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Author Topic: Why not Aux Controlled Subs?  (Read 31255 times)

Patrick Tracy

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Re: Why not Aux Controlled Subs?
« Reply #60 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...

Mac Kerr

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Re: Why not Aux Controlled Subs?
« Reply #61 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
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Greg_Cameron

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Re: Why not Aux Controlled Subs?
« Reply #62 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
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Bob Kidd

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Re: Why not Aux Controlled Subs?
« Reply #63 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
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Greg_Cameron

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Re: Why not Aux Controlled Subs?
« Reply #64 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.
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Per Sovik

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Re: Why not Aux Controlled Subs?
« Reply #65 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.
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Jamie Chappa

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Re: Why not Aux Controlled Subs?
« Reply #66 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.
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Mark McFarlane

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Re: Why not Aux Controlled Subs?
« Reply #67 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 :)
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Mark McFarlane
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Mark McFarlane

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Re: Why not Aux Controlled Subs?
« Reply #68 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.
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Mark McFarlane
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Samuel Rees

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Re: Why not Aux Controlled Subs?
« Reply #69 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.
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Re: Why not Aux Controlled Subs?
« Reply #69 on: January 18, 2014, 10:16:47 am »


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