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Author Topic: Help with Aux-Fed Sub Strategy and Configuration  (Read 19083 times)

Jens Droessler

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Re: Help with Aux-Fed Sub Strategy and Configuration
« Reply #10 on: January 22, 2015, 01:29:50 PM »

Aux-fed subs just complicate things. It adds control where none is needed with sweepable HPFs per channel and potentially even degrades sound (in many ways) --> shifting crossover frequencies, unnecessary overlaps/underlaps and phase issues. Just use the subs crossover and dial in the system to be flat from subs to tops. If the subs aren't sufficient, add more of the same, but turn them all down so the 'flatness' from sub to top is not affected.
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Nils Erickson

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Re: Help with Aux-Fed Sub Strategy and Configuration
« Reply #11 on: January 22, 2015, 01:51:57 PM »

Simple question, lots of correct answers... definitely try both.  I also really prefer aux fed subs as I like the extra control, but it can mean some extra fiddling to get it right as well.
If you are playing mostly restaurants, you may want to be able to get rid of lots of low end easily; it is helpful here to have aux fed subs (I am making an assumption here that diners want to be able to talk and not have the thunder brought down on them).  This way, you don't have to fiddle around on the back of your sub. 
To each their own.  As others said, try it out and be prepared to change it quickly if it isn't working for you.

Cheers,
Nils
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Jens Droessler

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Re: Help with Aux-Fed Sub Strategy and Configuration
« Reply #12 on: January 22, 2015, 02:21:41 PM »

I also really prefer aux fed subs as I like the extra control
I hear this argument a lot. Please explain what's the difference between using a hipass on the top (a fixed one that is) and using a hipass in the channel (an adjustable that is). What would be the difference to the sub between getting no signal from a channel because that channel is not on the subs aux and getting no signal from a channel because the hipass is set accordingly? Ok, you can set the aux of a channel to less of what the mains receive, or higher than the mains, but it makes things worse (as said before, shifts in acoustical crossover frequency, overlaps/underlaps, phase issues. It would only work if you used the aux on unity level on all channels, basically turning subs on and off per channel, but no change in levels) and that's what a sweepable PEQ is for.
The whole concept of aux fed subs comes from a time where even mid sized boards did have no highpass at all, let alone sweepable PEQs. It is obsolete with a full featured digital mixer. And it is just too much of a hassle to get it right. You'd even need an additional EQ for the sub aux, set to exactly the same settings as the mains to have them 'in phase' with each other.
And especially in this case, where the tops have no highpass of their own... Providing the highpass with the GEQ or PEQ of the board? How could this be the fitting counterpart of the subs lowpass? Who will make the phase fit?

So again: A clear no to this! One might like the ease of how to get more or less bass on a channel, but it is not how to do it in a technically correct way.


Quote
If you are playing mostly restaurants, you may want to be able to get rid of lots of low end easily; it is helpful here to have aux fed subs (I am making an assumption here that diners want to be able to talk and not have the thunder brought down on them).  This way, you don't have to fiddle around on the back of your sub. 
Why not use the mains PEQ? Or if you have to use a matrix out?
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Nils Erickson

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Re: Help with Aux-Fed Sub Strategy and Configuration
« Reply #13 on: January 22, 2015, 03:42:57 PM »

I hear this argument a lot. Please explain what's the difference between using a hipass on the top (a fixed one that is) and using a hipass in the channel (an adjustable that is). What would be the difference to the sub between getting no signal from a channel because that channel is not on the subs aux and getting no signal from a channel because the hipass is set accordingly? Ok, you can set the aux of a channel to less of what the mains receive, or higher than the mains, but it makes things worse (as said before, shifts in acoustical crossover frequency, overlaps/underlaps, phase issues. It would only work if you used the aux on unity level on all channels, basically turning subs on and off per channel, but no change in levels) and that's what a sweepable PEQ is for.
The whole concept of aux fed subs comes from a time where even mid sized boards did have no highpass at all, let alone sweepable PEQs. It is obsolete with a full featured digital mixer. And it is just too much of a hassle to get it right. You'd even need an additional EQ for the sub aux, set to exactly the same settings as the mains to have them 'in phase' with each other.
And especially in this case, where the tops have no highpass of their own... Providing the highpass with the GEQ or PEQ of the board? How could this be the fitting counterpart of the subs lowpass? Who will make the phase fit?

So again: A clear no to this! One might like the ease of how to get more or less bass on a channel, but it is not how to do it in a technically correct way.

Why not use the mains PEQ? Or if you have to use a matrix out?

As I said, to each their own... it sounds like a clear "no" to you.
This is the difference for me:  I prefer not to hear any vocal in my sub(or anything I don't want in there, for that matter).  If I high pass my vocals around 125 hz, a common choice for me, I often still hear them a bit in my sub (which crosses over around 80 hz).  Depending on the guitar rig that show up, I may or may not want it at all in the sub as well.  If my HPF were a dramatic cliff, it would work fine. In practice, I find that it doesn't always work for me every time.  I find that this makes my subs sound a little better.

If I want my kick to have more sub, it is easy to do without boosting the low eq or having too much kick attack in the mains.  If I want to very quickly bring down the overall low end, it is simple to fine tune (for me).

Sure, you are right, it changes the acoustic crossover point.  Easy to fix on the L/R out, for me.  Regarding the phase issue, I have more problems with room interaction honestly. But hey, that is my ear.  My drive rack handles the EQ and polarity, making it easy to line things up, even when the tops don't get to sit on the subs, or anywhere near them for that matter.

Technically correct?  I don't care to touch that one.  But hey, it is great that people do things differently.  It is fun to mess around with this stuff and find what works for you. 

In full disclosure, I should also say that I usually set my powered rigs up using the internal crossover, as Debbie said earlier. :)

Anyway, to the OP Alan, there are probably dozens of threads here with dozens of people going back and forth exactly like this; reading them all will only take you so far.  Just try it and decide for yourself.  It is cool that people are passionate about their choices; I use both and wouldn't begrudge anyone for their choice either.

Cheers,
Nils
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Mark Wilkinson

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Re: Help with Aux-Fed Sub Strategy and Configuration
« Reply #14 on: January 22, 2015, 03:55:04 PM »

My understanding was that the crossover is in the sub on these.  The sub has a high pass / full range switch for the pass thru connections.

Normally I run the main output into the sub first, then connect the outputs of the sub to the tops.

Do these tops have a crossover in them?

Manual only shows (as others have mentioned) a switchable HFP in the sub......24 db/oct at 120hz.   48 db at 90hz  for the sub.
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John Penkala

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Re: Help with Aux-Fed Sub Strategy and Configuration
« Reply #15 on: January 22, 2015, 07:35:30 PM »

I'm going to go against the grain here and totally disagree with this statement. Full-range systems with HPF's and Aux Subs are different things and achieve different results. In fact, I use HPF's and Aux Subs together on all 3 of my systems (powered mixer, wedding/corporate system, large 4-way trap rig).

Given the above mentioned gear I would:

1) Dedicate Aux 9 (post fade) to the subs.
2) Send the entire mix to the 712 tops, with a Hi-pass on the Main Mix Graphic EQ set around 90-
    100hz (125 if it's a loud show).
3) Dial in as much low end on Aux 9 as I wanted on low frequency instruments (kick, bass, floor tom, 
    DJ, maybe keys).
4) Set the HP Filters on the channels to whatever I needed them to be. On my iLive, I'll HPF vocals up
    to 160hz, guitar around 125Hz, etc.

For setting instrument levels, I'll first bring them up in the Mains to whatever level I need, then dial in as much sub as I need to add weight to the low frequency instruments. You can also set a LPF on Aux 9 to match the frequency of the HPF on the Mains.

-Mark

       My problem with aux fed subs at the Lounge level is that it most often implemented incorrectly. Many try this as a way to compensate for not having enough "rig for the gig". They try to get that haystacked low end because they don't have enough subs.  To me, it doesn't sound right and often sounds dis-jointed, like the band is playing through two separate sound systems. One for 80hz and below and one for everything else.
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Hanno Meingast

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Re: Help with Aux-Fed Sub Strategy and Configuration
« Reply #16 on: January 22, 2015, 09:07:22 PM »

So, what is the slope on the highpass on the QU?  Is it crossover-like?


Sent from my iPhone using Tapatalk.    Hanno
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Jonathan Betts

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Re: Help with Aux-Fed Sub Strategy and Configuration
« Reply #17 on: January 22, 2015, 09:23:17 PM »

So, what is the slope on the highpass on the QU?  Is it crossover-like?


Sent from my iPhone using Tapatalk.    Hanno

12db octave
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Steve Garris

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Re: Help with Aux-Fed Sub Strategy and Configuration
« Reply #18 on: January 22, 2015, 09:42:49 PM »

I guess I'm in the Aux Fed group. I run a loud Hair Metal band through my PRX rig, and have determined I get more thump and better clarity by keeping almost everything out of the sub's.

I used to use the JBL Xover setting, then run the signal to my 615's (run in full range mode).
I once noticed that vocals were lighting up the sub limiters, even when high-passed at 150 hz, so I decided it was time to get those signals out of the sub's.

I now run my sub's out of the left channel main out, and my tops out of the right channel main out.
I use the Left/Right fader to adjust how much and what goes to the sub's.
I still run the tops in MAIN mode (full range).

It sounds noticeably better to my ears. YMMV.
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Tim McCulloch

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Re: Help with Aux-Fed Sub Strategy and Configuration
« Reply #19 on: January 22, 2015, 10:19:02 PM »

       My problem with aux fed subs at the Lounge level is that it most often implemented incorrectly. Many try this as a way to compensate for not having enough "rig for the gig". They try to get that haystacked low end because they don't have enough subs.  To me, it doesn't sound right and often sounds dis-jointed, like the band is playing through two separate sound systems. One for 80hz and below and one for everything else.

Gosh, pilot error?  Who'd a thunk it?

I think you identified the real problem (or it's the biggest of the problems) - 90% of the time there is simply Not Enough Rig for the Gig®.  How do I know?  Because I did it, 'back in the day' and it doesn't sound any better now that it did then.

It takes a lot of SPL for the PA louder than most guitar players, bassists and drummers play at.  If the stage SPL without PA and vocals is already 110dBC, the PA needs to get the vocals and any other instruments (acoustic guitar, etc) to 116dB, without clipping anything... not the mixer output, not the channel inputs, not any outboard mains EQ or xover, and not the power amps (at least not in all pass bands, and not often).  Every -6dB the band can "give you" in terms of lower stage SPL, the easier and cheaper PA becomes until you reach the point that you need big PA again, to get show SPL for everything.  Pushing too little rig too damn hard is gonna sound bad.

Other replies have mentioned variable high pass filters.  Uh... sometimes they work, sometimes they don't work enough until they work too much.  Yamaha's small and mid-size digimixers (up thru the M7) have 12dB/oct HPF filters and even though you can sweep them they're less than ideal.  Other mixers have steeper filters so YMMV.  I've gotten used to the Digidesign VENUE HPF of 24dB/oct and I miss them when I use other mixers.  And yes, even with subs on an aux....

Sub on Aux are difficult to do on small systems and defeats the "keep it simple, stupid" design intent.  If your mixer will do 18dB/oct HPF or better then don't bother.  If the system is consistently woofy or muddy and no reasonable amount of EQ seems to fix it then maybe subs on aux is one possible solution.

I've only set up a few "full range" systems in the last couple of years and all of them were small-ism bar or meeting room systems.  Everything else, from 400 capacity to 7000 seats had subs on aux either by my preference or was specified by the client or act.
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Re: Help with Aux-Fed Sub Strategy and Configuration
« Reply #19 on: January 22, 2015, 10:19:02 PM »


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