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Title: Why not Aux Controlled Subs?
Post by: Brian Charbobs on January 12, 2014, 06:54:43 pm
I would like to hear from you if what ever reason you are Not using Aux Controlled Subs. What is it you are doing that lets you mix the subs with the tops, and not getting too much being sent to the subs, that should not be there. Thank You!!
Title: Re: Why not Aux Controlled Subs?
Post by: Steve Oldridge on January 12, 2014, 07:27:09 pm
I would like to hear from you if what ever reason you are Not using Aux Controlled Subs. What is it you are doing that lets you mix the subs with the tops, and not getting too much being sent to the subs, that should not be there. Thank You!!
It's called using a DSP.. crossover frequencies/slope set to match your speakers, limiter in place and delay between tops/subs (if warranted).
Title: Re: Why not Aux Controlled Subs?
Post by: Per Sovik on January 12, 2014, 07:37:29 pm
I use it if I can , but sometimes you plug into a house system with no separate sub input, so I tend to high-pass pretty much every microphone as high as possible.
Title: Re: Why not Aux Controlled Subs?
Post by: David Sturzenbecher on January 12, 2014, 08:08:44 pm
I would like to hear from you if what ever reason you are Not using Aux Controlled Subs. What is it you are doing that lets you mix the subs with the tops, and not getting too much being sent to the subs, that should not be there. Thank You!!

Using Aux fed subs is any easy way to mess up a properlly set crossover point. I prefer "bus" fed subs myself.
Title: Re: Why not Aux Controlled Subs?
Post by: Samuel Rees on January 12, 2014, 09:00:15 pm
Using Aux fed subs is any easy way to mess up a properlly set crossover point. I prefer "bus" fed subs myself.

Using aux fed subs can alter the acoustic crossover point for individual channels. A few months ago I started using group/bus fed subs and I haven't looked back.
Title: Re: Why not Aux Controlled Subs?
Post by: Corey Scogin on January 12, 2014, 09:59:12 pm
Using aux fed subs can alter the acoustic crossover point for individual channels. A few months ago I started using group/bus fed subs and I haven't looked back.

I've never used a group fed sub setup.  Do you set the group output level equal to the LR output level?  If not, wouldn't the acoustic crossover point also be affected?

When running subs from a dedicated bus, my channel levels for that bus are always set at unity or -inf and my output level matches the LR bus.  I believe this should avoid the crossover issues, correct?
Title: Re: Why not Aux Controlled Subs?
Post by: Samuel Rees on January 12, 2014, 10:01:33 pm
Yes, from my understanding, that's about the same idea. I prefer to use a group or bus where there is typically a single button assignment to unity, and I can set the group output to unity. I use the mono bus on my Soundcraft Si, a fixed mix on LS9, and groups on Digico and Soundcraft Vi.
Title: Re: Why not Aux Controlled Subs?
Post by: John Chiara on January 12, 2014, 10:43:36 pm
Using aux fed subs can alter the acoustic crossover point for individual channels. A few months ago I started using group/bus fed subs and I haven't looked back.

Same here for the last 7 years.
Title: Re: Why not Aux Controlled Subs?
Post by: Mac Kerr on January 12, 2014, 10:53:55 pm
Using aux fed subs can alter the acoustic crossover point for individual channels.

Why is this bad?

Mac
Title: Re: Why not Aux Controlled Subs?
Post by: Stephen Gregory on January 12, 2014, 11:01:59 pm
Yes, from my understanding, that's about the same idea. I prefer to use a group or bus where there is typically a single button assignment to unity, and I can set the group output to unity. I use the mono bus on my Soundcraft Si, a fixed mix on LS9, and groups on Digico and Soundcraft Vi.

Sorry for being thick, but I don't get it.  Isn't the point of using Aux/group fed subs so that you can tweak the thump when you need it?  It is messing with the crossover point for the channels feeding the group, but isn't that the objective?

If you just leave a sub group set at unity, what benefit does it give over just routing to LR and letting your crossover do its thing?

If you do mess with the sub bus fader, how is that different to tweaking an aux send?

I send a few channels to the mono out on our MixWiz, and I'm pretty happy with the result.  Yes I can make a very bad sound if I boost the sub too much, but used in moderation I like the ability to easily adjust the sub for the different musical styles we get. What am I missing here?
Title: Why not Aux Controlled Subs?
Post by: Samuel Rees on January 12, 2014, 11:02:21 pm
Why is this bad?

Mac

Perhaps I should stay out of the science of it, because I'm really no qualified. I stepped out on the ledge for a moment because I believed that was a one sentence summary of the issue. What I can say is that I heard some people at AES talk about it, so I gave it a go in my workflow, and I feel like I get better behavior around the crossover frequencies of the rigs I'm using than I used to using aux-fed with various send levels. I find this to be especially true on rigs that have been professional processed, but not so much on rigs that are just thrown together. I can share that experience, but I'd like if someone else would explain the science. I believed that was a one sentence summary of the phenomenon I believe I've experienced - please, correct me if I'm wrong. Mac, you were there at the Rational Acoustics discussion I'm referring, perhaps you can share your insight on aux-fed vs group-fed and system tuning.
Title: Re: Why not Aux Controlled Subs?
Post by: Corey Scogin on January 12, 2014, 11:24:23 pm
Sorry for being thick, but I don't get it.  Isn't the point of using Aux/group fed subs so that you can tweak the thump when you need it?  It is messing with the crossover point for the channels feeding the group, but isn't that the objective?

If you just leave a sub group set at unity, what benefit does it give over just routing to LR and letting your crossover do its thing?

My reason for using a dedicated sub bus is not to "tweak the thump" but to keep instruments/vocals out of the subs that don't need to be there.  It helps clean up the bottom end without needing to EQ or high pass those instruments.
Title: Re: Why not Aux Controlled Subs?
Post by: David Sturzenbecher on January 12, 2014, 11:33:22 pm
When running subs from a bus (I like to use the mono bus, especially if there is a handle for it) it gives you one less point to mess up the drive levels (no aux knob, just a bus assignment) .  Yes, you can still push the bus output harder, just like you could have turned the aux master up more.  My reason for this to keep the acoustical crossover point consistant, as my stereo and mono fader would always track. Of course there is value in having your mains and subs phase aligned above and below crossover but sometimes there is only so much time. Plus don't you hate it when you bring your stereo fader down and the subs are still on because the aux doesn't have a easy handle?...DCA/VCAs can help you out here.   I try to avoid using the bus driven method as an easy way to push the low end harder when desired and keep those decisions on the channel strip, where adjustments won't effect crossover points.

I will also admit that I spend more time as a system engineer then mix engineer, so do whatever sounds best to you.
Title: Re: Why not Aux Controlled Subs?
Post by: Ted Christensen on January 12, 2014, 11:38:14 pm
I would like to hear from you if what ever reason you are Not using Aux Controlled Subs. What is it you are doing that lets you mix the subs with the tops, and not getting too much being sent to the subs, that should not be there. Thank You!!

I see people saying it helps them not HPF the channel they need to...BUT IF you have a correctly set up PA with HPF on every channel up to say 400HZ why would you need to use an aux sub?? makes sense to me.

For me just using a HPF at the right place is all i need. I will use aux on occasion but only if i don't have a hpf.
Title: Re: Why not Aux Controlled Subs?
Post by: Tim McCulloch on January 13, 2014, 12:01:13 am
I would like to hear from you if what ever reason you are Not using Aux Controlled Subs. What is it you are doing that lets you mix the subs with the tops, and not getting too much being sent to the subs, that should not be there. Thank You!!

I'm in the business of supplying systems set up the way the client wants.  I'm "sub agnostic".  8)

That said, most often the requests for a full-range setup come from jazz and classical gigs or where there is neither need nor desire for a "haystack" subwoofer response.
Title: Re: Why not Aux Controlled Subs?
Post by: Tim Padrick on January 13, 2014, 01:49:22 am
Cranking the sub may give you a bump because of a "change in the acoustic crossover", but it gives a better result than the boosting of most shelving LF channel EQs, which have a very soft slope - thus boosting at much higher frequencies than you want. 
Title: Re: Why not Aux Controlled Subs?
Post by: Tim Perry on January 13, 2014, 02:44:23 am
I'm in the business of supplying systems set up the way the client wants.  I'm "sub agnostic".  8)

That said, most often the requests for a full-range setup come from jazz and classical gigs or where there is neither need nor desire for a "haystack" subwoofer response.

Many guest "engineers" are befuddled by anything other then full range L/R.

Any DJ/EDM gig I don't even consider it.
Title: Re: Why not Aux Controlled Subs?
Post by: Nicolas Poisson on January 13, 2014, 03:39:08 am
Cranking the sub may give you a bump because of a "change in the acoustic crossover", but it gives a better result than the boosting of most shelving LF channel EQs, which have a very soft slope - thus boosting at much higher frequencies than you want.

Funny, when I compared two ways of setting up my system for heavy low end:
- boost the low output of the processor (after filtering)
- boost the low end at the console (before filtering)
I found that the second solution was better.

Also, when using sub on aux (which I never tried), why is there a change in the acoustic crossover? Isn't the sub aux filtered ? Aren't you supposed to use a three inputs crossover in such cases ?
Title: Re: Why not Aux Controlled Subs?
Post by: Bob Leonard on January 13, 2014, 07:45:08 am
I use a dbx Driverack 4800 for a DSP. The crossover is set correctly, and my subs and upper cabinets respond correctly. If I need more low end I use the board to increase levels or tailor response for the instruments needing help.
Title: Re: Why not Aux Controlled Subs?
Post by: Jeff Bankston on January 13, 2014, 08:02:13 am
first of all i never use subs. i have always run a woofer that could go to at least 50 cps. there are 15" that can go flat to 40. i roll everything off at 40. i have a main pa with 18-12-2 horn. i cross at 130 and 1200 with an ashly xr4001 and i use the low section to roll the bottom end off at 40. the sound is awsome. everthing is nice and clear. long ago midrange soeakers couldnt handle much power and had a short xmax. the turbosound tms3 used a mid 10" that had an xmax of less than 2mm. you couldnt cross them low cause they would over excursion and blow up or freeze, etc. todays good speakers have 10" and 12" mids that handle 400-500 rms watts of power and have an xmax of 8mm-8.5mm and can be run down to 130 real easy or be used a a woofer even though they wont be much good below 100. try setting you lower crossover at 130 and try it. instead of having subwoofers i suggest you buy a 3 way system with 15" woofers that are flat to 40. or use an 18-10(12)-2. besides if you use your aux sends for subs what do you use for monitors ? i use my aux sends for stage monitors.
Title: Re: Why not Aux Controlled Subs?
Post by: TJ (Tom) Cornish on January 13, 2014, 08:47:54 am
Sorry for being thick, but I don't get it.  Isn't the point of using Aux/group fed subs so that you can tweak the thump when you need it?  It is messing with the crossover point for the channels feeding the group, but isn't that the objective?

If you just leave a sub group set at unity, what benefit does it give over just routing to LR and letting your crossover do its thing?

If you do mess with the sub bus fader, how is that different to tweaking an aux send?

I send a few channels to the mono out on our MixWiz, and I'm pretty happy with the result.  Yes I can make a very bad sound if I boost the sub too much, but used in moderation I like the ability to easily adjust the sub for the different musical styles we get. What am I missing here?
It depends on what you're trying to achieve, and what kind of PA you have. 

If you are trying to clean up unwanted LF on channels, bus or aux-fed subs can be advantageous, as you can completely eliminate any sound going to the subs by not assigning them to the sub bus.  Completely eliminating signal to the subs using only the channel HPF may require setting the HPF quite a bit higher than you may want to.

Using aux-fed subs where you have to dial the amount of sub for every channel, basically turns your subs into an effect - they are no longer a cohesive part of your PA.  You may have "adjustability", but I'm not sure that always translates into "control".  IMO, this can make sense if your mains go down to 50Hz or so - then you can truly use your subs as an effect, as your mains can stand alone for all but the lowest stuff.  Most of the time, at least in the lounge, the crossover point is more like 100Hz, and the subs are a pretty critical part of the system.  In that case, I strongly prefer group-fed subs, as it's much easier to keep the sound intact, while you still have the ability to keep things out of the subs that don't need to be there - vocal mics, acoustic guitars, cymbals, etc.
Title: Re: Why not Aux Controlled Subs?
Post by: Brian Charbobs on January 13, 2014, 09:37:32 am
It depends on what you're trying to achieve, and what kind of PA you have. 

If you are trying to clean up unwanted LF on channels, bus or aux-fed subs can be advantageous, as you can completely eliminate any sound going to the subs by not assigning them to the sub bus.  Completely eliminating signal to the subs using only the channel HPF may require setting the HPF quite a bit higher than you may want to.

Using aux-fed subs where you have to dial the amount of sub for every channel, basically turns your subs into an effect - they are no longer a cohesive part of your PA.  You may have "adjustability", but I'm not sure that always translates into "control".  IMO, this can make sense if your mains go down to 50Hz or so - then you can truly use your subs as an effect, as your mains can stand alone for all but the lowest stuff.  Most of the time, at least in the lounge, the crossover point is more like 100Hz, and the subs are a pretty critical part of the system.  In that case, I strongly prefer group-fed subs, as it's much easier to keep the sound intact, while you still have the ability to keep things out of the subs that don't need to be there - vocal mics, acoustic guitars, cymbals, etc.

Well I guess I have some more options to choose from. So your wiring the subs through a Bus to get better overall sound mix with the subs.
Title: Re: Why not Aux Controlled Subs?
Post by: Samuel Rees on January 14, 2014, 02:03:24 pm
Mac, could you drop in with an explanation of the criticism of aux-fed subs we heard from the head of rational acoustics? I was merely fascinated to understand just the fringe of that whole conversation.
Title: Re: Why not Aux Controlled Subs?
Post by: David Sturzenbecher on January 14, 2014, 03:10:39 pm
Mac, could you drop in with an explanation of the criticism of aux-fed subs we heard from the head of rational acoustics? I was merely fascinated to understand just the fringe of that whole conversation.

If you are using smaart (a rational acoustic product) it is difficult to get a reference when using aux fed subs. Thus what the analyzer displays in the low freuqnecy is invalid.
Title: Re: Why not Aux Controlled Subs?
Post by: John Penkala on January 15, 2014, 12:04:49 am
If you are using smaart (a rational acoustic product) it is difficult to get a reference when using aux fed subs. Thus what the analyzer displays in the low freuqnecy is invalid.

I argue that if your sub sends are set up correctly, whether aux fed or otherwise and you actually know how to interpret Smaartlive data you can get very valid measurements. I will go out on a limb and say that 90% of the bad data regarding sub alignment is from acoustical reflections due to poor mic placement or reflections that the operator doesn't or can't "window out".

JP
Title: Re: Why not Aux Controlled Subs?
Post by: Mac Kerr on January 15, 2014, 06:45:22 am
If you are using smaart (a rational acoustic product) it is difficult to get a reference when using aux fed subs. Thus what the analyzer displays in the low freuqnecy is invalid.

It is no more difficult to get a reference with aux fed subs than with subs and mains on one send.

Mac
Title: Why not Aux Controlled Subs?
Post by: David Sturzenbecher on January 15, 2014, 08:44:35 am
What do you use as a reference? One of the left- right?  If you selectively pick and chose what goes to the subs, your measurement will not be accurate as the reference will contain material that you have eliminated from the measurement. I am only talking about in-show FFT measurements. Pre-show tuning is not an issue.


Sent from my iPhone using Tapatalk (http://tapatalk.com/m?id=1)
Title: Re: Why not Aux Controlled Subs?
Post by: Mac Kerr on January 15, 2014, 09:10:53 am
What do you use as a reference? One of the left- right?  If you selectively pick and chose what goes to the subs, your measurement will not be accurate as the reference will contain material that you have eliminated from the measurement. I am only talking about in-show FFT measurements. Pre-show tuning is not an issue.

I don't use in show tuning as I find the signal is rarely usable with more than 1 speaker system at a time on. I would not be using house eq on the subs range at that point in any case.

Mac
Title: Re: Why not Aux Controlled Subs?
Post by: David Sturzenbecher on January 15, 2014, 09:45:27 am
I don't use in show tuning as I find the signal is rarely usable with more than 1 speaker system at a time on. I would not be using house eq on the subs range at that point in any case.

Mac

I find value in monitoring overall response trends from soundcheck, preshow, and show.  I agree with so many sources and variables there is only minimal validity.
Title: Re: Why not Aux Controlled Subs?
Post by: Malcolm Macgregor on January 15, 2014, 08:57:11 pm
One of the reasons against sub on aux might be the fact that the acoustical x-over point changes. Usually the phase response of a sub -> low driver is only matched at 1 point. As the frequency rises or drops the phase won't match.

When both speakers are driven with equal level, the acoustical x-over doesn't change and therefore the summation at x-over stays good (+6 dB when using LR) to keep a flat response.

Example: Raising the sub level without adjusting the phase response to match up might lead to cancellations and thus a reduction in perceived level / sound quality.
Title: Re: Why not Aux Controlled Subs?
Post by: Stephen Gregory on January 15, 2014, 09:54:40 pm
One of the reasons against sub on aux might be the fact that the acoustical x-over point changes. Usually the phase response of a sub -> low driver is only matched at 1 point. As the frequency rises or drops the phase won't match.

When both speakers are driven with equal level, the acoustical x-over doesn't change and therefore the summation at x-over stays good (+6 dB when using LR) to keep a flat response.

Example: Raising the sub level without adjusting the phase response to match up might lead to cancellations and thus a reduction in perceived level / sound quality.

I guess I'm still not understanding.  How does altering the level of the sub affect the amount of cancellation between the sub and tops? I would have thought any phase cancellation frequencies are going to be there no matter what levels you run.  I guess the cancellation might become more obvious if you boost the sub, but surely it was still there before you boosted. Levels don't affect timing/phase/cancellation do they?

I totally take Tom's point about aux-fed subs as an "effect".  That is what I'm doing, and I quite like it.  It's probably not a classy way to handle the low end, but it can work to a first approximation (our tops go down to 52Hz and the subs to 48 - not much in it).
Title: Re: Why not Aux Controlled Subs?
Post by: Sean Chen on January 15, 2014, 10:58:34 pm
I guess I'm still not understanding.  How does altering the level of the sub affect the amount of cancellation between the sub and tops? I would have thought any phase cancellation frequencies are going to be there no matter what levels you run.  I guess the cancellation might become more obvious if you boost the sub, but surely it was still there before you boosted. Levels don't affect timing/phase/cancellation do they?

I totally take Tom's point about aux-fed subs as an "effect".  That is what I'm doing, and I quite like it.  It's probably not a classy way to handle the low end, but it can work to a first approximation (our tops go down to 52Hz and the subs to 48 - not much in it).

I think an improperly setup of aux fed or bus fed sub would introduce phase cancellation above and below the Xover frequency, if the slopes on both sides are not steep enough, and delay is not set right. Having said that, using a very steep LPF on subs would pretty much annihilate this issue.

On the other hand, instead of using bus fed sub or aux fed sub, if an older analog 2nd order crossover is used to separate LR mix to tops and subs, microphone signals will still show up in subs around Xover point. This is much less noticeable if the system crossover is 4th order or steeper.

For me, since my gears do not have steep crossover, (have not quite made the digital leap), I would rather aux/bus feed the subs, and live with a little phase incoherence around 80 Hz for the bass and kick channels, which my ears do not find that disturbing. That sure beats having my subs leaking semi-attenuated 160 Hz fundamental content from vocal mics.
Title: Re: Why not Aux Controlled Subs?
Post by: Jeff Bankston on January 15, 2014, 11:36:13 pm
I think an improperly setup of aux fed or bus fed sub would introduce phase cancellation above and below the Xover frequency, if the slopes on both sides are not steep enough, and delay is not set right. Having said that, using a very steep LPF on subs would pretty much annihilate this issue.

On the other hand, instead of using bus fed sub or aux fed sub, if an older analog 2nd order crossover is used to separate LR mix to tops and subs, microphone signals will still show up in subs around Xover point. This is much less noticeable if the system crossover is 4th order or steeper.

For me, since my gears do not have steep crossover, (have not quite made the digital leap), I would rather aux/bus feed the subs, and live with a little phase incoherence around 80 Hz for the bass and kick channels, which my ears do not find that disturbing. That sure beats having my subs leaking semi-attenuated 160 Hz fundamental content from vocal mics.
i use the Ashly XR###1 crossovers with the 24db/oct LR crossover network. i can turn a woofer amp on and never hear a vocal and i cross at 130. i can turn a mid and high on and sound is crystal clear and verfy detailed and sounds like its the instrument and the singer without a pa. you gotta have a steep slope like the 24db.
Title: Re: Why not Aux Controlled Subs?
Post by: Mac Kerr on January 16, 2014, 04:15:54 am
One of the reasons against sub on aux might be the fact that the acoustical x-over point changes. Usually the phase response of a sub -> low driver is only matched at 1 point. As the frequency rises or drops the phase won't match.

When both speakers are driven with equal level, the acoustical x-over doesn't change and therefore the summation at x-over stays good (+6 dB when using LR) to keep a flat response.

Example: Raising the sub level without adjusting the phase response to match up might lead to cancellations and thus a reduction in perceived level / sound quality.

It does change slightly, but unless the subs and the mains are located close together there is no way to make the phase correct at everywhere because of the geometry, plus, indoors the room response will be so complex with a grid of peaks and nulls due to reflections that it is not the same everywhere anyway.

If you get a better sound with aux fed subs, use them. Even with fairly steep HP filters on the input channels, the sound of vocals in the subs is far more degrading to the sound quality than a small shift in phase response between subs and mains to me.

Mac
Title: Re: Why not Aux Controlled Subs?
Post by: Bob Leonard on January 16, 2014, 07:33:52 am
It does change slightly, but unless the subs and the mains are located close together there is no way to make the phase correct at everywhere because of the geometry, plus, indoors the room response will be so complex with a grid of peaks and nulls due to reflections that it is not the same everywhere anyway.

If you get a better sound with aux fed subs, use them. Even with fairly steep HP filters on the input channels, the sound of vocals in the subs is far more degrading to the sound quality than a small shift in phase response between subs and mains to me.

Mac

I agree 1000%.
Title: Re: Why not Aux Controlled Subs?
Post by: Jonathan Betts on January 16, 2014, 08:21:27 am
I normally run subs left output, tops right output. Hard pan inputs you don't want in the subs, and center pan for bass, kick etc. During sound check,  simply center pan all inputs and see if it makes a difference. Depending on what board you are using there may be a +3db or so increase on the hard panned channels.
Title: Re: Why not Aux Controlled Subs?
Post by: Brad Weber on January 16, 2014, 09:43:32 am
I guess I'm still not understanding.  How does altering the level of the sub affect the amount of cancellation between the sub and tops? I would have thought any phase cancellation frequencies are going to be there no matter what levels you run.  I guess the cancellation might become more obvious if you boost the sub, but surely it was still there before you boosted. Levels don't affect timing/phase/cancellation do they?
They levels, or at least the relative levels, do matter as far as the level or degree of cancellation and/or summation resulting.  For example, you only get full cancellation or summation if the interfering sources have the same relative levels, any difference in relative level will result in something between those extremes and the greater the difference in realtive level, the less the effects of the interference.
Title: Re: Why not Aux Controlled Subs?
Post by: Scott Carneval on January 16, 2014, 09:55:02 am
I guess I'm still not understanding.  How does altering the level of the sub affect the amount of cancellation between the sub and tops? I would have thought any phase cancellation frequencies are going to be there no matter what levels you run.  I guess the cancellation might become more obvious if you boost the sub, but surely it was still there before you boosted. Levels don't affect timing/phase/cancellation do they?

Levels don't directly affect phase, but when you increase the level of the subs WITHOUT increasing the level of the mains you are shifting the acoustical crossover point.  The biggest thing to understand here is the difference between the ELECTRICAL crossover point and the ACOUSTICAL crossover point.  The electrical point is the value that you've entered into your DSP or chosen with the dial on your analog crossover.  But the acoustical point is the point at which the levels of the subs and mains cross, which is where the two speakers will acoustically 'sum' (or cancel). 

In the screenshots below I have chosen a 91hz L-R 24db electrical crossover.  As you can see, when the gain of both outputs is set to 0db the graphs do cross at 91hz.  But as I increase the level of the subs, the frequency at which the subs match the tops also increases.  At +3db it's barely noticeable, maybe 5hz or so.  At +6db, it's gotten worse, it looks like about 10hz (there is a mathematical way to calculate this given the 24db/octave slope of the crossover, but for our purposes we're just going by the graph on the DSP).  Just to illustrate the point, I took the subs to +20db, and now the acoustical crossover has shifted by what looks to be about 30hz.  If the two speakers aren't phase aligned at this frequency, you will experience cancellation somewhere in the room (you will also experience summation somewhere ELSE in the room).  But the reality is, unless all of your drivers are mounted in the same space, you're going to experience SOME cancellation SOMEWHERE in the room. 

As far as how this relates to aux-fed subs, if you set your aux master to the same level as your L/R master, and use post-fader sends, it should never be an issue.  If you desire more db out of your subs you should increase their gain in the DSP, and align your system to account for this.  This probably means lowering the sub electrical crossover point to achieve the desired acoustical crossover point.   
Title: Re: Why not Aux Controlled Subs?
Post by: Samuel Rees on January 16, 2014, 11:53:07 am

Levels don't directly affect phase, but when you increase the level of the subs WITHOUT increasing the level of the mains you are shifting the acoustical crossover point.  The biggest thing to understand here is the difference between the ELECTRICAL crossover point and the ACOUSTICAL crossover point.  The electrical point is the value that you've entered into your DSP or chosen with the dial on your analog crossover.  But the acoustical point is the point at which the levels of the subs and mains cross, which is where the two speakers will acoustically 'sum' (or cancel). 

In the screenshots below I have chosen a 91hz L-R 24db electrical crossover.  As you can see, when the gain of both outputs is set to 0db the graphs do cross at 91hz.  But as I increase the level of the subs, the frequency at which the subs match the tops also increases.  At +3db it's barely noticeable, maybe 5hz or so.  At +6db, it's gotten worse, it looks like about 10hz (there is a mathematical way to calculate this given the 24db/octave slope of the crossover, but for our purposes we're just going by the graph on the DSP).  Just to illustrate the point, I took the subs to +20db, and now the acoustical crossover has shifted by what looks to be about 30hz.  If the two speakers aren't phase aligned at this frequency, you will experience cancellation somewhere in the room (you will also experience summation somewhere ELSE in the room).  But the reality is, unless all of your drivers are mounted in the same space, you're going to experience SOME cancellation SOMEWHERE in the room. 

As far as how this relates to aux-fed subs, if you set your aux master to the same level as your L/R master, and use post-fader sends, it should never be an issue.  If you desire more db out of your subs you should increase their gain in the DSP, and align your system to account for this.  This probably means lowering the sub electrical crossover point to achieve the desired acoustical crossover point.

This is what I thought I was brining up!
Title: Re: Why not Aux Controlled Subs?
Post by: Dave Bednarski on January 16, 2014, 02:55:46 pm
I've tried to follow this... now getting dizzy.

With a pair of KW181s and 153s, am I best to let the cabinets handle the cross over... or do I continue to aux/bus feed the subs from my X32?

I started aux feeding the subs, when I had KSubs and felt I got a tad extra thump out of them in my mix.  Never gone back since upgrading the system... that said, only at higher volumes am I ever really thrilled with the system sound/response.  The low end I am chasing around. 
Title: Re: Why not Aux Controlled Subs?
Post by: g'bye, Dick Rees on January 16, 2014, 03:04:22 pm
Levels don't directly affect phase, but when you increase the level of the subs WITHOUT increasing the level of the mains you are shifting the acoustical crossover point.

THIS is what I was waiting for.  I couldn't remember the threads where this has been brought up, but knew someone would chime in.  And thanks for the visuals.  That's the first time anyone has posted such a graphic representation and it's very helpful to be able to visualize what happens.

Thanks!!!
Title: Re: Why not Aux Controlled Subs?
Post by: Jerome Malsack on January 16, 2014, 03:14:14 pm
With the aux fed subs and your statement that a tad extra thump out of them, are you comparing the Drive rack or speaker processing with a dsp with installed limiter and compressor?   With the dsp processing to protect your speakers and provide eq,  compression, crossover and limiting. it will effect the dynamics.   With Aux fed Sub you will not have the dynamics processing causing some changes to be audible.  So you will have more of the dynamics and attack getting out of the sub.
Title: Re: Why not Aux Controlled Subs?
Post by: Mac Kerr on January 16, 2014, 03:22:41 pm
THIS is what I was waiting for.  I couldn't remember the threads where this has been brought up, but knew someone would chime in.  And thanks for the visuals.  That's the first time anyone has posted such a graphic representation and it's very helpful to be able to visualize what happens.

Thanks!!!

It's good to understand what is happening, but the question I have is, so what? Unless your subs and mains are located close to each other, and you are phase aligning them with an FFT analyzer, and you're in an environment with no reflections, the phase response in the room is going to be more complex than you can account for, and not in phase to begin with.

With the aux fed subs and your statement that a tad extra thump out of them, are you comparing the Drive rack or speaker processing with a dsp with installed limiter and compressor?   With the dsp processing to protect your speakers and provide eq,  compression, crossover and limiting. it will effect the dynamics.   With Aux fed Sub you will not have the dynamics processing causing some changes to be audible.  So you will have more of the dynamics and attack getting out of the sub.

Why wouldn't you have the same dynamics and eq chain as the mains? Just because the subs come off an aux doesn't mean you don't use the same kind of processing on them. They still need the same type of crossover, eq, and dynamics, it is just through a different channel of processing.

Use the method that makes the best sound. For me that is aux fed subs, YMMV.

Mac
Title: Re: Why not Aux Controlled Subs?
Post by: Rob Spence on January 16, 2014, 03:33:17 pm
Why wouldn't you have the same dynamics and eq chain as the mains? Just because the subs come off an aux doesn't mean you don't use the same kind of processing on them. They still need the same type of crossover, eq, and dynamics, it is just through a different channel of processing.

Use the method that makes the best sound. For me that is aux fed subs, YMMV.

Mac

This is why my DSP has 3 (or more) inputs. L, R, Sub.  It doesn't care if the sub input is coming from a bus or an aux (or even low passing it out of a L+R sum).
 
Sent from my iPad using Tapatalk HD
Title: Re: Why not Aux Controlled Subs?
Post by: Scott Carneval on January 16, 2014, 03:53:10 pm
It's good to understand what is happening, but the question I have is, so what? Unless your subs and mains are located close to each other, and you are phase aligning them with an FFT analyzer, and you're in an environment with no reflections, the phase response in the room is going to be more complex than you can account for, and not in phase to begin with.

Use the method that makes the best sound. For me that is aux fed subs, YMMV.

Mac

Right, that's sort of what I was getting at when I said 'unless your mains and subs occupy the same space…'.  I can't agree more with your last sentence.  If used PROPERLY, you'll usually get the best sound by using aux/bus/group (take your pick) fed subs.
Title: Re: Why not Aux Controlled Subs?
Post by: g'bye, Dick Rees on January 16, 2014, 04:25:01 pm
It's good to understand what is happening, but the question I have is, so what? Unless your subs and mains are located close to each other, and you are phase aligning them with an FFT analyzer, and you're in an environment with no reflections, the phase response in the room is going to be more complex than you can account for, and not in phase to begin with.


Mac...

I should have highlighted the part that concerned me.  It was the potential shifting of the acoustic crossover point when boosting subs output.  The phase portion got glossed over as I went for what interested me most.  Seeing the sloped filter creep up as the sub level increased just brought things more into focus for me.  But thanks as always for the clarification.
Title: Re: Why not Aux Controlled Subs?
Post by: Greg_Cameron on January 16, 2014, 04:27:08 pm
Aux fed subs all the way. Occasionally with bass guitars where the low notes have a lot more energy in the subs than wanted, I'll dial down the sub send from detent. Does it shift the relative acoustic crossover point down? Sure. But who cares? If it sounds good, it is good. And for the folks that think 24dB/octave crossovers are relative brick wall for cutting off audio signal, try running a tone sweep through a single band pass with the other drivers turned off some time. Tons of signal above and/or below the knee frequency gets through with standard IR filters. I was shocked years ago when I ran tone sweeps and heard how much audio gets through the LR24 filters in most crossovers above and below the crossover points. A low pass filter at 80Hz on your subs is still allowing quite a bit of energy above that frequency to get into the subs. And a lot of the nasty plosives from vocal mics and various other stage wash lows will get into the subs too. The 12 or 18dB per octave HPFs on your desk on "non-aux sub" systems do allow audible amounts of LF gack into the subs. Heck, even the 24dB per octave HPFs on the Avid venues can, though they're a lot more effective than most.

I'm definitely a fan of not having stuff you don't want in the subs not be able to get there in the first place. It's not hard to do and the benefits are audible.
Title: Re: Why not Aux Controlled Subs?
Post by: Scott Olewiler on January 16, 2014, 05:02:50 pm
THIS is what I was waiting for.  I couldn't remember the threads where this has been brought up, but knew someone would chime in.  And thanks for the visuals.  That's the first time anyone has posted such a graphic representation and it's very helpful to be able to visualize what happens.

Thanks!!!

Of course you'd have the same issue if you reached up and turned up the subs at your DSP or turned the sub amp up during a show. Once the system is balanced you should just leave it alone. If you need more thump there's a channel fader labeled "kick drum" for that. 

Of course it's key to actually balance your system:

Here's a telling story from a show I did last month:  Even though I use the same tops and amp for every show, I'll switch out my subs depending on the room, and then in a small room dial back my tops and use maybe one powered sub, which might vary from room to room.   Of course I "garage" referenced various combinations ahead of time so I pretty much know where to set everything dependent on what I bring in. so I get to this show, set up with only one powered sub and turn the dials where I think they should go; play some reference music at low volume (mistake #1) and tune it by ear (I don't use any audio tools other than an RTA app on my Ipad).

Weather was horrible, band was late and we rushed a sound check, basically just making sure all the mics worked.  Mix was surprisingly good from the start except for this low "wooom" that would occasionally rear it's ugly head. So I'm rolling some low end off one of the guitar cab mics thinking it picking up the sub( and probably was), backing down the drummer's monitor and the problem never manifests long enough to get a good bead on where it's coming from. (before anyone asks, yes I have HPF on all mics) So all night I'm just not happy with the low end, and think the kick drum is causing my problem but don't want to turn it down and lose my "thump".

 About half way thru the last set my helper says he thinks the (powered) sub woofer is turned up too high, walks up on stage, turns it down some, comes back to the board and turns the kick drum up. Mix instantly goes from good to great. And I'm standing there feeling less than smart. We forget how much kick is in the tops. Sometimes you don't need more volume in the subs, you just need more kick drum.

So basically I was plagued all night by what I now believe to be a summing problem somewhere above my crossover point because I had my subs too loud to begin with. I will never forget this.
Title: Re: Why not Aux Controlled Subs?
Post by: g'bye, Dick Rees on January 16, 2014, 05:18:34 pm
Of course you'd have the same issue if you reached up and turned up the subs at your DSP or turned the sub amp up during a show.

It's not an "issue", it's just nice to have a visual representation of what happens when.
Title: Re: Why not Aux Controlled Subs?
Post by: Roland Clarke on January 16, 2014, 05:48:34 pm
Levels don't directly affect phase, but when you increase the level of the subs WITHOUT increasing the level of the mains you are shifting the acoustical crossover point.  The biggest thing to understand here is the difference between the ELECTRICAL crossover point and the ACOUSTICAL crossover point.  The electrical point is the value that you've entered into your DSP or chosen with the dial on your analog crossover.  But the acoustical point is the point at which the levels of the subs and mains cross, which is where the two speakers will acoustically 'sum' (or cancel). 

In the screenshots below I have chosen a 91hz L-R 24db electrical crossover.  As you can see, when the gain of both outputs is set to 0db the graphs do cross at 91hz.  But as I increase the level of the subs, the frequency at which the subs match the tops also increases.  At +3db it's barely noticeable, maybe 5hz or so.  At +6db, it's gotten worse, it looks like about 10hz (there is a mathematical way to calculate this given the 24db/octave slope of the crossover, but for our purposes we're just going by the graph on the DSP).  Just to illustrate the point, I took the subs to +20db, and now the acoustical crossover has shifted by what looks to be about 30hz.  If the two speakers aren't phase aligned at this frequency, you will experience cancellation somewhere in the room (you will also experience summation somewhere ELSE in the room).  But the reality is, unless all of your drivers are mounted in the same space, you're going to experience SOME cancellation SOMEWHERE in the room. 

As far as how this relates to aux-fed subs, if you set your aux master to the same level as your L/R master, and use post-fader sends, it should never be an issue.  If you desire more db out of your subs you should increase their gain in the DSP, and align your system to account for this.  This probably means lowering the sub electrical crossover point to achieve the desired acoustical crossover point.

I would have thought this was true if you "boosted" the level of the sub relative to the mains, however, if they were obstensively at unity, sure this would be no different?
Title: Re: Why not Aux Controlled Subs?
Post by: Mac Kerr on January 16, 2014, 09:07:26 pm
Mac...

I should have highlighted the part that concerned me.  It was the potential shifting of the acoustic crossover point when boosting subs output.  The phase portion got glossed over as I went for what interested me most.  Seeing the sloped filter creep up as the sub level increased just brought things more into focus for me.  But thanks as always for the clarification.

The big concern with the changed crossover point is the shifting of the phase relationship at crossover. Since it is largely unmanageable in most circumstances the whole issue is a tempest in a teapot.

Mac
Title: Re: Why not Aux Controlled Subs?
Post by: David Sturzenbecher on January 16, 2014, 10:10:19 pm
I guess my point from the start is that the crossover point doesn't need to change to begin with. Drive your subs on a bus at the same level you aligned at, our use an aux at zero or off in the same manner. 
Title: Re: Why not Aux Controlled Subs?
Post by: Roland Clarke on January 17, 2014, 05:14:21 am
I guess my point from the start is that the crossover point doesn't need to change to begin with. Drive your subs on a bus at the same level you aligned at, our use an aux at zero or off in the same manner.

This was the point I was making in my previous post, however, I suspect that a good proportion of those that like aux subs like it for the "bump" effect as much as for the lack of driver interaction.  It also brings up two other issues, namely the fact that with vocals and other things that are pretty much HPF at more than an octave above the crossover point the level is going to be so low in the subs, does it matter?  Secondly, the issue of instruments that are potentially borderline, keyboards would be an obvious one, probably many others when you really start to think about it.  I'm not personally advocating one or the other and I have mixed shows with aux subs and many without, I don't remember the ones with aux subs being really any noticeably better or worse, just playing devils advocate.
Title: Re: Why not Aux Controlled Subs?
Post by: Mac Kerr on January 17, 2014, 08:35:47 am
It also brings up two other issues, namely the fact that with vocals and other things that are pretty much HPF at more than an octave above the crossover point the level is going to be so low in the subs, does it matter?  Secondly, the issue of instruments that are potentially borderline, keyboards would be an obvious one, probably many others when you really start to think about it.  I'm not personally advocating one or the other and I have mixed shows with aux subs and many without, I don't remember the ones with aux subs being really any noticeably better or worse, just playing devils advocate.

Try listening to the vocals near the subs. If your subs are flown it probably doesn't make much of a difference vs HPF, but if they are on the ground a makes a big difference.

Mac
Title: Re: Why not Aux Controlled Subs?
Post by: Bob Leonard on January 17, 2014, 08:54:50 am
Call this old school if you want but I spend a lot of time and money tuning my system, 725s and 718s, for the best audio response. I use a dual PA, a dbx 4800, and now a digital board. The entire system is tuned using Smaart when appropriate and the system is not reinvented for every venue I work in.

If I have tuned my system to this point, and with great care and accuracy, why would I insert a variable which can and will effect the overall sound and performance? My point is this. Once my system is tuned I have more than enough control over the sound of each instrument or vocal channel using the board, or board and outboard gear (using my APB). I've tried the aux fed sub thing with mixed results. Where does the huge benefit come from using aux fed subs in my case?
Title: Re: Why not Aux Controlled Subs?
Post by: John Chiara on January 17, 2014, 11:07:20 am
Call this old school if you want but I spend a lot of time and money tuning my system, 725s and 718s, for the best audio response. I use a dual PA, a dbx 4800, and now a digital board. The entire system is tuned using Smaart when appropriate and the system is not reinvented for every venue I work in.

If I have tuned my system to this point, and with great care and accuracy, why would I insert a variable which can and will effect the overall sound and performance? My point is this. Once my system is tuned I have more than enough control over the sound of each instrument or vocal channel using the board, or board and outboard gear (using my APB). I've tried the aux fed sub thing with mixed results. Where does the huge benefit come from using aux fed subs in my case?

Bob, are you using dual subs as well?
Title: Re: Why not Aux Controlled Subs?
Post by: Bob Leonard on January 17, 2014, 11:15:41 am
No, there are no subs used for the vocal half of the dual PA. The 725's provide more than adequate vocal support all by themselves. All subs are assigned to the support of the backline and sound modules.
Title: Re: Why not Aux Controlled Subs?
Post by: Jamin Lynch on January 17, 2014, 11:18:26 am
Try listening to the vocals near the subs. If your subs are flown it probably doesn't make much of a difference vs HPF, but if they are on the ground a makes a big difference.

Mac

Or turn off your tops and leave the subs on. Now speak into a vocal mic and listen to the "rumble" of your voice in the subs. You will get that in the subs even with a step slope.

I often will use aux fed subs when we install a system in a church. Pastors love to walk right in front of the subs when preaching. This will totally eliminate any chance of feedback through the subs. Different story if the subs are flown.
Title: Re: Why not Aux Controlled Subs?
Post by: Samuel Rees on January 17, 2014, 12:18:05 pm
It's because we often run subs hotter than tops for live music, I think. For example, if I choose to HPF a vocal at 100 Hz on a full range system crossed @ 100 Hz with the subs 6db hotter than the tops, some of that <=100 Hz will be going through the subs at +6 compared to the >=100hz going through the tops. In response I take my HPF filter and move it up (or on an LS9 - up a lot), losing some of that 99-125 from the tops I was perhaps looking for. On a group/aux-fed system I can let a channel go as low as the tops will go, without encountering    +xxdB subs because I simply don't assign it. Despite barely hanging on to the science at hand, I'm still comfortable based on this thread and my experience with saying that when I work on professionally tuned systems I get more consistent behavior in the crossover area by using group-fed subs as opposed to aux-fed subs with varying levels.
Title: Re: Why not Aux Controlled Subs?
Post by: Malcolm Macgregor on January 17, 2014, 02:45:11 pm
It does change slightly, but unless the subs and the mains are located close together there is no way to make the phase correct at everywhere because of the geometry, plus, indoors the room response will be so complex with a grid of peaks and nulls due to reflections that it is not the same everywhere anyway.

If you get a better sound with aux fed subs, use them. Even with fairly steep HP filters on the input channels, the sound of vocals in the subs is far more degrading to the sound quality than a small shift in phase response between subs and mains to me.

Mac

I agree, in the real world one would hardly notice a slight cancellation (which only happens on certain spots and actually get's better on other ones)
Title: Re: Why not Aux Controlled Subs?
Post by: Patrick Tracy on January 17, 2014, 06:00:36 pm
I guess I'm still not understanding.  How does altering the level of the sub affect the amount of cancellation between the sub and tops?

The filters themselves introduce group delay that results in phase shift that slopes in opposite directions for high pass and low pass filters. It's common to delay one frequency band so that at the crossover point, which is by definition where the two bands have the same SPL, the phase is compensated for, but as you move up or down from the crossover point the phase error increases. That's not a huge problem because phase cancellation depends on both signals having similar levels, which is only the case at and near the crossover frequency. When you change the level of one band it effectively moves the "equal SPL" point to a frequency at which the two bands are out of phase, which in turn causes deeper cancellation.

That's my best guess anyway...
Title: Re: Why not Aux Controlled Subs?
Post by: Mac Kerr on January 17, 2014, 06:14:50 pm
It's because we often run subs hotter than tops for live music

I don't think it has anything to do with the low frequency haystack effect. Vocals in the subs sound like crap. It doesn't matter if the subs are not run at +6dB relative to the mains. The issue is controlling what goes to the subs, not the level. I use all my groups for other things, and I don't think the variable of each channel to the subs is a problem.

Mac
Title: Re: Why not Aux Controlled Subs?
Post by: Greg_Cameron on January 17, 2014, 07:03:07 pm
I don't think it has anything to do with the low frequency haystack effect. Vocals in the subs sound like crap. It doesn't matter if the subs are not run at +6dB relative to the mains. The issue is controlling what goes to the subs, not the level. I use all my groups for other things, and I don't think the variable of each channel to the subs is a problem.

Agreed. Although 6dB more gak in the subs will be more noticeable ;) I'll tell you one terrible combo I've heard. Studio Live without subs on an aux on my rig. With the 6dB per octave high pass filters on the SL16 and SL24, the vocal boom was intolerable. We have a local promoter/sound guy that prefers to mix his own shows and just rents my racks n' stacks in the venue I have my rig installed in. He loves his Studio Live 16 (he stopped using his SL24 because it's freaked out on him a couple times mid show). He doesn't do aux subs, just runs the mono out of the desk to my sub processing. So much gak I can't stand to be there during his shows.  :o
Title: Re: Why not Aux Controlled Subs?
Post by: Bob Kidd on January 17, 2014, 08:44:13 pm
Never run aux fed subs, would this be difficult to setup? Si 24 into drive rack to amps to speakers is my current configuration. Assuming I would need additional crossover. Thanks
Title: Re: Why not Aux Controlled Subs?
Post by: Greg_Cameron on January 17, 2014, 09:49:01 pm
Never run aux fed subs, would this be difficult to setup? Si 24 into drive rack to amps to speakers is my current configuration. Assuming I would need additional crossover. Thanks

It's not difficult at all. You are correct that you need an extra channel of processing to low pass the subs. Then you drive that extra channel with an aux or spare bus that's assignable on a per channel basis.
Title: Re: Why not Aux Controlled Subs?
Post by: Per Sovik on January 17, 2014, 10:01:47 pm
There are two things that I find to give a better sound quality, aux (or subgroup) subs and cardio subs.

In both cases, there are arguments against it based on how these set-ups "test". We have the acoustic crossover frequency / phase between subs and tops argument with aux subs, and the slightly degraded open field attack "punch" of the cardio set up.

While the arguments might be valid, in a real situation with many open microphones on stage, the reduced stage rumble makes for a much better overall sound and a more defined bass response despite the theoretical downsides.
Title: Re: Why not Aux Controlled Subs?
Post by: Jamie Chappa on January 18, 2014, 02:05:41 am
Never run aux fed subs, would this be difficult to setup? Si 24 into drive rack to amps to speakers is my current configuration. Assuming I would need additional crossover. Thanks
A work around with a drive rack is to pan all nonsub material hard left and sub material center. Out of the drive rack run left high to tops, low right to subs.
Title: Re: Why not Aux Controlled Subs?
Post by: Mark McFarlane on January 18, 2014, 04:59:16 am
Call this old school if you want but I spend a lot of time and money tuning my system, 725s and 718s, for the best audio response. I use a dual PA, a dbx 4800, and now a digital board. The entire system is tuned using Smaart when appropriate and the system is not reinvented for every venue I work in.

If I have tuned my system to this point, and with great care and accuracy, why would I insert a variable which can and will effect the overall sound and performance? My point is this. Once my system is tuned I have more than enough control over the sound of each instrument or vocal channel using the board, or board and outboard gear (using my APB). I've tried the aux fed sub thing with mixed results. Where does the huge benefit come from using aux fed subs in my case?

I suspect if you had something like a Baritone sax downstage in front of the drums and bass amp, you might not want that mic going into the subs...  Yep, contrived example :)
Title: Re: Why not Aux Controlled Subs?
Post by: Mark McFarlane on January 18, 2014, 05:09:56 am
...If you are trying to clean up unwanted LF on channels, bus or aux-fed subs can be advantageous, ...  Most of the time, at least in the lounge, the crossover point is more like 100Hz, and the subs are a pretty critical part of the system.  In that case, I strongly prefer group-fed subs, as it's much easier to keep the sound intact, while you still have the ability to keep things out of the subs that don't need to be there - vocal mics, acoustic guitars, cymbals, etc.

For the record, I've been running aux fed subs for the past decade. 

For those running group-fed subs, I assume you are sending the same group(s) to both tops and subs, and this is the differentiating feature of groups that you prefer over an aux bus that does not go to the mains.

So do you create a special 'subs group' for all instruments you want to send to the subs?   

Or do you have several groups going to a matrix that goes to the subs? 

For example, in my normal setup I have a kick/snare group, a toms group, and a bass group that I could potentially route to a matrix and then to the subs.  Normally I don't put the high toms and snare through the subs but life is full of compromises,...

Or I can keep running aux fed subs, which has worked fine for the last decade for me, except it IS more confusing for the occasional festival events when I am on stage for one band and someone else is operating the console.
Title: Re: Why not Aux Controlled Subs?
Post by: Samuel Rees on January 18, 2014, 10:16:47 am

So do you create a special 'subs group' for all instruments you want to send to the subs?   

This is what I do, and what I've been referring to as group-fed.

Quote
Or do you have several groups going to a matrix that goes to the subs? 

I have not done this.
Title: Re: Why not Aux Controlled Subs?
Post by: Keith Broughton on January 18, 2014, 02:57:36 pm
It's because we often run subs hotter than tops for live music, I think. For example, if I choose to HPF a vocal at 100 Hz on a full range system crossed @ 100 Hz with the subs 6db hotter than the tops, some of that <=100 Hz will be going through the subs at +6 compared to the >=100hz going through the tops. In response I take my HPF filter and move it up (or on an LS9 - up a lot), losing some of that 99-125 from the tops I was perhaps looking for. On a group/aux-fed system I can let a channel go as low as the tops will go, without encountering    +xxdB subs because I simply don't assign it. Despite barely hanging on to the science at hand, I'm still comfortable based on this thread and my experience with saying that when I work on professionally tuned systems I get more consistent behavior in the crossover area by using group-fed subs as opposed to aux-fed subs with varying levels.
I think this is the best argument for aux fed subs.
Title: Re: Why not Aux Controlled Subs?
Post by: Greg_Cameron on January 18, 2014, 03:58:38 pm
Despite barely hanging on to the science at hand, I'm still comfortable based on this thread and my experience with saying that when I work on professionally tuned systems I get more consistent behavior in the crossover area by using group-fed subs as opposed to aux-fed subs with varying levels.

I think I can safely say that most of us folks that use subs on an actual aux send run those channel sends at detent or "unity" for the most part. When doing that, there's no difference in crossover point between using a group bus, aux, or non-aux/bus feed "old school" setup. So the argument is mostly moot. The only time I find myself not doing that on a particular channel is most often when I feel a need to dial down the send level. Usually that's on a bass guitar channel, a floor tom, or a keyboard where the tuning is such that the sub level is overwhelming relative to the tops and a low shelf isn't the call. There's nothing wrong with doing that IMHO. And on rare occasion, I might crank a sub send up for a special effect. Cool to have that control when you want it. Bummer not to if you don't. 8)
Title: Re: Why not Aux Controlled Subs?
Post by: Mark McFarlane on January 19, 2014, 02:37:07 am
I think I can safely say that most of us folks that use subs on an actual aux send run those channel sends at detent or "unity" for the most part. When doing that, there's no difference in crossover point between using a group bus, aux, or non-aux/bus feed "old school" setup...

Greg, I think the concern of the shifting acoustic crossover point is how the sub's aux master send is set relative to the main fader, and how their relative levels may change during the show, not the individual channel sends.

I, like you, often find myself turning down aux sends on bass, sometimes kick or toms depending on how they are tuned and the room,...  I guess I am from the 'use it s an effect' camp for rock shows.
Title: Re: Why not Aux Controlled Subs?
Post by: Greg_Cameron on January 19, 2014, 03:17:52 am
Greg, I think the concern of the shifting acoustic crossover point is how the sub's aux master send is set relative to the main fader, and how their relative levels may change during the show, not the individual channel sends.

If you change a sub send for an individual channel, you are shifting the acoustic x-over point for that channel as gain is gain whether you adjust it from a channel aux or an aux master. Granted you're not changing the alignment of the whole system. But a relative shift is occurring. That said, it really doesn't matter if you're getting the sound you desire..
Title: Re: Why not Aux Controlled Subs?
Post by: Mark McFarlane on January 19, 2014, 03:25:11 am
If you change a sub send for an individual channel, you are shifting the acoustic x-over point for that channel as gain is gain whether you adjust it from a channel aux or an aux master. Granted you're not changing the alignment of the whole system. But a relative shift is occurring. That said, it really doesn't matter if you're getting the sound you desire..

Agreed gain is gain, agreed....
Title: Re: Why not Aux Controlled Subs?
Post by: Mike Karseboom on January 20, 2014, 10:37:58 am
A slightly different slant on this that messed me up a couple of times is that the crossover frequency you choose might need to be lower with group/aux fed subs. 


In the "non-aux" situation where all input channels go the the system processor for separation to subs and tops I was typically setting that crossover frequency to 100Hz.  With 12" powered top (K12) over a single 18" sub (srx718) per side indoors this was giving good results.


When I started putting just kick, floor tom, bass, and (when present) keys into the aux sub feed I created somewhat of a sonic hole from 100Hz down to say 80Hz or so.  Many instruments and even vocals have some content in that frequency range.  So while cleaner sounding way down in the lower octaves the overall system sound lost some "solidness" or "authority" for lack of a better description. 

The 12" mains were being high passed  at 100Hz so they were not producing these frequencies and the subs never got a lot of that content sent to them in the first place.  This was really obvious is someone cut to an acoustic guitar and vocal solo.  It sounded pretty thin.

After moving the crossover point down to 85Hz I think the system sounds fuller and more balanced.  As always YMMV.
Title: Re: Why not Aux Controlled Subs?
Post by: Greg_Cameron on January 20, 2014, 12:39:05 pm
A slightly different slant on this that messed me up a couple of times is that the crossover frequency you choose might need to be lower with group/aux fed subs. 

Agreed. I'm high passing my tops at 60Hz.
Title: Re: Why not Aux Controlled Subs?
Post by: Sndguy (Joel Ashcraft) on January 20, 2014, 02:32:08 pm
Aux fed subs all the way. Occasionally with bass guitars where the low notes have a lot more energy in the subs than wanted, I'll dial down the sub send from detent. Does it shift the relative acoustic crossover point down? Sure. But who cares? If it sounds good, it is good.


+1

This has always been my philosophy.
Title: Re: Why not Aux Controlled Subs?
Post by: Malcolm Macgregor on January 20, 2014, 02:32:39 pm
Agreed. I'm high passing my tops at 60Hz.

Same here, L'Ac 60Hz and D&B 70Hz. Works just as well on other brands to except smaller single top setups, but that's a whole other story :)
Title: Re: Why not Aux Controlled Subs?
Post by: Greg_Cameron on January 20, 2014, 02:35:07 pm
Same here, L'Ac 60Hz and D&B 70Hz. Works just as well on other brands to except smaller single top setups, but that's a whole other story :)

Yeah, if I'm working on rig with weaker LF drivers in the tops, I'll start sweeping the high pass up until the they're not sounding as strained. Then bring the sub low pass up to compensate.
Title: Re: Why not Aux Controlled Subs?
Post by: Luke Geis on January 22, 2014, 02:13:37 am
In my experience...... Assuming we take both approaches, and only simply change the aux fed, or standard full range send, the only difference would be the build up low end and loss of usable power in the subs. If you take two exact systems and run one with a basic full range setup and set it up to perfection and take the same exact system and run it with AUX fed subs ( with exact same DSP settings ETC. ) there will be no perceivable difference........... IF you run all the channels at unity into the aux feeding the sub....... Now lets assume you remove channels all together such as vocals and perhaps things like flute, violin and other such instruments with fundamental frequencies that are only slightly below your crossover point. What happens? You gain the use of that energy back into the sub system ( to a small degree ) and you clean up the low end muck that those instruments were once consuming in the bass bins. And you haven't even touched a knob on the desk yet. The acoustical crossover point is moot at that point if you ask me. The instrument in question will still have it's typical drop off per octave in the other speaker elements and simply don't exist in the the bass bins. BOOOOOO HOOOOOO........

Typically in an AUX fed sub system the standard bass needing instruments such as kick, bass, keys and perhaps the floor tom ( for example ) will be ran at or near unity depending on the user. Not bad right? You still get left and right stereo separation and the subs hit as they normally would with extra headroom available to really pound you if needed ( remember all the other stuff in now not running into the subs ). Now the acoustical crossover will only be marginally off for most of the instruments that you desire in the subs. If the tops are crossed over fairly close the subs there will be less of a difference. If there is a large difference between the subs and tops, then perhaps it may be more noticeable? However I don't think that you will really notice a large acoustical crossover point change unless your running high levels out of the subs. That is to say that your above unity on your aux sends to the subs and there is an obvious increase in sub output for given instruments vs the tops output for the same instruments. The acoustical crossover point will be highly evident if the ratio between sub and top power is vastly different. But you will only notice it in instruments that are fed to booth parts of the system.

So assuming a properly set up system to begin with, there should be no need to worry so much about acoustical crossover points. If your running pre recorded media through the system you will have the aux fed sub tuned for unity and if you mix worth your salt you should be able to acquire similar results. There is no rule that says you cannot send vocals into the subs aux send....... The utilization of high pass filters and judicious use of aux fed subs can yield exceptional results that will probably be better than a typical full range system fed with a full range L/R send. That's what I feel anyway. Having tried booth ways in several configurations, the winner in clarity and power is aux fed subs. The acoustical disconnect between subs and tops is fixed by adding things into the subs if there is need to do so.......
Title: Re: Why not Aux Controlled Subs?
Post by: Jeff Bankston on January 22, 2014, 03:03:18 am
i have a 3 way pa speaker system. 18" woofers , 12" mids , 2" horns. the system is tri-amped. crossover points are 130hz and 1200hz using a 24db/oct electronic. if i run the 18" woofers through an aux feed tell me how thats going to make the system sound better or different than running everthing through the main out ? it doesnt make any sense. last night i connected my 3 way home system to my mackie and did the woofers on the aux. no difference and when i pushed the volume up i had move 2 faders at once instead of one.
Title: Re: Why not Aux Controlled Subs?
Post by: Nicolas Poisson on January 22, 2014, 03:23:34 am
if i run the 18" woofers through an aux feed tell me how thats going to make the system sound better or different than running everthing through the main out ? it doesnt make any sense.

However it made sense for every single member that took part to this topic until now. I advise you to read it, you will get the the answer to your question.

Please, note that when running the woofer on aux, not all instruments are sent to the aux. The sound guy chooses what he sends and what he doesn't. Of course if you send every channel strip at the same level as the master LR bus to the aux, there is no benefit.
If your tests from last night were done using a CD played through the PA, it is reassuring you did not notice any difference.
Title: Re: Why not Aux Controlled Subs?
Post by: Jeff Bankston on January 22, 2014, 04:12:48 am
However it made sense for every single member that took part to this topic until now. I advise you to read it, you will get the the answer to your question.

Please, note that when running the woofer on aux, not all instruments are sent to the aux. The sound guy chooses what he sends and what he doesn't. Of course if you send every channel strip at the same level as the master LR bus to the aux, there is no benefit.
If your tests from last night were done using a CD played through the PA, it is reassuring you did not notice any difference.
yeah i got it , i will try it. i was using a rehersal tape. question > are you not allowing any of the bass guitar or drums in the upeer frequency range ? all my toms and bass drums go up into the mid frequencies. the bass giutar has lots of noted above 200hz. if you cut all that off below say 100hz you've just cut it out of the main pa. that might work good for a small club where the bass and rums dont need be in the foh speakers but several hundred to several thousand is going to present a problem at least for the drums. i'v seen 2000 watt bass rigs. i got blown away at a Manowar concert once. only the drums and vocals were pa'd.
Title: Re: Why not Aux Controlled Subs?
Post by: Mark McFarlane on January 22, 2014, 04:58:36 am
yeah i got it , i will try it. i was using a rehersal tape. question > are you not allowing any of the bass guitar or drums in the upeer frequency range ? all my toms and bass drums go up into the mid frequencies. the bass giutar has lots of noted above 200hz. if you cut all that off below say 100hz you've just cut it out of the main pa. that might work good for a small club where the bass and rums dont need be in the foh speakers but several hundred to several thousand is going to present a problem at least for the drums. i'v seen 2000 watt bass rigs. i got blown away at a Manowar concert once. only the drums and vocals were pa'd.

Instruments that go to the aux fed subs also go to the tops.
Title: Re: Why not Aux Controlled Subs?
Post by: Nicolas Poisson on January 22, 2014, 05:01:42 am
Are you not allowing any of the bass guitar or drums in the uper frequency range ?

Of course you allow that.
- for instrument that go low, you send them in BOTH the aux and the LR mains
- for instruments that need no bass, you send them only in the LR mains

Even "bass" instrument go high (all the more with the harmonics). It is rather common to boost a bass guitar or kick drum around 3kHz to get a punchy sound - take a look at the Beta52 response. 3kHz is way above the typical 100Hz crossover point of the sub, it is even above most mid/hi crossover point.
Title: Re: Why not Aux Controlled Subs?
Post by: Scott Olewiler on January 22, 2014, 06:06:33 am
As if the waters were not muddied already I tried another use for aux fed subs this past weekend. Had a show that consisted of some youth talent, a stand up comic, a few live instruments and some people dancing or singing to pre-recorded tracks.  I set up a compact active sub on stage using another aux send separate from the stage monitors and only put the prerecorded music thru. ( of course pre-recorded music also went thru stage monitors).

This gave the dancers and singers using background tracks a nice beat they could feel on stage while they were performing and allowed me to keep my monitor EQ optimized for voice. Without the aux fed sub monitor I would have had to pump a lot of bass in the monitors just for the recorded tracks.  The FOH subs were on the floor a good 3 ft below stage level so I knew going in the performers on stage were not going to get much coming back from them. 

I'm going to try this technique again with live bands for the drum monitor and see how it works. Might actually sit the drummers monitor on top of the compact sub but I have some concerns about getting some sub sonic spillover into the wedge if it resonates the wedge box.   Mmmm, I wonder if I could talk the drummer into actually sitting on the sub? Can you feel the kick drum now?
Title: Re: Why not Aux Controlled Subs?
Post by: Mark McFarlane on January 22, 2014, 09:00:31 am
....   Mmmm, I wonder if I could talk the drummer into actually sitting on the sub? Can you feel the kick drum now?

http://www.thebuttkicker.com/pro-audio

Title: Re: Why not Aux Controlled Subs?
Post by: jason misterka on January 22, 2014, 10:42:38 am
My experience is similar to Luke's.

Here are my thoughts on it.

I much prefer AUX subs instead of BUS subs due to issues involving stereo sources.  This allows me to sum the stereo sources at -6 and keep the proper proportion.

My favorite though is the variable mono bus on the MIDAS PRO consoles.  Best of both worlds.

When using BUS subs you also have to be careful that you set nominal based on a mono channel source when configuring and aligning the system.

Otherwise I tend to keep my bass and kick at nominal in the subs.  I will sometimes add an appropriate vocal or key or acoustic guitar at a level less than nominal every once in a while.   

For toms, I may add a bit of sub to the high tom, a bit more to the middle tom and set the floor tom at nominal. I know this is not proper but it can be a quick place to end up if the tom sound terrible on their own and you have no time to do a proper soundcheck and apply EQ (or yell at the drummer.)

When the band takes a break and the singer plays an acoustic song, add the guitar to the subs. Maybe the vocal too. But you don't need it there with the rest of the band playing, channels need to mesh with the entire soundscape not just sound good individually.

For the odd day that I am mixing on a club PA or on another company's system and not my own, having a discrete sub send instead of just LR is crucial.  I absolutely understand why artist techs ask for it.  On one three-club mini-tour I was FOH for an artist, all three of the clubs had presets with the subs much more haystacked than even I like.  At one club I had to turn down the subs 12db.  Much easier with a discrete send.

Lastly, my opinion is that unless your subs are crossed over at 100hz or below (and ideally below) I wouldn't bother with aux subs.

Just my take on it.

Jason
Title: Re: Why not Aux Controlled Subs?
Post by: Greg_Cameron on January 22, 2014, 12:02:31 pm
Lastly, my opinion is that unless your subs are crossed over at 100hz or below (and ideally below) I wouldn't bother with aux subs.

Just my take on it.

I tend to agree. If you're crossed too high, you may not have enough bottom for things not being sent to the subs. For Jeff Harrell's setup, aux subs might not be ideal. Now if Jeff decided to take the plunge and use his current "subs" as LF boxes and then added on some subs that reached down into the 20s, it would be a more viable plan. I'd high pass the main rig at 50Hz and then run the aux subs from there on down :)
Title: Re: Why not Aux Controlled Subs?
Post by: Samuel Rees on January 22, 2014, 01:03:05 pm

I much prefer AUX subs instead of BUS subs due to issues involving stereo sources.  This allows me to sum the stereo sources at -6 and keep the proper proportion.

Can you explain this phenomenon in a little more detail?
Title: Re: Why not Aux Controlled Subs?
Post by: Greg_Cameron on January 22, 2014, 01:05:44 pm
Can you explain this phenomenon in a little more detail?

If you have 2 channels of identical signal content sum, you get a +6dB boost in level relative to a single channel. With aux subs, you can dial back 3dB of sub send on each channel to maintain the gain structure without the bump. On a non-variable bus send, you can't do that.
Title: Re: Why not Aux Controlled Subs?
Post by: Tim McCulloch on January 22, 2014, 01:43:14 pm
i have a 3 way pa speaker system. 18" woofers , 12" mids , 2" horns. the system is tri-amped. crossover points are 130hz and 1200hz using a 24db/oct electronic. if i run the 18" woofers through an aux feed tell me how thats going to make the system sound better or different than running everthing through the main out ? it doesnt make any sense. last night i connected my 3 way home system to my mackie and did the woofers on the aux. no difference and when i pushed the volume up i had move 2 faders at once instead of one.

You are using your 18" elements as LF *and* subs.  This works better when the system LF is separate from the subs, Jeff.

The issue is how much "gack" we send to the subs, mostly bleed into microphones that a typical console's 80Hz channel HPF isn't going do much for.  Desks that have sweepable HPF do better, but not every mixer has the same HPF slope (Yamaha had a pretty gentle slope, for example, while Digidesign's is pretty steep).  The other source of sub-gack can come from microphone proximity effect, plosives in the vocals, etc.

I don't think the home theater test was a good one because of the highly manipulated and processed sound track.  You don't have open microphones and a band wailing away behind the vox.

Like I said earlier, this is one tool in the kit.  As the 'system guy' I'm most often asked to configure our systems for left, right, subs, front fills.  Only had a couple of "full range Left & Right" BEs last year.
Title: Re: Why not Aux Controlled Subs?
Post by: Tim McCulloch on January 22, 2014, 01:48:44 pm
My experience is similar to Luke's.

Here are my thoughts on it.

I much prefer AUX subs instead of BUS subs due to issues involving stereo sources.  This allows me to sum the stereo sources at -6 and keep the proper proportion.

My favorite though is the variable mono bus on the MIDAS PRO consoles.  Best of both worlds.

When using BUS subs you also have to be careful that you set nominal based on a mono channel source when configuring and aligning the system.

Otherwise I tend to keep my bass and kick at nominal in the subs.  I will sometimes add an appropriate vocal or key or acoustic guitar at a level less than nominal every once in a while.
   

For toms, I may add a bit of sub to the high tom, a bit more to the middle tom and set the floor tom at nominal. I know this is not proper but it can be a quick place to end up if the tom sound terrible on their own and you have no time to do a proper soundcheck and apply EQ (or yell at the drummer.)

When the band takes a break and the singer plays an acoustic song, add the guitar to the subs. Maybe the vocal too. But you don't need it there with the rest of the band playing, channels need to mesh with the entire soundscape not just sound good individually.

For the odd day that I am mixing on a club PA or on another company's system and not my own, having a discrete sub send instead of just LR is crucial.  I absolutely understand why artist techs ask for it.  On one three-club mini-tour I was FOH for an artist, all three of the clubs had presets with the subs much more haystacked than even I like.  At one club I had to turn down the subs 12db.  Much easier with a discrete send.

Lastly, my opinion is that unless your subs are crossed over at 100hz or below (and ideally below) I wouldn't bother with aux subs.

Just my take on it.

Jason

By using the techniques in BOLD, Jason also relies on the channel strip EQ to shape tone rather than the subwoofer send level.  I bet his board mix recordings sound better as a result.

The other stuff in his post is spot on, too.  If it "wooshed" anyone, re-read his post until your hair stops moving. ;)
Title: Re: Why not Aux Controlled Subs?
Post by: Samuel Rees on January 22, 2014, 02:42:24 pm

If you have 2 channels of identical signal content sum, you get a +6dB boost in level relative to a single channel. With aux subs, you can dial back 3dB of sub send on each channel to maintain the gain structure without the bump. On a non-variable bus send, you can't do that.

Do any consoles compensate for that or panning and etc? Or do we assume this is always true?
Title: Re: Why not Aux Controlled Subs?
Post by: Patrick Tracy on January 22, 2014, 04:04:23 pm
Do any consoles compensate for that or panning and etc? Or do we assume this is always true?

Look up "pan law".

[Edit] I might be making an incorrect assumption about your question. Sorry if that's the case.
Title: Re: Why not Aux Controlled Subs?
Post by: Jeff Bankston on January 22, 2014, 04:22:10 pm
You are using your 18" elements as LF *and* subs.  This works better when the system LF is separate from the subs, Jeff.


I don't think the home theater test was a good one because of the highly manipulated and processed sound track.  You don't have open microphones and a band wailing away behind the vox.

wokrs better when the lf system is seperate from the subs. > thats was what i was thinking. when we start playing again in a few months i will try using the aux for the low end.

home theater not a good test > actually those are for listening to music only and so the gf can play it loud when she pole dances. i still listen to the tv through the tv speakers. the home/rehersal speakers are 15"-10"-2". the play out pa speakers are 18"-12"-2". but i get what your saying. yeah i'll check it out. 
Title: Re: Why not Aux Controlled Subs?
Post by: Scott Olewiler on January 22, 2014, 09:02:48 pm
http://www.thebuttkicker.com/pro-audio

I knew someone would link to that. Being a non-drummer I still can't wrap my head around someone needs to feel something that's connected to their foot or that they can't hear it. I played for 30 years and never once worked with a drummer who needed to hear himself in a monitor until I started doing sound work.
Title: Re: Why not Aux Controlled Subs?
Post by: Greg_Cameron on January 22, 2014, 11:09:48 pm
I knew someone would link to that. Being a non-drummer I still can't wrap my head around someone needs to feel something that's connected to their foot or that they can't hear it. I played for 30 years and never once worked with a drummer who needed to hear himself in a monitor until I started doing sound work.

As a drummer, I never really understood the "need" for a buttkicker. I can see the desire for a large drum fill to get bass guitar solid when you're kit is slightly behind the back line. But growing up touring as a punk rock drummer, I was lucky to have a single crappy wedge in most clubs. So though I provide a big fill for other drummers, I don't really need one myself in most cases. Of course, the lack of having a good monitor and playing with foam earplugs for the past 35 years might explain why i hit super hard and play with 3S sticks (as big as they make them). Maybe if I had a good fill and a Buttkicker all those years, I'd play with smaller sticks and a lot softer instead ;)
Title: Re: Why not Aux Controlled Subs?
Post by: Jeff Bankston on January 23, 2014, 05:15:01 am
i never have my drums in my monitor. if i cant figure out how to hit and what i'm doing after 44 years if playing i should quit ! years ago i learned that none of the guys in Deep Purple used monitors. i dont need a butt kick either. i know what my feet are doing and have recorded almost all gigs and practices over the years. i never kept them after listening to them and used the same cassette tape and kept recording over it until it woe owt(wore out)!
Title: Re: Why not Aux Controlled Subs?
Post by: jason misterka on January 24, 2014, 12:55:30 am
Do any consoles compensate for that or panning and etc? Or do we assume this is always true?

I won't say that no consoles compensate for it, but none of the ones I own do (Avid, Midas PRO, Yamaha M7 and LS9) .  If you set up a stereo subwoofer bus then they do but at that point you are eating up an extra bus, and an extra drive line etc.

Plus you will have the same problem with front fills possibly, depending on your source.  I usually try to derive the front fills from the matrix off of the left and right bus, each set at. -6.  Though as I am not deriving the front fill matrix from a mix of stereo and mono channels, this is less of a big deal.

Jason