Distortion issue with wired IEMs attached to a long extension cable

[robussc]

I've joined a band where we're rehearsing at someone's house and using headphones (the drummer has an electronic kit thankfully). It's been going great and it's so nice to sing with a clean mix in my ears. We're all using standard studio headphones and it's all been working great. I've suggested that if we ever venture out onto a real stage we could switch out the studio phones for IEMs and still get the clean mix we've been enjoying.

I had a chance to experiment with that at the last practice when one of the guys forgot his headphones so I lent him mine while I wore my IEMs. But as soon as I put them in the mix sounded absolutely terrible. There was tons of distortion and almost a heavy reverb type effect on the overall mix.

I fiddled with things, but the only thing that fixed it was removing the extension cable and plugging the IEMs directly into the headphone amp.

I think I've read about this when I first exploring IEMs for live shows, but I can't seem to find it again via Google, but I'm sure one of the studio gurus here will know what I'm talking about and explain what's happening and what can be done about it? Impedance mismatch or not enough power or too much power or something?

In short,, regular studio headphones on the extension cable sound great. Wired IEMs on the same cable sound terrible. (These cables are 20ft long if that makes a difference?)

[jam-s]

Impedance mismatch sounds like a likely cause. Keep in mind that long wires have a higher capacitance and thus can alter the sound in case of low voltage signals.

[robussc]

Impedance mismatch sounds like a likely cause. Keep in mind that long wires have a higher capacitance and thus can alter the sound in case of low voltage signals.

I guess they're probably designed for wireless (and I do have one), but I've seen plenty of folks talking about wired systems so they must work somehow. Probably need some fancy wire in the cable: oxygen free copper and pure gold connectors!

[selig]

Don’t know about the distorted part, but the reverb part indicates a possible wiring issue canceling the center, something that can happen when you don’t plug all the way in or when using a cheap headphone extension (giving an imperfect fit).

Not sure how you’re connecting to the cable, but if you have a different connector going from 1/8” to 1/4” it could work better. Or a better extension cable maybe? I moved away from the fully molded to a more robust metal connector for my studio HP extension cables and haven’t had these issues for years now.

[robussc]

Don’t know about the distorted part, but the reverb part indicates a possible wiring issue canceling the center, something that can happen when you don’t plug all the way in or when using a cheap headphone extension (giving an imperfect fit).

Not sure how you’re connecting to the cable, but if you have a different connector going from 1/8” to 1/4” it could work better. Or a better extension cable maybe? I moved away from the fully molded to a more robust metal connector for my studio HP extension cables and haven’t had these issues for years now.

That's interesting. Certainly the connection is a tight fit, but I did think I double checked that, but now I will again. Thanks!

These cables are quite nice, 1/4" stereo to 1/8" stereo so it would be great if they worked!

[robussc]

Impedance mismatch sounds like a likely cause. Keep in mind that long wires have a higher capacitance and thus can alter the sound in case of low voltage signals.

I checked the PreSonus HP 4 manual and the IEM manual and it does look there's a mismatch, the PreSonus headphone outs have a working impedance of:

Headphone Impedance Working Range 32Ω – 600Ω

While the Shure SE-215 Pros have an impedance of 20Ω

Is there a way to adjust that? I know there are plugs to increase impedance, but it seems unlikely that it can be lowered?!

[robussc]

Going to give this a whirl and see if it tricks it into working better:

https://a.co/d/3gsbn5h

[jam-s]

You can match the impedance using a small transformer with the right coil ratio. I've also found those impedance plugs here which might be of help.

EDIT: looks like you also found those

[DaveyG]

This sounds like a more fundamental problem than mismatched impedances.

[robussc]

This sounds like a more fundamental problem than mismatched impedances.

Perhaps, I definitely might not have it plugged in all the way. But the impedance is also pretty fundamental (especially when it’s going to wrong way! ) I didn’t realize how low these IEMs are!

[robussc]

EDIT: looks like you also found those

Yep thanks! Going to do another test this weekend (hopefully under less time pressure to get practice started than last week!)

[robussc]

You can match the impedance using a small transformer with the right coil ratio. I've also found those impedance plugs here which might be of help.

EDIT: looks like you also found those

Yep, that solved it! The impedance plug sorted it right out. Suddenly everything is coming up roses!