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Author Topic: FOH routing, and 10 other ways to skin a cat  (Read 2963 times)

Paul Rennick

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FOH routing, and 10 other ways to skin a cat
« on: November 22, 2018, 02:08:33 pm »

Hello all, my name is Paul and I'm a first time poster here, but long-time forum user elsewhere.
As you know everyone and their brother seems to have their own best practice so I'm checking my suspicions here.
I can provide more detail if required but I'll try to keep this as "coles notes" as possible to start the discussion.

We run a portable church setup with a small Behringer X32 console, Ultranet (in-ear) monitor stations, 2 self-powered EV Mains, and Matching self-powered EV subs underneath that we run in stereo.  Very typical small-church setup.  The mains and subs are jumpered on the same 2 main feeds from the board (L, and R) with their respective internal Crossovers active.   

I commonly run sound but happened to have a Sunday off the board, but was playing bass-guitar instead. I had a gentleman show up that Sunday that was not a regular to run the board. He proceeded to re-route the FOH so that he was running the same stereo mains to the 2 EV uppers, and a separate 3rd main to one sub at House Left, and then jumpered the L and R subs together.  So he's essentially running stereo mains, and mono subs.  His claim was that he wanted the subs on their own controllable channel.  That way he could route bass guitar and kick through the sub-channel ONLY on a separate feed that was controllable. He claimed that this way he could clean up the vocal presence in the upper mains because the mains didn't have to reproduce everything in the house mix.

He name dropped a big church in the area and said that's how the larger churches do it. 

Now I will admit that I've been doing this for 25-years or so, and have a diploma as a recording engineer, BUT have never ran FOH in a large venue before.  So I'm trying to keep an open mind and think outside my box, but I'm seeing a couple holes in his thought process and it's just not sitting right with me. 

So before I start to tangent on the multitude of reasons that this practice just seems to complicate life for VERY little gain, can someone chime in that has real industry experience on multiple different large venue systems? 
Is this a typical industry best practice?   
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Scott Holtzman

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Re: FOH routing, and 10 other ways to skin a cat
« Reply #1 on: November 22, 2018, 02:12:09 pm »

Hello all, my name is Paul and I'm a first time poster here, but long-time forum user elsewhere.
As you know everyone and their brother seems to have their own best practice so I'm checking my suspicions here.
I can provide more detail if required but I'll try to keep this as "coles notes" as possible to start the discussion.

We run a portable church setup with a small Behringer X32 console, Ultranet (in-ear) monitor stations, 2 self-powered EV Mains, and Matching self-powered EV subs underneath that we run in stereo.  Very typical small-church setup.  The mains and subs are jumpered on the same 2 main feeds from the board (L, and R) with their respective internal Crossovers active.   

I commonly run sound but happened to have a Sunday off the board, but was playing bass-guitar instead. I had a gentleman show up that Sunday that was not a regular to run the board. He proceeded to re-route the FOH so that he was running the same stereo mains to the 2 EV uppers, and a separate 3rd main to one sub at House Left, and then jumpered the L and R subs together.  So he's essentially running stereo mains, and mono subs.  His claim was that he wanted the subs on their own controllable channel.  That way he could route bass guitar and kick through the sub-channel ONLY on a separate feed that was controllable. He claimed that this way he could clean up the vocal presence in the upper mains because the mains didn't have to reproduce everything in the house mix.

He name dropped a big church in the area and said that's how the larger churches do it. 

Now I will admit that I've been doing this for 25-years or so, and have a diploma as a recording engineer, BUT have never ran FOH in a large venue before.  So I'm trying to keep an open mind and think outside my box, but I'm seeing a couple holes in his thought process and it's just not sitting right with me. 

So before I start to tangent on the multitude of reasons that this practice just seems to complicate life for VERY little gain, can someone chime in that has real industry experience on multiple different large venue systems? 
Is this a typical industry best practice?

Look up "aux fed subs" and you will find many discussions.

He is correct, it's common practice, not just in large venues.  The C channel on the x32 is perfect for this application.

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Paul Rennick

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Re: FOH routing, and 10 other ways to skin a cat
« Reply #2 on: November 22, 2018, 02:15:58 pm »

He could have wanted to set his own filters in the board for those respective channels, thus choosing his own crossover frequency between his uppers and lowers but as far as I can tell you can't disable the internal crossover in the self-powered subs anyways.
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Jeremy Young

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Re: FOH routing, and 10 other ways to skin a cat
« Reply #3 on: November 22, 2018, 02:16:44 pm »

Welcome to the PSW forums Paul.  What you're describing is typically called "aux-fed subwoofers".  There are pros and cons to it, but it is a common routing technique (one more tool for the toolbox). 

The internet is full of informative reading if you have the right search terms, so now that you do, I wish you some happy learning!  I did a quick search for the term "aux-fed" on these very forums and came up with 12-pages of threads.
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Luke Geis

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Re: FOH routing, and 10 other ways to skin a cat
« Reply #4 on: November 22, 2018, 02:31:18 pm »

His technique is known as subs on an aux and is probably the most commonly used method done by Pro's the world around. It does have some inherent con's, but the pros outweigh them considerably.

It saves a lot of energy because you delegate the specific tasks to the part of the system that is most efficient at the job. It does and can very much clean up the overall sound of the mix. And lastly, it allows you to tune the subs separately from the mains adding yet another layer of control.

The downsides are as you would expect from a monitoring and playback frame of mind. In live sound, it is generally ideal to reduce the number of sources that any 1 sound comes from and subs on an aux is one way to help in that regard. We are not in the studio and we are not building an audiophile type system. The predominant goal is control and conservation of energy ( headroom ).

To go one step further than subs on an aux with a mono send would be to do subs on an aux fed by a stereo bus and deployed as stereo. Then you can tune what is fed into each sub differently and further improve upon destructive interference.

Conceptually you have to think outside of the box with live sound anyway. The physics, challenges, and issues of using multiple speakers is one that is constantly trying to be worked out. This is why strange end fire sub arrays, cardioid arrays, and other such oddball sub deployments are used. The goal is to fix a problem and improve the outcome. Going with the standard tops over subs approach is essentially the old world way of doing it. Most of the time it works just fine, but there is always a better way.
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Paul Rennick

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Re: FOH routing, and 10 other ways to skin a cat
« Reply #5 on: November 22, 2018, 03:16:29 pm »

Thanks all, so I did the "Aux fed subs" search and read through 6 pages of pro-con argument and understand most everything.  As stated before we are  a church running a portable setup so we have a few volunteers running the system. Most of this would confuse them so i can't say that I would be pushing for this change across the organization but i'm probably going to try this myself.  I find it hard to justify this change across the whole organization while half the volunteers don't know how to use any of the existing dynamics controls.  I've also looked through their parametric EQ settings and most look like a bitcoin run.  24db spikes everywhere. -facepalm

I completely understand now about keeping sub-harmonic vocal stuff out of the subs and not trusting HPF's alone, but I really thought between the HPF on the vocal channel's themselves, plus the internal crossover within the sub, that it would be enough. 
Firstly, my beef was that I thought he was strictly trying to keep low frequencies out of the main, but now I see that that could have been true, but more so it's to keep vocal's out of the subs. 
Secondly when I mix (being a bass player), I really want to hear the crack and attack of the bass strings, and the beater of the kick drum.  Nothing insane or excessive, but it completes the tone of their respective instruments.  I felt by routing these signals to a sub ONLY that was crossed over around 80Hz or whatever the internal is preset at, you would lose this attack. 
     
Maybe I can experiment with using the Mono send for the subs.  That way:
1. I still have main fader control over both.
2. I can assign bass guitar/kick to both.
3. I can assign vocal to the stereo bus only.

That seems like a logical compromise. 
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Jeremy Young

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Re: FOH routing, and 10 other ways to skin a cat
« Reply #6 on: November 22, 2018, 03:51:54 pm »

Hi Paul, sounds like you've got the idea, but to be clear, in an aux-fed sub arrangement you would still be sending the "kick" or "bass" channels to the L/R Mains as well as the Subwoofer aux, so you would not lose the attack that you're worried you'll lose.

Highpass filters (on channels and in system crossovers) are slopes.  There is still energy below the crossover or HPF, and with enough channels contributing this low-end energy even at a low level, it's still energy that the system is trying to recreate.  The larger/louder the system, the more energy there will be down low being reproduced - more than you may realize until you give it a try.  Subwoofers being largely omnidirectional, that extra energy goes back on stage, comes back into those mics, and just further adds to the problem. 

I suggest trying it out yourself and keeping it as a trick up your sleeve, but as you mentioned it may not be the best approach in the hands of the under-trained.  The more experience you gain and comfortable you get, the more tricks you can confidently try to bring your skills to the next level.  Have fun!
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William Schnake

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Re: FOH routing, and 10 other ways to skin a cat
« Reply #7 on: November 22, 2018, 05:46:38 pm »

So before I start to tangent on the multitude of reasons that this practice just seems to complicate life for VERY little gain, can someone chime in that has real industry experience on multiple different large venue systems? 
Is this a typical industry best practice?
Paul, my company does large shows 12,000 plus and small shows 75 - 100 people.  We have been using the 'aux fed sub' method since 2001.  It keeps all of the vocals out of the subs and generally cleans up the mix.  We generally add sub only to kick, bass and keys.

Bill
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Caleb Dueck

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Re: FOH routing, and 10 other ways to skin a cat
« Reply #8 on: November 22, 2018, 06:01:00 pm »



We generally add sub only to kick, bass and keys.

This is very similar to my generic training instructions for aux subs - kick, bass, and pre-recorded music (includes audio from video) is routed to not only the mains but also the subwoofers.  Sometimes keyboard but not often in my limited experience. 

The primary benefit - hard cut most input sources from getting to the subs.   Minor benefit - separate processing and master level of subwoofer send. 

Aux subwoofer send level doesn't replace sub-100Hz EQ. 

Sent from my VS980 4G using Tapatalk

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Geert Friedhof

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Re: FOH routing, and 10 other ways to skin a cat
« Reply #9 on: November 22, 2018, 08:50:10 pm »

Aux fed is one solution, another one is matrix sent subs, and use the HPF on selected channels.
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Nathan Riddle

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Re: FOH routing, and 10 other ways to skin a cat
« Reply #10 on: November 22, 2018, 11:44:46 pm »

Personally, I find myself not in the aux-fed sub camp.

I've read the material, understand how it works, I should probably try it out for kicks.

But I came from a church where they setup the subs on aux and varied the sub level depending on what 'felt' correct. To me, aux fed subs needs to be deployed correctly for it to not be 'weird'. I like my sound to be pure, the system is linear. The system at that church wasn't deployed strategically and gains structure was really off. So I never knew where zero was and we were running with EQ in the channel and sub and mains and it was all convoluted and confusing. Never knew what to do, increase the aux master for more subs, or the channel send, or ch EQ, etc...

Tim MC has pointed out to me that aux fed subs can be used for effect, and if a BE wants it done then who cares how I want it deployed. I agree. Especially with good engineers & festivals & high profile acts.

The church world is slightly different and I find it generally easier to teach a volunteer to turn the channel up and take the HPF to 150+Hz than doing that plus remembering to add the sub send for channels that need it would be confusing for a new guy/gal who shows up to 'push faders'... YMMV

I think, now that I know how to deploy aux subs properly, I could make use of the benefits, but I am always leery of using resources of a system when it isn't necessary.

For your situation, try it. Can't hurt. You'll learn something and that's always good.
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Luke Geis

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Re: FOH routing, and 10 other ways to skin a cat
« Reply #11 on: November 23, 2018, 01:50:27 am »

It is definitely a technique that is not for everyone or even every situation. If it has to be quick and the number of open mics is low, the benefits may not really shine. Subs on aux is tough for some to grasp as well. The thinking that it will sound weird or isn't right from an objective point of view makes the transition harder. The thing is that if you send everything to the subs and set the balance of the subs the way you normally do, it would be exactly as if you went from the mixer into the subs and then into the speaker from the subs pass through.

It is hard for people to grasp that there are no rules when it comes to subs on an aux. You can do whatever you want with them. You want more oomph from the kick but are happy with the click/attack, easy peasy, simply send more kick into the sub aux send. Want less thump and bump, turn it down in the subs. There should be no need to worry about what unity or nominal is. Turn it up or down till it sounds right. You can do this for every single channel, vocals and all. You are in essence treating the subs as a totally separate mix. Think of the mains as that, your main mix. The subs are now used to fill out what the mains don't do. Obviously things like kick, bass and keys will need to have at least some level in the subs.

One thing that I found when doing this is that I needed less overall EQ to get a clean and impactful mix. Now I wasn't neutering the low end on the vocals to keep them from being too boomy. I no longer had to add a 50hz EQ hump to get the thump I wanted, I could simply add more to the subs. The big help with the subs is that now that so little information is going to the subs, I had a little bit more headroom in them.

Here is a video I made outlining why you would want to use subs on aux: https://www.youtube.com/watch?v=ycJfDYpkpMk
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Jean-Pierre Coetzee

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Re: FOH routing, and 10 other ways to skin a cat
« Reply #12 on: November 23, 2018, 06:27:00 am »

Honestly in my opinion if you have a properly installed system with enough headroom it makes no difference. The concept of Aux fed subs just doesn't sit right with me, I won't mind subs on its own channel but it should be linked directly with the main channel volume(as in it should have the same volume).

If you set your crossover correctly then mess with the sub volume then your crossover frequency shifts, it could go up or down depending on many things. You can use a sub going from the mono channel and simply not route stuff to it and that should theoretically be fine.

I want simplicity, if I need to add a bump at 50-80 Hz(I find most lab level subs can't reproduce 50 Hz at any reasonable volume anyway) then there isn't enough rig for the gig to start with. Likewise if the vocals sound boomy in the mains then the crossover frequency is probably way too high anyway. You have a HPF use it, if that doesn't solve your problem then there is a massive problem elsewhere.
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Mike Caldwell

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Re: FOH routing, and 10 other ways to skin a cat
« Reply #13 on: November 23, 2018, 08:41:09 am »

95% of the time if I'm doing bluegrass and the system has subs the subs are aux fed everything else depends on the situation, bands and system configuration.

Joe Pieternella

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Re: FOH routing, and 10 other ways to skin a cat
« Reply #14 on: November 23, 2018, 01:28:31 pm »


If you set your crossover correctly then mess with the sub volume then your crossover frequency shifts, it could go up or down depending on many things.

X32 and probably lots of other boards allow for the "c" bus to have it's level be dependant on the LR faders.

I haven't tried this one but assigning a DCA to LR and whatever out you're using for subs. Or alternatively using a subgroup/DCA as mains assigned to another DCA together with your sub-send.

I tune/balance/run the system with the Subs' master send set to unity and dependent on the LR master. All channel sends to unity.
Now all I need to do is select whether ie not to send a channel to that bus; one press of a button just as easy as phantom power on/off.
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« Last Edit: November 23, 2018, 01:33:47 pm by Joe Pieternella »
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Jeremy Young

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Re: FOH routing, and 10 other ways to skin a cat
« Reply #15 on: November 23, 2018, 05:13:48 pm »

Adjusting the level of the subwoofer send will affect your system crossover, and is not typically recommended.  Sending a "unity" - or whatever you want to call it - level on the kick channel to the mains and sub send (whether aux or matrix) means that the relative balance between subs and tops stays linear.  I'm a firm believer that if you need more 50hz in your kick, you should add that in the channel EQ.  It can be as simple as a post-fader aux-send where that channel aux send is set to zero (unity if you want to call it that) so that as you change the channel level in the mix, the contribution to the subwoofer send moves with it.

There was a time when not every board was digital, channel HPF's were not variable, and depending on the board predetermined HPF slope and frequency you could put a lot of low end energy into the system with a bunch of open vocal mics on, even with the HPF switch engaged.  Might be shocking, but it doesn't even feel that long ago.

For those who have never tried it but are frowning on it, how about this - give it a shot!  It's not for every system or application, but it does give you additional control over the mix compared to a L/R bus only.  When using active subs/tops with built-in crossovers it's quite easy.  If you're using the crossover built into one of those boxes on the feed-thru to the other, it won't work.  Using an external crossover, you'll need to make sure it has enough inputs to handle your routing scheme (so 2inputs minimum if you run mono, 3 minimum if you run stereo tops). 


If your rig uses an unusually high crossover frequency between mains and subs, you may find aux-subs leaving you with a thin sounding mix.  In that case, that's probably not the right system for that technique, or perhaps you need a mid-box in between that is part of your L/R bus and leave the ultra-low-end on the aux sub bus.  Then again, boosting the low-shelf on a channel that's routed only to the mains can still help bring back some of that warmth in my experience.

I personally use aux-fed subwoofers more often than not, because in combat audio you usually have more than enough challenges to deal with on the fly without dealing with excessive low-end buildup.  I like tools that put more control at my fingertips during the event.  I find my channels are either in the subs, or not in the subs, not somewhere in-between.  The first time I tried it with a venue/rig/artist I was really familiar with, I immediately noticed the difference in subwoofer headroom and mix clarity.  That said, I am the sole operator of my systems, so I am the only one who needs to know/understand the routing.
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Luke Geis

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Re: FOH routing, and 10 other ways to skin a cat
« Reply #16 on: November 23, 2018, 06:17:55 pm »

Let's get some of the misconceptions nailed down.

1. The system as a whole is tuned as if it were all ONE system. The subs level, crossover and all are set and that balance should be maintained.

2. Most all digital mixers can link the " C " / " Mono " channel to the L/R. Although you shouldn't really have to mess with that too often anyway.

Some of the tricks I employ to best utilize subs on aux:

1. For the kick, without the kick in the subs, make the kick sound the way you want in the main L/R mix and then add to the subs as needed until the low-end content is to the level you desire.

2. Pretty much the same for everything else. Get it sounding right in the mains, then add the needed amount to the subs.

3. I treat the subs as a totally separate mix. If I only need a little bit of bass guitar or keys, I will only add as much as is needed. Kick is the same. Sometimes you need to send above unity and sometimes you don't.

4. Being certain that the subs send is POST fader is key. Subs on aux do not work well with a Pre fader pick point.
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