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[Mac Kerr]

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

[David Sturzenbecher]

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. 

[Roland Clarke]

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.

[Mac Kerr]

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

[Bob Leonard]

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?

[John Chiara]

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?

[Bob Leonard]

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.

[Jamin Lynch]

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.

[Samuel Rees]

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.

[Malcolm Macgregor]

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)

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