2-Channels On 1-XLR Cable?

[SurferJoe46]

I bought this mixer board::

.....and I have two mics with only one shielded cable that are in the same physical location when used and those mics need to be brought to the mixer.

The problem is that there's a permanently installed single XLR jack/cable in the wall - stage right, far end - all boarded/sealed up and runs for 40-feet inside the studs to the mixer station.

Ripping the walls apart and running new cable is out of the question here. And this must stay a hard-wired setup according to the facility/owner.

I wonder if I can send both mic signals down that single XLR-shielded cable to the mixer and split it back into a stereo channel and just use a stereo/balanced input to the board?

I'm thinking of using CHANNEL 7/8 for this, but don't want to cause any troubles to the ground of the board in case I am going to be shorting out the coax cable-to-the-mixer.

Using the shield as the return halves of the mics might give me a lot of noise potential - but I'd like to try it if it won't smoke the system.

I just want to make sure the board is gonna be OK with this experiment.

 

[TL5]

What are you mic'ing?

Curious;
I understand you want the mixer/FOH position to get both mics independently.
Is there a reason why you're dismissing the idea of putting mic one in channel 1 and panning it left, putting mic 2 in channel 2 and also panning it left, then sending the left side only to the FOH/mixer?
That'd put the blend in your hands instead of FOH, but it'd still accomplish the same end result.

 

[MNAirHead]

you have stereo sends.. use TRS or 2 1/4 plugs.

 

[SurferJoe46]

What are you mic'ing?

Curious;
I understand you want the mixer/FOH position to get both mics independently.
Is there a reason why you're dismissing the idea of putting mic one in channel 1 and panning it left, putting mic 2 in channel 2 and also panning it left, then sending the left side only to the FOH/mixer?
That'd put the blend in your hands instead of FOH, but it'd still accomplish the same end result.

I have channels 1, 2, 3/4, 5/6 already in use and just need to get 2 mics through the walls for 40 feet to the mixer. I am trying to use just what's there now and not have to tear into a wall to run a second XLR coax cable.

This situation is a lecture hall, and there's a moderator's dais, a stage left single boom and the dual mics on the stage right side and dual wireless rover mics for the audience 'question & answer' interaction.

The two mics on the discussion/panel table can just be panned for individual VOL control as they will both be hot at the same time anyway - so that's not a problem.

CHANNEL 1 = RIGHT AISLE AUDIENCE ROVER
CHANNEL 2 = LEFT AISLE AUDIENCE ROVER
CHANNEL 3/4 (as MONO) = DAIS
CHANNEL 5/6 (as MONO) = STAGE LEFT MIC ON BOOM
PROPOSED CHANNEL 7/8 = DUAL STAGE RIGHT TABLETOP PANEL~DISCUSSION MICS
​

Everything's up-n-running and working well, except for the discussion table, and that's still running on the old EQ/AMP pots.

I just need to send that dual-mic signal through a single shielded XLR cable if possible.

The reason for installing this mixer was to take the constant pot-twisting off the EQs on the amp and put it on something that's more made for constant changes and ON/OFF switching.

Originally they used the amp EQ pots for ON/OFF of the mics and then had to quickly adjust the VOL to keep from booming or being too quiet because of people having different mic-handling and voice volume.

The amp EQ pots were getting scratchy and making noise and this is what I came up with. Now there are silent switches that have very nicely circumvented that problem on the new board.

BTW: What's 'FOH' mean?

.

 

[KeithAlanK]

FOH = Front Of House = the audience (and mixing position)

To answer the OP: Wireless mics is the best answer, except for cost.

 

[SurferJoe46]

FOH = Front Of House = the audience (and mixing position)

To answer the OP: Wireless mics is the best answer, except for cost.

TY for the FOH partr.

They want to stay away from MORE wireless units as they don't like what they have now in the two wireless rovers and they are always getting hit by some guy 1/4 miles away with his megawatt CB rig.

I may have to do a subfloor or overhead crawl to run more coax I guess.

 

[jazzblade]

I guess you could try using the high level outputs from a small mixer on the stage. Split the in place Balanced line input to left/right common ground and sent that to the mixer if you have line level inputs available.. But 40 feet is pushing it.

Is that what your thinking??

I have run longer line level signals that 40 feet but never using the same cable for both left and right signals.

 

[Bofee]

Sub-mix with something like this:
http://pro-audio.musiciansfriend.com/product/Behringer-EURORACK-UB802-Mixer?sku=631238

Or if you want battery powered:
http://pro-audio.musiciansfriend.com/product/Behringer-XENYX-1002B-5Channel-Compact-Mixer?sku=582087

 

[jazzblade]

Sub-mix with something like this:
http://pro-audio.musiciansfriend.com/product/Behringer-EURORACK-UB802-Mixer?sku=631238

Or if you want battery powered:
http://pro-audio.musiciansfriend.com/product/Behringer-XENYX-1002B-5Channel-Compact-Mixer?sku=582087

Yes I was suggesting using a sub mixer but he still wants to send a STEREO feed to the amp. So to clarify, use a sub mixer or the mixer you have, (still confused about the current setup) take the two mikes into the mixer, send the line level out of the mixer down the current installed single XLR (adapting the cable ends for L/R common ground and send this into the amp or mixer so you would still have a stereo pair.

 

[SurferJoe46]

I guess you could try using the high level outputs from a small mixer on the stage. Split the in place Balanced line input to left/right common ground and sent that to the mixer if you have line level inputs available.. But 40 feet is pushing it.

Is that what your thinking??

I have run longer line level signals that 40 feet but never using the same cable for both left and right signals.

Yes I was suggesting using a sub mixer but he still wants to send a STEREO feed to the amp. So to clarify, use a sub mixer or the mixer you have, (still confused about the current setup) take the two mikes into the mixer, send the line level out of the mixer down the current installed single XLR (adapting the cable ends for L/R common ground and send this into the amp or mixer so you would still have a stereo pair.

UPDATE:::

I ran the system tonight for the first time with an audience and speaker and discussion table and all.

Everything but the discussion table was 100% satisfactory and worked great!

What I found out is that the discussion table has something very wrong in the wiring coming to the amp/mixer from the floor jacks-back to the old amp unit.

I couldn't test this until today and under actual use I found out that the coax cable is a dead short somewhere in the middle and I'm gonna have to run a new pair of cables from them to the board anyway.

For today we just ran the wireless rovers in desktop stands and let it go for now. But this Saturday I get to go in there and make the crawl through the ceiling - which I did NOT want to do - and then all will be up-n-running.

Still - just academically - I wonder if there wasn't a short in that coax, could I run two separate mics through that single XLR cable and just split it at the board and control it from there with the PAN pot on the 7/8 channel?

 

[JackANSI]

If you convert the balanced signal from each mic to unbalanced using a transformer you could do it. You'll definitely get a measurable (and definitely audible) amount of noise from two 40' unbalanced runs (especially if some guys "megawatt cb" rig is cutting in on your el'cheapo wireless units) and a remote possiblilty of crosstalk between the channels as well.

Not to mention the issue of mistrust you'll gain with the people you are doing this for if someone comes in and trashes your reputation for doing something so silly instead of just running more channels.

Just use the old run and some conduit lube to pull the new pair... Not hard.

 

[bruiser1964]

Why not save yourself the heartache and just tie 2 cables to the old one at one end and pull them through and fit new surface sockets?
Sparkies do this all the time without damaging walls.
Good luck!

 

[cavemusic]

UPDATE:::

I ran the system tonight for the first time with an audience and speaker and discussion table and all.

Everything but the discussion table was 100% satisfactory and worked great!

What I found out is that the discussion table has something very wrong in the wiring coming to the amp/mixer from the floor jacks-back to the old amp unit.

I couldn't test this until today and under actual use I found out that the coax cable is a dead short somewhere in the middle and I'm gonna have to run a new pair of cables from them to the board anyway.

For today we just ran the wireless rovers in desktop stands and let it go for now. But this Saturday I get to go in there and make the crawl through the ceiling - which I did NOT want to do - and then all will be up-n-running.

Still - just academically - I wonder if there wasn't a short in that coax, could I run two separate mics through that single XLR cable and just split it at the board and control it from there with the PAN pot on the 7/8 channel?

There are 3 connections in an XLR line. So I guess what you're suggesting is run one signal from each mike on 2 connections, and the mikes share the third ground connection. There are two problems with doing this. First, running unbalanced mic signals is definitely more likely to pick up electromagnetic interference (noise). Second, the inputs on 7/8 are line inputs. You'd need mike preamps for each mike anyway. So as others have mentioned, get a cheap two channel mixer with two mike inputs to use up by the stage - pan them left and right to get two line level signals out of that mixer. Two unbalanced line level signals over that 3-conductor XLR line might be okay running 40 ft. if that area is not polluted by noise, but it would still be more susceptible to noise than running balanced.

The proper, least likely to fail method is run more cable.

 

[T-Bird]

Hi.

What You're wanting to do isn't possible if money is tight or at least some signal S/N ratio is a concern.

Just use the old run and some conduit lube to pull the new pair... Not hard.

Why not save yourself the heartache and just tie 2 cables to the old one at one end and pull them through and fit new surface sockets?
Sparkies do this all the time without damaging walls.
Good luck!

^^These.

I would run a 3 or 4 pair multi pair cable there though, if 2 mic lines is what You require now, it'll be more in the future or someone wants a return feed to that location as well. Do use individually shielded pair cable though, the twisted communications cable will be asmost as bad as running both the signals unbalanced in one pair.

Regards
Sam

 

[SurferJoe46]

There are 3 connections in an XLR line. So I guess what you're suggesting is run one signal from each mike on 2 connections, and the mikes share the third ground connection. There are two problems with doing this. First, running unbalanced mic signals is definitely more likely to pick up electromagnetic interference (noise). Second, the inputs on 7/8 are line inputs. You'd need mike preamps for each mike anyway. So as others have mentioned, get a cheap two channel mixer with two mike inputs to use up by the stage - pan them left and right to get two line level signals out of that mixer. Two unbalanced line level signals over that 3-conductor XLR line might be okay running 40 ft. if that area is not polluted by noise, but it would still be more susceptible to noise than running balanced.

The proper, least likely to fail method is run more cable.

That's what I've discovered by trial and error - mostly error. Let's try a different way then - OK?

ABOUT ADDING AN ON-STAGE MIXER/VOL CONTROL:::

The two mics on the stage right cannot be controlled by the mic users and there's no place to put someone else to monitor their output.

The whole stage is only 8 feet deep and 22 feet wide and no place to hide anyone in a box or alcove either.

There is no 'back stage'.
There are no 'stage wings'.​

The people who would be at that discussion table are barely capable of using the mics, let alone any panning or mixing controls at the same time - it would be out of their experience and league. These persons change every 20 minutes or so and rotate every week. There's no time for an AV 101 class to teach them.

That particular table is for discussions and they usually take turns talking (if all goes well). I will obviously have to control their mics from the amp/mixer area and that's about 40 feet away at the control panel.

I intend to do that with twin mics feeding the 5/6 Channel and panning Right/Left to equal the differences between the two talkers and then controlling the 5/6 Stereo Mix at the VOLUME on the bottom of the panel for that channel.

They currently have two table-booms with two mics and this is where the rub all started - they only have three cables from the stage and they really need four. During any stage changes, they required stagehands to unplug one of the table mics and then plug in the M/C mic - a lot of trouble.

Only one of the table booms OR the M/C mic could be hot at one time.

If you ever needed the M/C, the Podium AND both table booms all at the same time - it wasn't gonna work the way they had it.

Since they had only three XLR-balanced lines running four mics the amp was very unhappy with it at all and would pop the overload.

So - I need to do the R-22 Insulation & Blow-In Crawl through the overhead and drag another coax to the mixer. This is obviously not great (for me) - but necessary choice I guess. Perhaps I can find a young boy to do it.

OK - the two rovers on Channels 1 & 2 are all up-n-running and the MP3 music is all fine and dandy.

That's three channels so far and I am still mixing the podium on the old amp-pots but the stage left M/C mic is running through the mixer on Channel 3, in the center detent of the panning pot.

Channel 1 = wireless rover (ORANGE) MONO, running good
Channel 2 = wireless rover (GREEN) MONO, running good
Channel 3/4 = stage left single M/C mic (WHITE) as MONO, running good
Channel 5/6 = blank I want single Podium mic here (BLUE), MONO
Channel 7/8 = blank I want twin (RED/YELLOW) MONO table booms here
MP3 Stereo IN/OUT is OK (RED/WHITE) - mixed to MONO

IF I convert the Podium XLR to a TRS 1/4" jack and run the Podium mic into the mixer 1/4" MONO, will it still need a pre-amp? I tried a single mic in the 1/4" MONO jack and it worked fine in that jack.

The cable for that test was XLR-1/4" TS.

I tried directly plugging the Podium mic into the 1/4" unbalanced jack on the mixer with another cable and it works great - lots of volume and tone is fine.

I DO find the amp is running very hot though.




.

 

[cavemusic]

...

The two mics on the stage right cannot be controlled by the mic users and there's no place to put someone else to monitor their output.


The whole stage is only 8 feet deep and 22 feet wide and no place to hide anyone in a box or alcove either.

There is no 'back stage'.
There are no 'stage wings'.​

The people who would be at that discussion table are barely capable of using the mics, let alone any panning or mixing controls at the same time - it would be out of their experience and league. These persons change every 20 minutes or so and rotate every week. There's no time for an AV 101 class to teach them.

Actually, after you set up rough levels there, you can control the volume and blend from your board out front.

So - I need to do the R-22 Insulation & Blow-In Crawl through the overhead and drag another coax to the mixer. This is obviously not great (for me) - but necessary choice I guess. Perhaps I can find a young boy to do it.

By coax do you mean another microphone cable? Maybe it's worthwhile running a multi-pair audio cable while you're at it. Somebody in the future may need more channels yet. The biggest hassle is running cable so the extra expense may be worth it in the long run.

IF I convert the Podium XLR to a TRS 1/4" jack and run the Podium mic into the mixer 1/4" MONO, will it still need a pre-amp? I tried a single mic in the 1/4" MONO jack and it worked fine in that jack.

The cable for that test was XLR-1/4" TS.

I tried directly plugging the Podium mic into the 1/4" unbalanced jack on the mixer with another cable and it works great - lots of volume and tone is fine.

Hmm, I guess there is enough gain in the line input, and/or perhaps the mike output is pretty hot. However, there are differences between mike inputs and line inputs aside from the type of connector. Mike inputs generally have about 15 dB higher gain than line inputs, so your level controls will have to be set accordingly. Mike inputs have a different impedance too. It's usually best to have all your mikes connected to mike inputs, and use the line inputs only for ipods, keyboards and the like. But if you can get enough gain maybe this will work well enough. You can get some small mixers with more mike inputs - looks like you really need six mike inputs. I bought a second-hand Berhinger unit with 5 mike inputs for $100. Maybe you can upgrade some time.

 

[SurferJoe46]

TY - I think I'll switch a few cables around and run another cable from the stage to the mixer.

I think I might just put the two table booms on 3/4 with the built-in pre-amp in the mixer and then the two rovers in 1 & 2 and I have a new ART Tube pre-amp I can run the M/C on 5/6 with that.

For the time being though I can run the Dais mic through the amp as usually - it never gets turned down or off the whole show: once it's set and hot - it stays that way until the while system is shut down.

Still rather concerned about the power supply on back of the amp getting hot and thermalling-out - isn't that the result of wrong speaker matching?

I never did anything to the overhead speakers - they are as they were.

 

[cavemusic]

...

Still rather concerned about the power supply on back of the amp getting hot and thermalling-out - isn't that the result of wrong speaker matching?

I never did anything to the overhead speakers - they are as they were.

Connecting speakers with an impedance less than the rating of the amp can cause problems - including damage to the amp. So if the amp is rated for 4 ohms, you can connect 4 ohms, 8 ohms, etc. total load, but not less than 4 ohms. It's a good idea to check that out if you're worried. Most power amps do run pretty warm, and tube amps run quite hot. The power supply probably will run pretty warm all the time no matter what because it is carrying a fair amount of current - that's why most have cooling fins. It's hard to say how hot is too hot though. It is possible there's a problem with the amp internally, but you'd need a good tech to test it out.

 

[TL5]

In my initial response I thought you were adding the mixer in your photo to the existing system and that there was another mixer in the FOH/mix position.

You could still use a small sub mixer for the desktops, sending only the one group feed back to your mixer. It'd be a compromise on the individual mic levels and your FOH mixer would be a 'master' volume control for the group but you could establish that during a test at set-up. There' s never a need to have the talking heads run the mixer.

If you're gonna' add a line, I agree with the previous posts that you should use the coax cable with the short as a pull-wire and pull 3 or 4 new audio lines back to the mixer. It never hurts to have a spare.

Also just a thought; Instead of having those wireless mic receivers plugged in to channels 1 & 2, I'd move those to one of your line inputs, like the proposed 7 & 8 keeping the mic pre available for mic lines. The wireless receivers should have line level outs.

 

[JackANSI]

Those overheads might have transformers meant for a 70v system.. That would probably cause major issues if the amp isn't expecting it...

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