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Author Topic: Why not Aux Controlled Subs?  (Read 7685 times)

TJ (Tom) Cornish

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Re: Why not Aux Controlled Subs?
« Reply #20 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.
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Brian Charbobs

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Re: Why not Aux Controlled Subs?
« Reply #21 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.
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Samuel Rees

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Re: Why not Aux Controlled Subs?
« Reply #22 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.
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David Sturzenbecher

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Re: Why not Aux Controlled Subs?
« Reply #23 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.
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John Penkala

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Re: Why not Aux Controlled Subs?
« Reply #24 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
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Mac Kerr

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Re: Why not Aux Controlled Subs?
« Reply #25 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
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David Sturzenbecher

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Why not Aux Controlled Subs?
« Reply #26 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.


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Mac Kerr

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Re: Why not Aux Controlled Subs?
« Reply #27 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
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David Sturzenbecher

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Re: Why not Aux Controlled Subs?
« Reply #28 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.
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Malcolm Macgregor

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Re: Why not Aux Controlled Subs?
« Reply #29 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.
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