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[Jens Droessler]

No, it won't. Why keep people recommending sending the subs separately from the mixer? Just give a stereo signal to the DSP and use a stereo setup. Setup levels correctly (NO boost on the subs, same SPL!), setup phase correctly (if you can't measure it, use one of the tricks to get a good approximation) and do anything like bass boost to taste either in the input section of the DSP,  the output EQ of your mixer or even better, the EQ in the input channel. That's how it's done if you care about the physics involved.

[Mark Wilkinson]

Here goes:

1. Run channel A & B as a basic stereo setup. No there will not be a low pass, but there could be worse things, plus you really could use one anyway.

2. Run channel C & D in mono with the crossover engaged and run the subs out of the appropriate output. This will yield nearly twice the power or about a 3db boost. Not as much boost as many would like, but you can turn the tops down 3db to acquire a 6db difference.

3. Test and see if in bridge mode for C & D that the X-over function still works? If it does this will yield 5X the power to the subs.

4. get a X-over that will allow 3 inputs ( L, R, and mono/subs ) then set it up for your speaker config of L & R with mono subs. Now set the amp up to run A & B in stereo and C & D in bridge mono. Left and Right to A & B and subs to the appropriate +/- output terminals on the C & D outputs. This is the best option and will yield the best results all around.

Thank Luke,

1. yep

2. C & D, in mono, with crossover engaged, only outputs LF to D.  C is HF.  So only one channel is available to drive subs.

3. Tested. Crossover does not work in bridge mode.

4. External x-over seems best to me too.
 I'm thinking to simply send L, R, to the external x-over and let it do the work with three sends to the amp....
....... L high pass and R high pass, to amp A & B in stereo mode. Mono summed Low pass to amp C & D in bridge mono, or just plain mono C&D if bridge is too much power.

[Scott Holtzman]

No, it won't. Why keep people recommending sending the subs separately from the mixer? Just give a stereo signal to the DSP and use a stereo setup. Setup levels correctly (NO boost on the subs, same SPL!), setup phase correctly (if you can't measure it, use one of the tricks to get a good approximation) and do anything like bass boost to taste either in the input section of the DSP,  the output EQ of your mixer or even better, the EQ in the input channel. That's how it's done if you care about the physics involved.

There are many reasons to run aux fed subs and I suggest you take a look at some of extensive discussions about them before you dismiss the tool out of hand.

[Tom Bourke]

No, it won't. Why keep people recommending sending the subs separately from the mixer? Just give a stereo signal to the DSP and use a stereo setup. Setup levels correctly (NO boost on the subs, same SPL!), setup phase correctly (if you can't measure it, use one of the tricks to get a good approximation) and do anything like bass boost to taste either in the input section of the DSP,  the output EQ of your mixer or even better, the EQ in the input channel. That's how it's done if you care about the physics involved.

We recommend it because it works.  Running sound is about compromise.  Sub off aux solves some big problems while only creating some small ones if done right.  It is not that hard to create a good crossover for the signals that are using subs.  Some may choose to use it as an effect.  That's OK too, if it sounds good, it is good.

[Jens Droessler]

Please do not misunderstand what I'm writing here. English is not my native language, so some words might not be the best fit for what I intended to express, and some of the written might be considered as written in anger. It is all written by me while being fully rational. So please read it with a rational head voice. Words in bold are just to emphasize.

We recommend it because it works.  Running sound is about compromise.  Sub off aux solves some big problems while only creating some small ones if done right.  It is not that hard to create a good crossover for tshe signals that are using subs.  Some may choose to use it as an effect.  That's OK too, if it sounds good, it is good.

It only solves problems you cause yourself by what I consider improper use. You compromise where no compromise is needed. And why? Not because it is good, but because you are used to it. I'll try to explain later.

There are many reasons to run aux fed subs and I suggest you take a look at some of extensive discussions about them before you dismiss the tool out of hand.

I read them all at some point. I discussed, thought about them, simulated and tried them many times. There is no good reason for doing it in the modern sound biz, as there is always the better solution. It is as much a tool as a rock is to hammer a nail: You might see it as a tool, but it's not actually the right tool for the job, it's a workaround. Do your homework correctly on the actual physics involved, treat any job no matter the size the same, bring the right tools, and you won't need such crude workarounds. Yes, subs off aux can be done right, but it offers no benefit at all with modern technology. To use another analogy: If you can build a house to stand on its own, why would you build a weak house and use external bracing to make it stand?

A try to explain: The subs off aux method stems from a time when most affordable mixing desks had some aux sends, but compared to nowadays limited EQ possibilities and in most cases not even a locut/highpass per channel. A solution was to highpass the whole main output, put the bass cabs on a post fader aux send and turn them up only for instruments needing them. It was necessary because there were no proper tools to control this situation. It is a workaround.
But now we have all that. We have tuneable locuts and we have four fully parametric EQs per input channel, and that is enough and much better than having ONE fixed frequency highpass (or in some cases none at all, because some peole drive their tops fullrange, only giving the subs a lowpass) for everything. Now you'll say 'No, it's not enough. I still have mud from other channels and even deep vocals coming out of the subs.' And you're right about that. But why is that? It is because you insist of having the boost (to taste) in the bass range only needed for say bassdrum and bass guitar in a rock band on the whole mixed signal (in the DSP controller, the active crossover or simply the level control of the amp or powered sub) instead of those channels' input EQs. Every single bit of signal the subs get will be 6 to 10dB louder than what comes out of the tops from it. It is easy to see why the subs sound mudded up, and also why a 12dB slope locut literally 'won't cut it':  With 6dB boost on the subs, a 12dB locut won't actually work on the frequency you set it to, but a lot higher. It might even leave a bump in the response if tuned lower than the acoustic crossover to the subs or might work down to the crossover freq as expected and then go up in response again if tuned higher than the crossover.
Try it. Spend some work at home into getting your system flat, no boost on the subs. If a -20dBu sine signal at 150Hz will lead to 100dB out of your tops, it should lead at 80Hz to 100dB out of your subs too. Get the phase in the crossover region straight. You only need to do this one time if done correctly, so save or remember those settings. If the room does need corrections because of ring modes and such, do these corrections on the mains EQ, not in the outputs of the DSP or the levels controls on the amps/powered speakers. Leave them alone! And everything having to do with taste (like a 6 to 20dB boost on a bassdrum) should be done in the input channel or a sub group. Now the locuts in the input channels work like they are supposed to do and they should be set as needed.

I know, most won't try it. Many won't even try to understand what I've written, because 'it always worked the way I do it now and I can't think of it getting any better' or whatever. Some of them trying it won't perceive a difference (not having the means to set the PA up correctly for this to work, PA not on a quality level allowing for a clearly notable difference or simply ears that aren't trained enough to hear a difference) and will go back to their old ways. So be it. Anybody can work the way he/she wants. Still the fact remains: This is the physically correct way to do it and you can choose to work with the physics or around them, by trying to bypass them. I take pride in being a sound technician, so I chose the technically correct way.

For those trying and having problems: Write a personal message to me, i'll try to help in detail.

[Scott Holtzman]

Please do not misunderstand what I'm writing here. English is not my native language, so some words might not be the best fit for what I intended to express, and some of the written might be considered as written in anger. It is all written by me while being fully rational. So please read it with a rational head voice. Words in bold are just to emphasize.
It only solves problems you cause yourself by what I consider improper use. You compromise where no compromise is needed. And why? Not because it is good, but because you are used to it. I'll try to explain later.
I read them all at some point. I discussed, thought about them, simulated and tried them many times. There is no good reason for doing it in the modern sound biz, as there is always the better solution. It is as much a tool as a rock is to hammer a nail: You might see it as a tool, but it's not actually the right tool for the job, it's a workaround. Do your homework correctly on the actual physics involved, treat any job no matter the size the same, bring the right tools, and you won't need such crude workarounds. Yes, subs off aux can be done right, but it offers no benefit at all with modern technology. To use another analogy: If you can build a house to stand on its own, why would you build a weak house and use external bracing to make it stand?

A try to explain: The subs off aux method stems from a time when most affordable mixing desks had some aux sends, but compared to nowadays limited EQ possibilities and in most cases not even a locut/highpass per channel. A solution was to highpass the whole main output, put the bass cabs on a post fader aux send and turn them up only for instruments needing them. It was necessary because there were no proper tools to control this situation. It is a workaround.
But now we have all that. We have tuneable locuts and we have four fully parametric EQs per input channel, and that is enough and much better than having ONE fixed frequency highpass (or in some cases none at all, because some peole drive their tops fullrange, only giving the subs a lowpass) for everything. Now you'll say 'No, it's not enough. I still have mud from other channels and even deep vocals coming out of the subs.' And you're right about that. But why is that? It is because you insist of having the boost (to taste) in the bass range only needed for say bassdrum and bass guitar in a rock band on the whole mixed signal (in the DSP controller, the active crossover or simply the level control of the amp or powered sub) instead of those channels' input EQs. Every single bit of signal the subs get will be 6 to 10dB louder than what comes out of the tops from it. It is easy to see why the subs sound mudded up, and also why a 12dB slope locut literally 'won't cut it':  With 6dB boost on the subs, a 12dB locut won't actually work on the frequency you set it to, but a lot higher. It might even leave a bump in the response if tuned lower than the acoustic crossover to the subs or might work down to the crossover freq as expected and then go up in response again if tuned higher than the crossover.
Try it. Spend some work at home into getting your system flat, no boost on the subs. If a -20dBu sine signal at 150Hz will lead to 100dB out of your tops, it should lead at 80Hz to 100dB out of your subs too. Get the phase in the crossover region straight. You only need to do this one time if done correctly, so save or remember those settings. If the room does need corrections because of ring modes and such, do these corrections on the mains EQ, not in the outputs of the DSP or the levels controls on the amps/powered speakers. Leave them alone! And everything having to do with taste (like a 6 to 20dB boost on a bassdrum) should be done in the input channel or a sub group. Now the locuts in the input channels work like they are supposed to do and they should be set as needed.

I know, most won't try it. Many won't even try to understand what I've written, because 'it always worked the way I do it now and I can't think of it getting any better' or whatever. Some of them trying it won't perceive a difference (not having the means to set the PA up correctly for this to work, PA not on a quality level allowing for a clearly notable difference or simply ears that aren't trained enough to hear a difference) and will go back to their old ways. So be it. Anybody can work the way he/she wants. Still the fact remains: This is the physically correct way to do it and you can choose to work with the physics or around them, by trying to bypass them. I take pride in being a sound technician, so I chose the technically correct way.

For those trying and having problems: Write a personal message to me, i'll try to help in detail.

Yes, sometimes non-native English does read as combative and people get aggressive (like me), I need to keep that in mind.  Sorry

We just are going to have to agree to disagree on this one.  If I want to only put a couple of instruments to the subs the tool is an aux fed sub.  I have found it tightens up the low end considerably.  Sure I could go in and tune the low cut on every channel, on every gig but that's going to get old if I am doing 4 bands in one night.

As far as private discussions, heck no.  Put them out in public where the world can benefit.  For every person that contributes I bet 1000 or more read it.  We are contributing to a global brain trust.

By the time I am dead anything relevant I need to share (and many things I am sure most would prefer I kept to my self) will be enshrined on some server somewhere in the digital ether.

[John L Nobile]

I've tried aux fed subs years ago for a few months and it doesn't work for my mix. I've had a few guys use my system last year that wanted that and I told them that I wasn't going to rewire my system for them. They thought I didn't know much about sound cause that's the way to do it these days. They also thought I was crazy to not get a 2 box "line array"  After hearing their mix I thought the same about them lol.
Whatever works for you is great but you should be able to do both. I feel that aux fed subs leads to a bass heavy mix but that is what a lot of modern music is. Seems like kick is the most important thing in some people's mixes. I lean towards vocals as #1 but that's what the show I do is all about.
Last few acts I've seen have been heavy in kick and bass with shrill vocals that didn't sound good and hard to hear. Which
I found weird cause the crowd paid to see the singer not the drummer.
Jens, as Scott said, I'd like to hear more about your reasons and methods. I'm always interested in trying something different. I do a house gig and like to change things up so that I don't get bored or stale.

[Scott Holtzman]

. They also thought I was crazy to not get a 2 box "line array"  After hearing their mix I thought the same about them lol.

Wow, I would hate to think using aux fed subs puts me in the same class as line array box numb nuts that just like pretty shiny things. 

[Luke Geis]

Jens,

    Almost all truly professionally ran PA's are more than likely ran as subs on AUX. There is more than several reasons for this. With today's modern DSP it is much easier to tune a PA than it was 15-20 years ago. Sending the PA a simple 2 channel mix only truly works well with pre recorded media. However with an un-mastered non studio mix being created live, there is a little less sonic control that is available. Proximity effect, mic movement and room characteristics play a huge part in making a live show sound just that. This is why even well done live recordings sound nothing like their studio counterparts. This is only the surface, so lets go deeper.

Just because the mixers these days have 4 band fully parametric EQ with low cuts and every other trick doesn't mean you want/need to use it. Every time a filter is engaged you introduce phase shift ( be it minimal or not ) and are of course at the mercy of the filter design which may introduce other artifacts to the sound when used. The physics of the filter designs mean that phase shift is inevitable if they are used. Doing this to every single channel may start to destroy the entirety of the mix? Perhaps not though, as the phase shift may be negligible? The idea is to get the sound you want from the source, not at the channel strips with aggressive EQ use. Boosts are generally frowned upon and extreme cuts reduce level too much sometimes.

The ultimate goal in system design and optimization is linearity. That is, " what goes in, is what comes out " as a general rule. A well designed and tuned system will not be entirely flat, but will have a very predictable and appealing sonic response in that space. In theory a downward slope from the lows to the highs is favored at around 3db per octave tapering off more after about 10-12khz. No matter how you desire to tune the PA, Linear simply means an even response from one extreme to the other devoid of large humps or cuts in the audio spectrum. It should be smooth and linear, simply put.

This goal can be achieved using either a full range setup or with subs on an aux. No matter what what goes in, the PA reproduces it in the predictable way that it was tuned. So now we are back to the start again where the mixing desk and engineers are what makes or breaks the show. In the case of a simple full range setup the engineer will have to employ more low cuts and perhaps use his EQ filters to tame more of the mics proximity effect. He may even have to employ the Compressor to also tend more to plosives or in the case of heavy shelf or low cut use, he may have an uneven compression sound that does not fit the sonic character of the instrument as much as without the filters in use? If the system is tuned to have less than normal bass ( ideally 3-6db over the mids and highs ) they may have to use filters to add bass, which is somewhat considered taboo. The more you can set a system up to reduce the use of EQ filters the better. Too much of a good thing is still too much.

Now in the case of an Aux fed system, there is no rule that says you can't put everything in the subs still. If both ways of deployment sound the exact same utilizing the same X-over settings and EQ, the only difference being that you can control what goes into each part of the PA, then you have added that much more control to the mix. Now that you can control what goes into the subs entirely, you may not need to employ as many low cut filters or shelves? You may find that you need to use less EQ filters to control content that builds up from Proximity effect on the mics? You may also find that Compression sounds more natural now that you can actually compress the sound more as it is heard? You may also not need to add bass to channels that are lacking because now you can simply dial more up in the subs if needed.

From a Physics standpoint the two ways of deployment only differ in that the Aux fed sub can be used as a separate mix. Between the two deployments, neither is more TECHNICALLY correct than the other. Each one works exactly the same way with physics. Each deployment method has a workaround that must be considered. One requires an extra AUX send and the user to create a mix in that AUX. The other requires you to be more aggressive with EQ filter deployment for sonic control. Tit for Tat if both systems are setup in there respective ways to acquire the exact same sonic response, those two differences will be the only considerations.

Now getting back on track for the OP, the goal was to be able to control the subs output. We offered a way to achieve that with what he already has on hand. His other consideration was having more sub power than tops. We were able to address that as well. From an objective standpoint the suggestion of subs on an aux was the easiest way to get him from point A to B. The only downside being that he won't have a X-over for the tops. That is not the end of the world. In the end the realization is that he will want to have an external X-over to achieve the ultimate results with what he currently has. Whether he runs the system as full range or Subs on AUX is up to him. Being able to do it either way is not a bad goal from a design standpoint. It leaves him with options. The fact of the matter is, subs on Aux takes nothing away from the systems ability. Technically you have twice the amount of control and you don't even have to walk to the amp rack to do it.

The only real complaint I have heard about subs on Aux mixing is that there is a separation from the subs to the tops from the instruments. I think it's just laziness? All you have to do is add what you want into the subs, separation anxiety resolved....... I think it could also be bad system tuning. The PA should sound as one. Remember that content below about 80hz has little to no directionality. That means that you can't really localize where anything below 80hz is coming from. The big point being that if you need something in the subs, with subs on aux, you can put it there; or not.

[John L Nobile]

Wow, I would hate to think using aux fed subs puts me in the same class as line array box numb nuts that just like pretty shiny things.

Didn't mean it that way. Just trying to give you a idea where their headspace was. It's new so it must be better.

[ProSoundWeb Community]