The IEM (in ear monitors) Bible thread - a guide to help every musician

[TimR]

I don't think your brain would notice ears being out of phase as that happens all the time with sounds arriving at one ear before the other. 

[Al Krow]

16 hours ago, TimR said:

I don't think your brain would notice ears being out of phase as that happens all the time with sounds arriving at one ear before the other. 

 

Thanks Tim. Makes sense! 

 

On 10/01/2026 at 17:31, TimR said:

Page 69.

Alt Out (CQ-20B)

The Alt Out provides an alternative balanced TRS output connection. Source – Select any other Output or route the Listen out.

 If Listen is set, when no Listen button is pressed, the Alt Out will be sourced from Main LR.

 Listen is sent to the Alt Out at full volume for use with IEM systems that have input level control. For adjustable level, the headphone output should be used. 

 

I've had at a look at the manual reference and the two Alt Out sockets are for the CQ-20B model only (not present on my model the CQ-18T). "Listen mode" simply changes the mix to be some as FoH (ie sourced from Main LR). It won't change the nature of the Alt out from being balanced TRS to stereo TRS though, which is the point we seem to have moved on to. Although the manual is does seem to imply that using balanced TRS with IEM systems is fine.

 

If it makes an "in principle" difference, I guess it would be best practice to be using the silver TS to TRS adapters as standard rather than the gold TRS to TRS adapters (per pic at bottom of previous page)? And this is a more general point?

 

Those plugging their 1/4" stereo jacks from their wireless IEMs (eg Swiff WX520) into a single balanced mono aux-out jack will just have to take what they get!

 

@Woodinblack be good to get your trained electrical engineering hat on this!

 

Edited 3 hours ago by Al Krow

[Woodinblack]

14 hours ago, TimR said:

I don't think your brain would notice ears being out of phase as that happens all the time with sounds arriving at one ear before the other. 

 

It would be exactly the same as the sound coming entirely from one side, ie 90° to you, but somehow being as loud on the back side

 

 

14 hours ago, Al Krow said:

If it makes an "in principle" difference, I guess it would be best practice to be using the silver TS to TRS adapters as standard rather than the gold TRS to TRS adapters? 

 

What is a TRS to TRS adapter? Why would you need to adapt that?

 

14 hours ago, Al Krow said:

Those plugging their 1/4" stereo jacks from their wireless IEMs (eg Swiff WX520) into a single balanced mono aux-out jack will just have to take what they get!

 

if you plug a mono lead in, it would be fine, its only with a stereo lead. Thats one advantage of a balanced output, it would give you a fine mono output if you use a TS jack.

[SimonK]

Was procrastinating and wondering about the difference between dBu and dBV was this morning. The following article is really interesting and especially the table at the end that touches on an issue that comes up time and again in amp threads.

 

https://www.soundonsound.com/sound-advice/decibels-explained

 

[Al Krow]

1 hour ago, Woodinblack said:

It would be exactly the same as the sound coming entirely from one side, ie 90° to you, but somehow being as loud on the back side

What is a TRS to TRS adapter? Why would you need to adapt that?

if you plug a mono lead in, it would be fine, its only with a stereo lead. Thats one advantage of a balanced output, it would give you a fine mono output if you use a TS jack.

 

Thanks Woody - the TRS to TRS is simply a 1/4" to 3.5mm TRS adaptor - please see the pic in my last but one post (bottom of previous thread page). Seems to make no difference using that vs using a TS a TRS adaptor - but that may just be us not being overly impacted by the phase issue?

 

I think what you're saying is best practice would be to use the TS to TRS adaptor (the silver one in the same pic)?

 

And what this discussion has also made me realise is that if we want to transition to getting stereo for our IEMs e.g. with the Swiff WX520 - the A&H CQ-18T has two stereo headphone outs that could be assigned to providing this for two members of the band. We then have a further 6 balanced mono outs, some of which can be paired to provide additional stereo IEM feeds for those that want it (obviously not an option for the Xvive U4 users). That's definitely an additional worthwhile take-away from this chat! 

 

Edited 3 hours ago by Al Krow

[MichaelDean]

There has been some talk in my band of potentially investing in an IEM setup with an XR18. What's the best way of combining the two XLR outputs to one TRS jack cable?

[dave_bass5]

37 minutes ago, MichaelDean said:

There has been some talk in my band of potentially investing in an IEM setup with an XR18. What's the best way of combining the two XLR outputs to one TRS jack cable?

I have one of those cables that i occasionally run in to a P2. You could also use the headphone out with just a standard stereo jack cable.

Edited 4 hours ago by dave_bass5

[Woodinblack]

1 hour ago, Al Krow said:

I think what you're saying is best practice would be to use the TS to TRS adaptor (the silver one in the same pic)?

 

Yes.

 

1 hour ago, Al Krow said:

. We then have a further 6 balanced mono outs, some of which can be paired to provide additional stereo IEM feeds for those that want it (obviously not an option for the Xvive U4 users). That's definitely an additional worthwhile take-away from this chat! 

 

 

indeed - that's what mine are (as I have balanced TRS outs on the X18)

 

 

For normal mono outs, I have TRS to XLR adapters, and I do have a dual XLR mono to XLR stereo cable (or a few of them) that I could use, they usually are with the chapman stick that has a stereo out. 

 

- edit - I note that this is now actually OTT, as I could go from the stereo ¼" jack to the ¼" jack on the IEMs - its just I have these cables anyway as I was using the MS-2 before hand, and that only had a 3.5mm jack

[Phil Starr]

15 hours ago, Al Krow said:

 

Hmmm...

 

We've got balanced mono aux outputs as previously noted.

 

We've got and used a 1/4" TS to 3.5mm TRS adapter jacks (the lower silver jack in pic) to allow us to plug in to the desk to deal with the issues that Woody mentioned.

 

What stumps me though is why we're getting equally good results with 1/4" TRS to 3.5mm TRS stereo adapters (upper jack), with standard IEM headphones with standard 3.5mm TRS jacks?! So we're using either without issue.

 

 

 

My coffee time teaser for today   (mainly because I'm not 'allowed' to do Wordle)

 

So the first thing to understand is that balanced line signals have an earth that is at 0V and two other signals +ve and -ve. The two signals go up and down at the same time but when + is going up - is going down. When the signal gets to the amp a transformer or a bit of electronics turns this back to an unbalanced signal.

 

In a jack the tip should be +ve and the sleeve is the earth the ring should be -ve and inside the jack socket there are three sprung contacts that touch the plug when it is connected. Many jack sockets also have switches built in operated whenever a plug is inserted, so this can complicate the wiring. If you use the mono jack (the bottom one) then the - and the earth connectors in the socket are both touching the sleeve and are short circuited. What happens next depends upon the grounding arrangements. Since it is working for you then there are no issues. It doesn't work on my Flow 8 for example unless I only insert the plug halfway.

[Al Krow]

3 hours ago, Woodinblack said:

 

Yes.

 

 

indeed - that's what mine are (as I have balanced TRS outs on the X18)

 

 

For normal mono outs, I have TRS to XLR adapters, and I do have a dual XLR mono to XLR stereo cable (or a few of them) that I could use, they usually are with the chapman stick that has a stereo out. 

 

- edit - I note that this is now actually OTT, as I could go from the stereo ¼" jack to the ¼" jack on the IEMs - its just I have these cables anyway as I was using the MS-2 before hand, and that only had a 3.5mm jack

 

Thanks Woody. Amusingly I have the exact same red-white dual TS -> single stereo TRS jack adaptor, which I use to feed Spotify tracks to the desk from my PC at home (or phone at a gig between sets), into the stereo input of the CQ-18T. Makes sense that you can use the exact same bit of kit to combine two balanced mono aux outs -> stereo jack of your IEM. Obviously plugging directly in a single stereo TRS headphone out achieves the same thing and we are fortunate to have two of those on the CQ-18T.

 

I've actually got a couple of those silver 1/4" -> 3.5mm TRS jacks (in my pic on the previous page of this thread) and will make those the default for us where we are using single Aux-Out balanced mono -> stereo TRS IEM jack.

(In fact, just ordered an extra few spares, because they don't last forever! In case useful for anyone else - you can get 3 from Kenable for under £4 inc. P&P)

 

As @Phil Starr has rightly pointed out, and which completely ties in with my own experience from a full year of gigging with the A&H CQ18T, many desk aux-outs should easily be able to provide enough output for headphone users to directly plug into the desk and hear themselves clearly and easily. If yours doesn't, you may need the assistance of a headphone amp (like the Behringer P2). But best practice when plugging a stereo IEM jack directly into an Aux balanced-out, to avoid phasing and other issues, is to use one of those Kenable-type TS -> TRS convertors.

 

Right I think that's me sorted! Really appreciate, as ever, the BC collective-wisdom on this and I now understand a bit better why our current setup has been working so well, particularly when old rules applying to older tech might caution against! Back to the fretboard...

 

Edited 13 minutes ago by Al Krow

[Muzz]

On 08/01/2026 at 09:41, Woodinblack said:

 

I have never actually ever had a problem with the MS-02, just they feel a bit flakey, and on mine the power button is not the best (it works, but its like if you push it too much it goes off again). I think they are a great system for the price (wish the stereo / mono and on/off buttons were further apart!) and I will keep them as a backup

 

 

My channels aren't linked, I never got round to it, I just use 5 and 6 as a pair, and set them manually as I want them. 

 

On 08/01/2026 at 10:19, dave_bass5 said:

Can you not do it yourself in whatever app you are using, or do you mean he doesn’t want it done?

The drummer and I are locked out of everything but our individual Aux channels on the mixer app...it's his mixer, y'see...

[Muzz]

On 08/01/2026 at 12:26, Al Krow said:

 

That's a very tidy haul, Muzz - congrats! (And hopefully you're not about to tell me that bookings were down 40% and it was actually a really crap year for you guys!)

 

Are you guys doing a mixture of pub and function work or predominantly doing one or the other?

Pubs, pubs, pubs...the odd beer festival (I think a couple last year), but yeah...pubs...