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Author Topic: Best Practices for splitting XLR feed in rack (Monitor feed)  (Read 5724 times)

Noah D Mitchell

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Best Practices for splitting XLR feed in rack (Monitor feed)
« on: January 28, 2019, 01:16:31 PM »

Hello,


In one of our venues, looking at installing several floor pockets at various places in the stage for mic feeds and monitor returns.


In the rack where these all terminate, my intention is one panel for inputs, a separate panel for the outputs (returns for monitors to the stage boxes). I would like the ability to patch the monitor feed to any single or a number of boxes (for example, if Mon mix 1 needs to go to floor boxes 3 and 7).


What is the appropriate way to split/mult the XLR signal for quick re-patching to the appropriate boxes?


Ideally a 1-in X 8-out rack mounted solution, with XLR connectors on the front panel (multi-pin creates another step of complexity).


I see Behringer makes a solution that's awfully close to this. Does anyone else?
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Miguel Dahl

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #1 on: January 28, 2019, 01:41:47 PM »

Hello,


In one of our venues, looking at installing several floor pockets at various places in the stage for mic feeds and monitor returns.


In the rack where these all terminate, my intention is one panel for inputs, a separate panel for the outputs (returns for monitors to the stage boxes). I would like the ability to patch the monitor feed to any single or a number of boxes (for example, if Mon mix 1 needs to go to floor boxes 3 and 7).


What is the appropriate way to split/mult the XLR signal for quick re-patching to the appropriate boxes?


Ideally a 1-in X 8-out rack mounted solution, with XLR connectors on the front panel (multi-pin creates another step of complexity).


I see Behringer makes a solution that's awfully close to this. Does anyone else?

I guess the simple solution is to bring the outputs from the desk into a panel, which is parallel wired. Meaning that you can get for instance "mix 1" out of two XLR-M. Normally you can drive two channels in parallel on one amp, if you use passive wedges. So this gives you 4 wedges (2x2, for covering the lip for instace) If any more are needed you can wye. Then have an input patch which feeds the boxes on stage for active wedges or cabled IEM.
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Mike Caldwell

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #2 on: January 28, 2019, 01:57:40 PM »

I think for a simple and solid solution your idea of an output patch panel with the number of connectors that equals the number of floor boxes your going to have would work. The outputs could all be paralleled together.

If the system will be using powered monitors the paralleled outputs are no big deal if someone patched all the monitors to one mix, if the system is using passive monitors then you  would need to keep track of how many monitors are getting  connected to one mix.

Keep the patch bay simple, don't try to use normalling jacks . For line level out XLR females, if your using passive monitors use speakons.

Have the tails from each floor box hanging at the rack and ready to patch.

If you are going to have a digital stage box in the rack and depending on the make and model you could do all of your patching via the mixer's IO patch set up. That would work with either powered or passive monitors, with passive you would need one amp channel per floor box to keep fully patchable though.

Get floor boxes with AC outlets in them.

Taylor Hall

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #3 on: January 28, 2019, 02:15:21 PM »

I guess it really depends on how many individual monitors you have, how many monitor sends you have, and what combination of sends to cabinets you end up with. Kinda echoing what Mike said.

If you're talking about the ultralink, that looks like it would work fine for handling pairs or monitors which is probably the most you'd need per performer, it would also let you break out signal for IEMs and such should that need arise. Also like Miguel said, you can always run your amps in parallel mode (assuming they support this) or just Y-cable off any given monitor send and route those to your amps, the signal degradation is minimal for a single split.

If you ever needed more cloned monitor channels you could use something like a split6 or SP1X3 or maybe look into a matrix switcher, though those get spendy pretty quick as channels count goes up.
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Jonathan Kok

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #4 on: January 28, 2019, 03:27:18 PM »

I'd do what Miguel mentioned, but if you'd rather a pre-manufactured solution, or want transformer isolation on the outputs, there's the RDL RU-MLD4T.
https://www.rdlnet.com/product.php?page=344

XLR I/O on the front
Phoenix I/O on the back
Transformer isolated outputs

Rackmount three of these side-by-side using the RU-RA3R, then patch into them as needed.

There's also the non-transformer version; RU-MLD4.
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Noah D Mitchell

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #5 on: January 29, 2019, 12:15:44 PM »

I'd do what Miguel mentioned, but if you'd rather a pre-manufactured solution, or want transformer isolation on the outputs, there's the RDL RU-MLD4T.
https://www.rdlnet.com/product.php?page=344




Thanks for all the input.


My apologies, I did neglect to mention that the monitors are all active.


The RDL solution looks like a great candidate. Also could cascade multiple units together for an instance where I needed more than 4 feeds of the same mix. My only real concern is the gain knob on the front - that does open up the possibility for fiddling, but it looks like the knob is removable.



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Miguel Dahl

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #6 on: January 29, 2019, 01:00:32 PM »

But why an "amplifier"?

I my head just a splitter would do it. Maybe an active splitter which makes sure you negate the losses in the chain due to more speakers connected. Is it 3dB loss every time you double the splits? I can't remember.. This would make somewhat sure that the Cue-wedge is listening at the same level as the wedges on stage if you have 4 monitors connected.

Maybe something like the Klark 1248?
« Last Edit: January 29, 2019, 01:11:04 PM by Miguel Dahl »
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Chris Hindle

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #7 on: January 29, 2019, 02:42:52 PM »

But why an "amplifier"?

I my head just a splitter would do it. Maybe an active splitter which makes sure you negate the losses in the chain due to more speakers connected. Is it 3dB loss every time you double the splits? I can't remember.. This would make somewhat sure that the Cue-wedge is listening at the same level as the wedges on stage if you have 4 monitors connected.

Maybe something like the Klark 1248?
He's talking Line Lever here.
It's about the impedance loading.
You can generally chain as much as you want as long as the load impedance is better than 10 times the source. Or was it 100....
I know someone will clarify this.
I have successfully bridged 6 or 8 amps together without using line drivers.
(and NO change in level if 1 or 2 get yanked off the chain)
Chris.
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Taylor Hall

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #8 on: January 29, 2019, 03:02:32 PM »

The way I understood it is that it's how the pre in the amp translates the change in the voltage of the audio signal into what gets sent out to the drivers. Since the impedance of most amp pres are in the mid-high hundreds, that makes it easy to split the signal multiple times with minimal to no (discernible) degradation.

Of course this was explained to me years ago in a bar napkin type scenario, so I could be misremembering...
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Peter Kowalczyk

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #9 on: January 29, 2019, 06:02:57 PM »

The way I understood it is that it's how the pre in the amp translates the change in the voltage of the audio signal into what gets sent out to the drivers. Since the impedance of most amp pres are in the mid-high hundreds, that makes it easy to split the signal multiple times with minimal to no (discernible) degradation.

Of course this was explained to me years ago in a bar napkin type scenario, so I could be misremembering...

I'll take a shot at this explanation...

Since the output impedance of the driver and the input impedance of the receiver form a voltage divider, voltage at the receiver is maximized when the output impedance is very small, and the input impedance is very large. 

When we drive multiple high-impedance inputs in parallel, the net input impedance is reduced accordingly, which does, indeed, attenuate the signal level.  However, as long as the output impedance is very low and the input impedance is very high, the result is fairly insignificant.  An example with some randomly chosen devices:

Midas' published output impedance for the DL32 stagebox is 50 ohms.
Meyer Sound's published input impedance for the UM-1P monitor is 10 kOhm.

When a single output drives a single input, we have a voltage divider of 50R <> 10kOhm, which produces [10000/(50+10000)] = 0.995 v/v = 0.04 dB attenuation.
If we were to parallel two monitors, the input impedance is halved, and we have [5000/(50+5000)] = 0.990 v/v = -0.087 dB attn.
If we were to parallel four monitors, the input impedance is quartered, and we have [2500/(50+2500)] = 0.980 v/v = -0.172 dB attn., still less than a quarter dB.
If we were to parallel 10 monitors, the impedance is decimated, and we have [1000/(50+1000)] = 0.95 v/v = -0.44 dB attn., not even a half dB.

This presumes that the impedance of your XLR interconnect is negligibly small, which it ought to be.

So, go ahead an parallel powered speakers with high impedance inputs to your heart's content. 
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Mike Caldwell

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #10 on: January 29, 2019, 06:43:12 PM »


So, go ahead an parallel powered speakers with high impedance inputs to your heart's content.

...........and save yourself money from buying the RDL units with at knob that someone will turn at the wrong time!!

Miguel Dahl

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #11 on: January 30, 2019, 11:23:54 AM »

Righty-O! Thanks!

Electrical is my by far weakest point. This is a quick OT: If I split a microphone into two inputs with a passive splitter, does that 3dB rule come into play? Or am I way outside the ballpark? I really can't remember this, I just remember that there's some sort of 3dB rule when splitting stuff.
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Chris Hindle

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #12 on: January 30, 2019, 12:38:33 PM »

Righty-O! Thanks!

Electrical is my by far weakest point. This is a quick OT: If I split a microphone into two inputs with a passive splitter, does that 3dB rule come into play? Or am I way outside the ballpark? I really can't remember this, I just remember that there's some sort of 3dB rule when splitting stuff.
Personally, I'll split a mic 2-ways. FOH and Monitors.
When a recording split is needed, I go active.
I've had "weirdness" when doing a 4-way passive.
Again, it comes down to mic output impedence driving multiple input impedences paralled. Condensers seem to be more sensitive than dynamics.
Chris.
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Mike Caldwell

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #13 on: January 30, 2019, 12:39:30 PM »

Righty-O! Thanks!

Electrical is my by far weakest point. This is a quick OT: If I split a microphone into two inputs with a passive splitter, does that 3dB rule come into play? Or am I way outside the ballpark? I really can't remember this, I just remember that there's some sort of 3dB rule when splitting stuff.

A two way transformer split will be about 1db of loss on each output, a hardwired split much less.
Input patching with a digital mixers routing, no loss

brian maddox

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #14 on: January 30, 2019, 01:06:57 PM »

....

If we were to parallel 10 monitors, the impedance is decimated...

1000 InterWebs awarded to the Poster for the technically correct use of the word Decimated.
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Russell Ault

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #15 on: January 30, 2019, 02:50:53 PM »

Electrical is my by far weakest point. This is a quick OT: If I split a microphone into two inputs with a passive splitter, does that 3dB rule come into play? Or am I way outside the ballpark? I really can't remember this, I just remember that there's some sort of 3dB rule when splitting stuff.

This is a wattage vs. voltage question. In audio when we're talking about sound levels we're talking about voltage (or other kinds of pressure). Under normal circumstances a microphone's sensitivity (i.e. it's ability to turn a certain amount of air pressure into a certain amount of voltage) is unchanging. If you parallel that microphone's output into two inputs instead of one, the microphone will still produce the same voltage, and both inputs (being in parallel) will see that full voltage, so the signal will appear to be equally strong (i.e. no loss).

The rule about 3dB of attenuation caused by splitting refers to wattage, not voltage, and even then it only happens when the impedance remains constant, which is actually pretty rare. Most of the time in audio when we split a signal we do so in a way that causes the impedance in a circuit to drop, and as a result instead of seeing a wattage decrease from splitting, we actually see a wattage increase. When you plug a second speaker into an amplifier channel, the first speaker doesn't typically get much quieter (unless you're already running the amp ragged); the reason for this is that the amplifier continues to put out the same voltage (remember, it's voltage that represents signal level, even in speakers), but the impedance has been roughly halved, so the amplifier ends up having to put out twice the wattage to maintain the same voltage output. A microphone does roughly the same thing when it's split, doubling its power output as its voltage output remains unchanged.

One thing to note is that the ability to split a signal without loss, while very handy, is electrically inefficient, since it means that under typical circumstances we're not using close to all of a device's possible output power. In audio we've made the decision that this inefficiency is worth it in return for not having to worry about cable impedance matching and not having to worry about the odd split here and there. Even operating inefficiently, most microphones typically produce more than enough signal to ensure decent signal-to-noise ratios, so we just don't worry about it.

So where does the 3dB thing come from? RF. When dealing with wireless microphone signals we are dealing with such minuscule amounts of power that we want to make sure we're using it efficiently. This means that we use impedance-matched devices and cables. It also, importantly, means that we have to use impedance-matched splits. In audio-land, when we split something the voltage is unchanged and the impedance drops so the total wattage rises. With an RF splitter (often technically referred to as a power divider), the output voltage is still unchanging (it's still technically a parallel circuit), but because of impedance matching the impedance isn't allowed to change, either, which means there is a fixed amount of wattage available to the splitter. The splitter divides this wattage evenly between its outputs, which in a two-way split means that each output only gets half the wattage of the input, and half the wattage is 3 dB. Unlike in audio-land, radio receivers define their ability to receive signals based on the wattage of the input signal, not the voltage, which is why a change in wattage suddenly becomes important.

Hope that helps!

-Russ
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David Allred

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #16 on: January 30, 2019, 02:59:57 PM »

1000 InterWebs awarded to the Poster for the technically correct use of the word Decimated.

...so decimated and tithed are the same?
Decimate - 1 per 10 killed.
Tithe - 1 per 10 given, removed, donated, offered, etc.

 
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Dave Garoutte

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #17 on: January 30, 2019, 03:44:31 PM »

Split into ten parts?
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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #18 on: January 30, 2019, 08:06:20 PM »


1000 InterWebs awarded to the Poster for the technically correct use of the word Decimated.


InterWebs... are those like the 'exposures' i get for performing for free?   :P  Can I spend them at your shop??

I meant it to mean 'Divide by 10', equivalent to moving the decimal point to the left one position. 

Apparently the original Latin meaning is far more macabre ('to destroy 1/10th of, e.g. a battalion'), not to mention mathematically different.  Oh sh!t, here we go...)

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Chris Hindle

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #19 on: January 31, 2019, 08:29:07 AM »


Apparently the original Latin meaning is far more macabre ('to destroy 1/10th of, e.g. a battalion'), not to mention mathematically different.  Oh sh!t, here we go...)
Huh. Never looked up the Latin.
Always figured it meant to completely destroy something.
"The crowd was decimated when Axl stormed off the stage mid-set...."
Hahaha
Chris.
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David Allred

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #20 on: January 31, 2019, 11:11:57 AM »

Huh. Never looked up the Latin.
Always figured it meant to completely destroy something.
"The crowd was decimated when Axl stormed off the stage mid-set...."
Hahaha
Chris.

I thought 1 in 10 losses was really a victory.  Apparently not.  I looked up WWII stats.  American losses were only like 2.5%.  I wonder what the D-day stats alone were.
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Miguel Dahl

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #21 on: January 31, 2019, 01:15:40 PM »

I thought 1 in 10 losses was really a victory.  Apparently not.  I looked up WWII stats.  American losses were only like 2.5%.  I wonder what the D-day stats alone were.

From what I found with a quick search KIA were about 2.8%. Allies landed about 156.000 troops, including AB-troops, of which 4414 were KIA (source: DDay.org). The casualties though were naturally much higher. I must admit that I'd think the numbers would be way higher, comparing to how I've pictured the start of the battle through books and movies. MG42's just ripping a hole in the air and flesh throughout the beach into men on the beach with little cover.
« Last Edit: January 31, 2019, 01:21:26 PM by Miguel Dahl »
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brian maddox

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #22 on: January 31, 2019, 11:33:22 PM »

InterWebs... are those like the 'exposures' i get for performing for free?   :P  Can I spend them at your shop??

I meant it to mean 'Divide by 10', equivalent to moving the decimal point to the left one position. 

Apparently the original Latin meaning is far more macabre ('to destroy 1/10th of, e.g. a battalion'), not to mention mathematically different.  Oh sh!t, here we go...)

As the famous ancient quote goes "It's on old code, but it checks out"

I like using Decimated as "divided by ten" even if it's an obsolete usage.  I may even start a campaign to resurrect it.  It'll be like the movement in 1970s USA to Decimalize our measurement systems.
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David Allred

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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #23 on: February 01, 2019, 07:06:36 AM »

As the famous ancient quote goes "It's on old code, but it checks out"

I like using Decimated as "divided by ten" even if it's an obsolete usage.  I may even start a campaign to resurrect it.  It'll be like the movement in 1970s USA to Decimalize our measurement systems.
Ah.   The 70's.  Decilalizing?  I use it all the time.  1.5 inches, 3,5 miles, 10.25 ounces, 5.75 pounds ;D ;D
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Re: Best Practices for splitting XLR feed in rack (Monitor feed)
« Reply #23 on: February 01, 2019, 07:06:36 AM »


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