QSC K-SUB using AUX 6 versus QSC built-in X-overs

[Harpman]

I have a pair of QSC K12's and 1 K-SUB that I use for our big band gigs (i.e. Bass/Drums).  I've been running it using the QSC X-over which has been working fine.  I would occasionally get low rumble from the vocal mics in the K-SUB, so I've decided to run the K-SUB separately through AUX 6. That way I only send what I want to send (i.e. Bass, Kick and Floor Tom).  The K-12's have a decent low frequency response for everything else.  Also on AUX 6, I turn off the PEQ and only use the GEQ.  I've set the EQ pretty much in the range of the published frequency response for the K-SUB (around 43 - 150Hz). I've attached a link to the image of the AUX 6 EQ. Would love to hear comments from others who have a QSC K-Series setup.

Like to screen shot: https://www.dropbox.com/s/rkftthl3ti08yoc/Aux%206%20EQ.PNG

[stevegarris]

I have a pair of QSC K12's and 1 K-SUB that I use for our big band gigs (i.e. Bass/Drums).  I've been running it using the QSC X-over which has been working fine.  I would occasionally get low rumble from the vocal mics in the K-SUB, so I've decided to run the K-SUB separately through AUX 6. That way I only send what I want to send (i.e. Bass, Kick and Floor Tom).  The K-12's have a decent low frequency response for everything else.  Also on AUX 6, I turn off the PEQ and only use the GEQ.  I've set the EQ pretty much in the range of the published frequency response for the K-SUB (around 43 - 150Hz). I've attached a link to the image of the AUX 6 EQ. Would love to hear comments from others who have a QSC K-Series setup.

Like to screen shot: https://www.dropbox.com/s/rkftthl3ti08yoc/Aux%206%20EQ.PNG

My experience has been that it sounds much better to use the board to create a sub mix, even without the output graphic EQ.
One of my best sounding setups has been my PRX615's over a clubs KW118's. To do this, I use the Left output to the subs and the Right output to the tops. I pan everything hard right except the kick and bass guitar. I do need to do a little filtering where they overlap. Seems to be around 180 hz.

[Greg C.]

Why are you using the graphic at all? It looks like you're trying to use it as a low pass filter which you don't need. the K-Sub has a built-in 100Hz low pass filter. Also, graphic EQs make very crappy crossovers. If you're ever forced to use one that way, you want all hard cuts past the "crossover frequency." The next question is, what are you doing to high pass the signal to the tops so they're not overlapping the subs too much? The K12s should be set to "EXT SUB" on the back which is a 100Hz high pass filter to match the sub.

[Greg C.]

I'll also add that if you need to EQ your sub(s) to say pull out a boomy frequency, the only type of EQ to use is a parametric EQ. The reason being that the bandwidth on a 1/3rd octave graphic is WAY too big. Subs cover less than 2 octaves of the audio range, so only a full parametric EQ with adjustable bandwidth/Q control can give you the precision needed to make the proper tweak. For instance on my subs, I only need a very tight -3dB notch at 50Hz to smooth them out. No way to attempt that on a graphic. To do so would mean killing a large swatch of frequencies in that area.

[Harpman]

Why are you using the graphic at all? It looks like you're trying to use it as a low pass filter which you don't need. the K-Sub has a built-in 100Hz low pass filter. Also, graphic EQs make very crappy crossovers. If you're ever forced to use one that way, you want all hard cuts past the "crossover frequency." The next question is, what are you doing to high pass the signal to the tops so they're not overlapping the subs too much? The K12s should be set to "EXT SUB" on the back which is a 100Hz high pass filter to match the sub.

Greg, I do set the K12's to "EXT SUB" as you mentioned.  So what you are saying in the first part of this post is to leave the PEQ/GEQ flat or disabled all together?  Sorry, didn't see you second post.  So leave the PEQ enabled and GEQ flat and only adjust PEQ if needed, correct? So in your situation, you notch -3db at 50Hz and leave everything else flat?

[Greg C.]

So leave the PEQ enabled and GEQ flat and only adjust PEQ if needed, correct? So in your situation, you notch -3db at 50Hz and leave everything else flat?

Correct, PEQ enabled if you need it. My subs are much different than yours. You may need no EQ at all on your subs. Mine have a sightly noticeable bump at 50Hz in the room I use them in that needs only a very small, tight notch to tame. Other than that, no other EQ applied to my subs.

[Harpman]

So leave the PEQ enabled and GEQ flat and only adjust PEQ if needed, correct? So in your situation, you notch -3db at 50Hz and leave everything else flat?

Correct, PEQ enabled if you need it. My subs are much different than yours. You may need no EQ at all on your subs. Mine have a sightly noticeable bump at 50Hz in the room I use them in that needs only a very small, tight notch to tame. Other than that, no other EQ applied to my subs.

Thanks Greg, appreciate your input. Played a little with it last night and it sounds really good now. Good separation.

[WK154]

Like you stated "it's working fine", so don't fix it in the crossover area. It sounds like the "rumble" in the vox channels need to be looked at, after all it's still rumble in the tops. Would be useful if the frequency of this is identified and fixed another way. SteveG method is handy since it doesn't require a layer change for control as the aux 6 method does. The only eq (parametric) would be to knock out room acoustic problems like Greg's 50 Hz standing wave. I can't buy that a mfg would produce a sub with that characteristic. Even this is limited as a solution. See http://www.sengpielaudio.com/calculator-roommodes.htm  .

[Greg C.]

The only eq (parametric) would be to knock out room acoustic problems like Greg's 50 Hz standing wave. I can't buy that a mfg would produce a sub with that characteristic.

If you're referring to my subs, the 50Hz cut is to correct the box itself rather than a room mode. I realize I miscommunicated that in my last post. My subs are Rat Sound dual 18s and the only processing they need is that tiny cut at 50Hz along with the low pass and limiter. I'd say though that such a small, relatively optional amount of EQ is a testament to how well designed those subs really are. I've used subs requiring several points of notching to tame them, and with these that one notch isn't essential for good fidelity.

[4mal]

Ext sub on the k series tops engages the HPF side of the crossover so...  Setting that on the tops, running the kick, bass and other stuff that needs the sub through your Aux mix and onto the Sub is a way to cut mic stand rumble, acoustic guitar boom, etc out of your system.  I find that I can get a fat punchy mix doing that.  Hte bass, kick, etc all goes into the main mix so it is represented in the tops as well and with exactly the same crossover impacts as though the tops were connected to the through on the sub.

Aux fed subs are one tool in the kit.  Like any other tool, it can be misapplied.  Ultimately your ears have to tell you that you have a good mix.  Do it wrong and you can certainly get some funky results...