp. The sensitivity of the SE‑215CL is pretty high at 107dB/mW, which means the HP2 amp should be able to generate around 123dB SPL into the performers’ ears. That ought to be more than loud enough, seeing as it’s the nominal threshold of pain! If users are complaining that they’re not loud enough, it might be worthwhile checking their earpieces for wax blockages, and to ensure they’re fitting the earpieces correctly.

Published January 2021