Aux Sub Controlling

[Rob_H]

 

Hi All,

 

Just curious how many of you are doing a seperate mix for your subs using one of your aux outs? Any pitfalls that you have encountered?

 

I am going to be trying this as on the surface, it looks like it makes a lot of sense from a system efficiency perspective, just wanted to know if there is anything to be aware of going into it. I like the idea of only assigning what I actually want going through the subs rather than everything on every channel that is below the crossover point getting there.

 

Thanks,

 

Rob

[dboomer]

Well it costs more and the hookup is a bit more complicated.  But once you've mastered that part there are a bunch of sonic benefits.

 

http://www.peavey.com/support/technotes/concepts/AUX_SUBs.pdf

[Mutha Goose]

 

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Rob_H wrote:

 

 

I like the idea of only assigning what I actually want going through the subs rather than everything on every channel that is below the crossover point getting there.

 

 

The merits/draw-backs of aux-fed subs have been debated here many times (not sure if you can find them or not) and I am sure will be debated again with this post....

But I have to ask about the above statement: why? What do you see as the benefits of this?

[Rob_H]

 

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dboomer wrote:

 

 

Well it costs more and the hookup is a bit more complicated.  But once you've mastered that part there are a bunch of sonic benefits.

 

 

http://www.peavey.com/support/technotes/concepts/AUX_SUBs.pdf

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Thanks Don,

 

I had read that before but thanks for sharing, not concerned about those 2 points as I have the gear needed already, I couldn't see a downside but curious if anyone has discovered something I hadn't thought of.

[Mogwix]

 

1. uses up aux sends (2 for stereo)

2. needs extra return lines on your snake

3. takes longer to set up

If I have a spare post-fade aux and no hi-pass filters on my channel strips... I'll run aux subs. Otherwise, running an aux setup is a complete waste of time because you accomplish exactly the same thing. Aux subs are great when you already have a full-range PA (such as a large array that's flat down to 60Hz without subs) and want to use the subwoofers as a low-frequency effect... but for 95% of what I do, the benefit does not outweigh the (admittedly small) effort required.

[Rob_H]

 

 

The merits/draw-backs of aux-fed subs have been debated here many times (not sure if you can find them or not) and I am sure will be debated again with this post....

 

But I have to ask about the above statement: why? What do you see as the benefits of this?

---

 

 

Thanks,

 

I did a search but I always seem to struggle finding anything relevant with a search here....

 

The biggest benefit I see is not running channels through the subs that don't add anything sonically. I see eliminating unecessary bottom end as improving system efficiency and making a better sounding mix with more punch. I can see the arguement being made that on a digital mixer, I can easily just dial those frequencies out on a per channel basis any way. However, I don't always have the same channel assignments as I work with different people; if I miss assigning it to the aux it will be obviously missing, it won't be so obvious more is there than I want without some further tweaking (if that makes sense to you...it did in my head...lol). I like to focus my effort on improving the sound of every show to the best I can, I guess I see this approach as one way to start a little further ahead on that curve, especially for one-nighter shows with groups I don't know that well.

[RoadRanger]

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Mogwix wrote:

1. uses up aux sends (2 for stereo)

2. needs extra return lines on your snake

3. takes longer to set up

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#1 - who runs stereo subs? And shoot me if I need more than 5 floor monitor mixes (subject to change if IEM's involved).

#2 I run my crossover at FOH so same # sends - but don't use a snake these days anyways.

#3 I usually cheat and use the GEQ's in the board  instead of bringing a crossover so it's actually less time to set up, not more. YMMV .

[StratGuy22]

Nope. I let my crossover do its job instead.

 

[dboomer]

 

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Mogwix wrote:

 

 

 

 

If I have a spare post-fade aux and no hi-pass filters on my channel strips... I'll run aux subs. Otherwise, running an aux setup is a complete waste of time because you accomplish exactly the same thing.

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 I would mostly disagree with that.  It may seem similar depending on how you run your system, but using a seperate crossover for the subs and no way to get unwanted sound into them would be a high pass with a brickwall cutoff as opposed to the more common 6-18 dB/oct slopes.

 

So in the case of having only a 6 dB/oct HP filter on your channel strip and only a 6 dB boost to the level of your subs you have effectively have zero HP as opposed to infinite with aux subs.  In the same case if you have 12 dB/octave HP filters (Mixwiz) you are only rolling off about 4 db at 50 Hz as opposed to infinite exclusion into the sub itself.

 

So it is definitely not the same.

 

[Don Davis]

Since we use 6 of our 8 auxs for wedges and 2 for FX we use a group out for the sub feed. On the 01v96 I set the ratio of sub to tops using either program music or pink then link the main fader and group fader so they follow each other. Then assign what ever channel you wish to the group. Kind of a set and forget.

This has helped us tame a lot of LF build up on stage and standing wave poblems with one venue we do often. All this can be accompplished with crossover and EQ but I'm very happy with bus fed subs and only go back when I have no choice.

[Pro Sound Guy]

This reminds of the first time I saw an Aux fed sub setup in a church.

My inner thoughts lest I corrupted myself was...WTF is this and why TF?

I guess I feel the same way today as I did then

 

 

[agedhorse]

First of all, using a group does not give you proportional control of sub level on an input by input basis... The most valuable aspect of aux fed subs.

 

Second, you need to use identical crossovers when doing this. Filter implementation between different brands and even models is way too unpredictable to give reliable acoustic results.

 

It doesn't have to be that much more hassle, but setting up for a one-off date adds the need to set an additional sub aux mix.

 

If you don't have spare post fader auxs, that's a major obsticle.

[Dookietwo]

I've been running Aux fed subs for 15 years or so now. I like it. Its pretty easy to try if you have a spare crossover and an Post Fade Aux or Mono out. As another has mentioned you can always use the Left master to feed the tops and Right master to feed the subs. Pan to center the channels you want to go to the subs.

Try it. If you like it use it. If not then its just as easy to go back to a basic setup.

Dookietwo

[ewizard]

Here is some insight on AUX fed subs. This will get technical. First and foremost it adds only a small amount of cost to the system because of a need for additional processing. If you run a powered system that has crossovers built in already, your golden! It does eat up an AUX that could be used for monitors, or perhaps an FX send? However if you can't afford a decent dual engine FX unit, then AUX fed subs are the least of your concerns. If you need monitors to the degree that an AUX fed sub is an issue, you already Need a bigger mixing desk.

 

AUX fed subs should be done post fader/post EQ. This is so that changes made at the channel strip effect the sub mix proportionally. There should be separate processing as well for the sub send. Things like EQ, crossover points and limiting will be done differently than the mains and you need to be able to control them separately. Once AUX fed subs are setup, you should find that you have added clarity and punch, as well as increased headroom in the sub amps!

 

Many people think of high pass and low pass filters as being a cure all fix to an underlying issue. They are not. Most filters have what is known as a slope. You may have heard things like -12db per octave, or 4th order filter? The thing that needs to be understood is that when the HP filter is engaged, the 80Hz / 100Hz nomenclature only means that is the corner frequency at which  attenuation begins to occur. After that its attenuated at a pre determined ratio per octave. A -12db per octave filter means that attenuation of 12db will occur at every octave before, or after the corner frequency. In the case of a HP filter with a corner frequency of 80Hz, the incoming signal will have its energy reduced by 12db at 40hz and by 24db at 20hz. This is not exactly a lot of attenuation when you look at it from a per octave basis. In the case of a conventional system setup, there can still be a lot of unneeded low energy content being fed to the subs. This is of course amplified needlessly and eats up potential headroom.

 

By feeding the subs via an Auxiliary, you can pick which instruments low energy content will be amplified. This means less overall low end content and added clarity. This also means increased headroom which allows for more volume of the instruments that you select to be amplified. You increase system efficiency in the low end and reduce the low end reproduction in the room which also helps ad clarity and definition to the entirety of the mix.

 

The preferred method in which to mix Aux fed subs into the system is rather simple. First listen to the instrument in the Mains with the sub send off and then after getting the desired sound, simply add the sub send from that channel strip to the desired level. A well tuned system should require little to no work on the channel strip after it sounds good in the mains. I find that less is more and if you can get your system tuned relatively flat, you should have no issues implementing Aux fed subs. 

[Rob_H]

 

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agedhorse wrote:

 

First of all, using a group does not give you proportional control of sub level on an input by input basis... The most valuable aspect of aux fed subs.

 

 

 

Second, you need to use identical crossovers when doing this. Filter implementation between different brands and even models is way too unpredictable to give reliable acoustic results.

 

 

 

It doesn't have to be that much more hassle, but setting up for a one-off date adds the need to set an additional sub aux mix.

 

 

 

If you don't have spare post fader auxs, that's a major obsticle.

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I need to get better at sharing the whole story...lol...I have a second dbx PA+ on order so will have matching units and relegate the 1001 back to back-up duty

Please explain more of what you mean on the first point; I thought the sub group would be relative to channel positions? When I use subgroups today for drums (with drums assigned only to subgroup, not subgroup and mains) I don't find the level relationship to each other changing as I raise the group relative to the rest of the mix; why would it be different using them for sub control? Again, not questioning your position, just trying to wrap my head around it.