Aux feed subs?

[Guy Graham]

Re: Aux feed subs?

When using aux-fed subs, whether as an addition to a full-range system or as the only sub-bass reinforcement in that passband, do you have to ensure all the processing used for crossover across the whole system is the same - eg proprietary L'Acoustics LA series, DBX, XTA or LG PLM Lake and so forth.

Or can a different brand of processor be used for the subs, as long as matching appropriate types of filter (eg LR 24dB at X freq slope) are used in line with the existing processing being used for the main array such subs might be added to?

My thoughts are instinctively that the same type of processor should be used across the whole system, since measurements have shown that the same type crossover slope from different manufacturers are not always measured identically. My query specifically is concerned with how folks such as Evan K. deal with this issue, when bringing extra subs to be fed from an aux to add to an existing system in a hypothetical venue ... in such circumstances is it

a) essential to match your aux subs' processing to the rig they are being added to

b) 'ideal' but not essential

c) can different processors be mixed without issue, as long as crossover slopes and types are matched?

 

[BJ James]

Re: Aux feed subs?

d) match the DSP to your boxes.
I'd assume anyone bringing in extra boxes to supplement an installed system is going to bring their own DSP for them as well.

 

[Guy Graham]

Re: Aux feed subs?

d) match the DSP to your boxes.
I'd assume anyone bringing in extra boxes to supplement an installed system is going to bring their own DSP for them as well.

When you say "match the DSP to your boxes" do you mean matched to the sub boxes being added, or to the boxes these hypothetical subs are being added to?

Apologies if I wasn't clear - I know some type of DSP is required (both for the aux fed subs and the main house system in my hypothetical example) and took it as read that there would already be processing both which matches the boxes being brought in for aux fed subs, and correct/adaquate processing for all other loudspeakers in this scenario.

My query was along the lines of how closely the processing to be used for these extra boxes needs to match, or ideally should be the same brand and flavour as that already in use with the system that is being supplemented with the extra subs. Or can differing brands be used alongside each other, with no detriment to the sound quality, phase response and other key alignment parameters?

 

[Jason Phair]

Re: Aux feed subs?

I've heard the "acoustical crossover" argument from my friend Gordon several times over the years, and from a few others as well (though none seem to be as adamant and passionate as he is!). I follow the physics, and it all makes sense. But here's the question that's always seemed to have a fairly straight-forward answer to me, but I'll pose it for those of you who are way the hell smarter than I am to answer for me:

I generally do my alignment off an oscillator, and by ear. This oscillator is either bussed to the Sub Aux and the L/R, or it's a channel that goes to each. I don't change the master levels of either of these busses at this point. So, since I've done my alignment with those levels at where they are going to be, the alignment of the system remains appropriate, right?

Follow up question to that: You're not playing pink noise or sine tones all night, you're playing music. So, following the above theory, you'd have to set all your sub send levels, and align based on THAT program material, and then not be able to change sub level on any of the individual channels without throwing JUST THAT CHANNEL out of phase between subs and mains.


End Reality: I know there are plenty of compromises in an Aux-fed Sub world. But there are also plenty just given the fact that I generally fly my tops and have my subs on the ground. Also, the fact that I'm often in a big giant ellipse with 2 focal points, one of which is generally where they stick the stage. I have decided I'm okay with it. (besides, I'm generally providing for incoming engineers, and if they want it on an aux, they'll get it that way).

 

[Silas Pradetto]

Re: Aux feed subs?

I've heard the "acoustical crossover" argument from my friend Gordon several times over the years, and from a few others as well (though none seem to be as adamant and passionate as he is!). I follow the physics, and it all makes sense. But here's the question that's always seemed to have a fairly straight-forward answer to me, but I'll pose it for those of you who are way the hell smarter than I am to answer for me:

I generally do my alignment off an oscillator, and by ear. This oscillator is either bussed to the Sub Aux and the L/R, or it's a channel that goes to each. I don't change the master levels of either of these busses at this point. So, since I've done my alignment with those levels at where they are going to be, the alignment of the system remains appropriate, right?

Follow up question to that: You're not playing pink noise or sine tones all night, you're playing music. So, following the above theory, you'd have to set all your sub send levels, and align based on THAT program material, and then not be able to change sub level on any of the individual channels without throwing JUST THAT CHANNEL out of phase between subs and mains.


End Reality: I know there are plenty of compromises in an Aux-fed Sub world. But there are also plenty just given the fact that I generally fly my tops and have my subs on the ground. Also, the fact that I'm often in a big giant ellipse with 2 focal points, one of which is generally where they stick the stage. I have decided I'm okay with it. (besides, I'm generally providing for incoming engineers, and if they want it on an aux, they'll get it that way).

Summary: everything is a compromise. Getting it the best you can with the tools you have is what makes for a better show than the guys that just don't care.

 

[BJ James]

Re: Aux feed subs?

DSP (and amps) to match the boxes you're bringing in, regardless of the make of the house system. Then use SMAART or similar to align with existing subs.

 

[harrybrilljr]

Re: Aux feed subs?

Guy, when you use a matched system the subs and the mains are typically tweaked at the factory to play nice with each other. Straight delay is all that is needed to get them back to alignment. WHen mixing and matching, regardless of whether you use the matching DSP or not you will not have a matched set and will need to tweak to get things together.

Jason, you seem to think if you use music the system will have a different transfer function than if you used noise. It won't. That's why we can use music to measure with Smaart. If you drive the subs from an Aux you will have an inaccurate transfer function once you have built the mix. This is because some instruments that are in the reference will not be coming out of the subs. I want to make sure it's clear that using a sine wave will not work with Smaart. That's an ear thing. You can use swept sine with lots of averaging, but not just an individual tone. If you are manually sweeping your oscillator back and forth and listening to the interaction between the sub and main, that might work great. Your ear/brain is in charge (as it always should be). Finally, not that it matters, but pink noise represents music quite well as far as the system is concerned.

I've heard the "acoustical crossover" argument from my friend Gordon several times over the years, and from a few others as well (though none seem to be as adamant and passionate as he is!). I follow the physics, and it all makes sense. But here's the question that's always seemed to have a fairly straight-forward answer to me, but I'll pose it for those of you who are way the hell smarter than I am to answer for me:

I generally do my alignment off an oscillator, and by ear. This oscillator is either bussed to the Sub Aux and the L/R, or it's a channel that goes to each. I don't change the master levels of either of these busses at this point. So, since I've done my alignment with those levels at where they are going to be, the alignment of the system remains appropriate, right?

Follow up question to that: You're not playing pink noise or sine tones all night, you're playing music. So, following the above theory, you'd have to set all your sub send levels, and align based on THAT program material, and then not be able to change sub level on any of the individual channels without throwing JUST THAT CHANNEL out of phase between subs and mains.


End Reality: I know there are plenty of compromises in an Aux-fed Sub world. But there are also plenty just given the fact that I generally fly my tops and have my subs on the ground. Also, the fact that I'm often in a big giant ellipse with 2 focal points, one of which is generally where they stick the stage. I have decided I'm okay with it. (besides, I'm generally providing for incoming engineers, and if they want it on an aux, they'll get it that way).

 

[Bennett Prescott]

Re: Aux feed subs?

I just don't understand not using measurement. Everything else is so complicated and gives so little information. You need to use it to set your sub delay no matter what, and it makes checking your alignment vis a vis HPF / LPF trivial. Why wouldn't you?

 

[harrybrilljr]

Re: Aux feed subs?

I just don't understand not using measurement. Everything else is so complicated and gives so little information. You need to use it to set your sub delay no matter what, and it makes checking your alignment vis a vis HPF / LPF trivial. Why wouldn't you?

A lot of folks just don't believe they can afford the gear, the training, or just don't want to be bothered with the long learning curve. Some don't believe they should have to provide the gear and the management isn't providing it so there it is.

 

[Kip Conner]

Re: Aux feed subs?

It sure is amazing how quickly someone like that changes their tune (no pun intended) once they've seen a FFT in action. What I come across are engineers who have no idea what that window on the top of the TF is and with very little explanation guys get excited that this is something that they might be able to comprehend.

What is truly amazing is the number of guys out there that have never even seen one, A FFT that is.

 

[Tim McCulloch]

Re: Aux feed subs?

It sure is amazing how quickly someone like that changes their tune (no pun intended) once they've seen a FFT in action. What I come across are engineers who have no idea what that window on the top of the TF is and with very little explanation guys get excited that this is something that they might be able to comprehend.

What is truly amazing is the number of guys out there that have never even seen one, A FFT that is.

What is amazing to me are the number of folks that will buy a license and never use it for more than RTA. The mental block seems to be understanding how PHASE works, and that everything audio is centered around TIME. Once that barrier is breached appreciation for the dual channel FFT begins.

 

[Bennett Prescott]

Re: Aux feed subs?

A lot of folks just don't believe they can afford the gear, the training, or just don't want to be bothered with the long learning curve. Some don't believe they should have to provide the gear and the management isn't providing it so there it is.

It can't be any more difficult than trying to bullseye alignment using an SPL meter and fixed frequencies! That already indicates a good knowledge of the scope of the problem.

 

[Ivan Beaver]

Re: Aux feed subs?

I just don't understand not using measurement. Everything else is so complicated and gives so little information. You need to use it to set your sub delay no matter what, and it makes checking your alignment vis a vis HPF / LPF trivial. Why wouldn't you?

Because many people want a nice-simple-one size fits all set of numbers.

Why bother checking when you can just "believe" what is happening.

I hear people all the time make comments that simply aren't true and can't happen. Yet they hear this crap spewed from others mouths and repeat it as it it were gospel. Yet they have no idea what it means-how it works or the end result-but "so and so" said it-so it MUST be true.

HOW ABOUT actually measuring it yourself????????????? Now THAT is a concept that VERY FEW people in audio actually do-and the manufacturers know it.