Subwoofer crossover with full range mains

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CherylJosie

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I am mixing sound for a local band at their (infrequent) gigs.

The band is using the Mackie DL1608 mixer running Master Fader (actually an earlier version where the only available user manual is in the iPad app, but you get the idea) with SA1530z full range mains and SWA1801z subwoofers.

I plan on setting the downstream levels so that all instruments that use the subwoofers will be at 0dB on the aux fader because that keeps it mindlessly simple. I also plan on keeping the active speakers' input attenuators at 0dB because that also keeps it mindlessly simple.

The level balancing between mains and subs will happen only on the aux sub channel output fader that is ganged with the mains fader in a FOH master VCA.

I tried using the 120Hz 12dB/octave highpass in Master Fader to cross the active mains to the active subs at the subwoofers' built-in fixed frequency crossover, but two things happened. First, the guitars were not using the subwoofers, and they lost 80-120Hz frequency range. Second, the drummer who owns the equipment expressed his desire to keep using the mains full range because he feels he would get maximum power output (and I agree, with qualifications).

I worked up a compromise of a 6dB/octave 60Hz crossover implemented on the mains and subs output in highpass and lowpass filters tuned to 60Hz.

This should put approximately 3/4 of the power through the subwoofers at 30Hz, split the power evenly at 60Hz where the mains are near the LFE corner of their low frequency peak output, and put 3/4 of the power through the mains at 120Hz, except that at 120Hz the subwoofers will already be in their built-in crossover range and dropping out some as well as phase-shifted so there might be a dip in the combined response at 120Hz. The mains have a small peak between 105-130Hz though and that should help smooth out that range, with any residual frequency response aberrations fixed in the graphic.

There will be some vertical beaming due to the relative phase shift between drivers with a 6dB/octave crossover, but the mathematically summed signal of this 6dB/octave crossover is impulse-perfect and the imaging should be largely unaffected by some vertical beaming at such low frequencies, so I am fairly confident this solution will work out OK.

I have not tested this crossover configuration yet, but I have added it to Master Fader for the next gig.

I am new at this, and so far I have gotten little feedback as to the proper approach online. I had to come up with this solution on my own by reading manuals and applying my pre-existing electrical engineering skills.

Any suggestions?
 
You're overthinking this. Haven't we been through this before? Generally speaking, a person performing on stage has no business making important decisions about the front of house sound.

Simply doing a normal crossover arrangement on the whole 2-track mix would be a lot easier and leave you more headroom (your actual head, not the audio) to deal with more pressing problems at a live show (like dealing with stubborn, know-it-all drummers). Since you have a digital mixer you can likely set HPFs on channels to tailor them individually, largely removing the need for aux fed subs.

But if you must do aux fed subs perhaps a lower crossover frequency would be better, and it still requires high-passing the mains at the same frequency to prevent reproducing the same frequencies from two different sources that will have different phase responses regardless of what you do. That second point is non-negotiable.
 
I agree. You are overthinking it. Just cross over at 80hz with a 12db or 24db slope. A gentle slope will cause all sorts of phase stupidity and it will actually rob you of power. By not sending the full range speakers the sub frequencies, it frees up headroom to keep everything above 80hz clean and loud. By not sending anything above 80hz to the subs, you accomplish the same thing, as all the power will be used for the sub frequencies. The system will be stronger and more coherent this way.
 
And if you really want to get into things on that level, get SMAART and a reference mic, set the system up, and test it rather than guess.
 
I run a system exactly like this.

The front of house graphics on the full range: I slope the eq from about 100hz down to 0 at 20hz, you need to experiment with this both starting point and the shape of the curve some of the guys that use the system do a full cut from 100 hz down but I prefer a slope. If you do the old one two testing through a mic with the subs off it works for me, I hate reference mics, white noise and all that, you can tell if it's not right using your ears.

Then I have the subs set to a crossover point around 80 Hz.

I use a post fader Aux send to the subs (this by passes all the FOH EQ) I then balance the instruments going to the subs with the aux send. Usually Kick, Bass, Floor tom/low toms, sometimes Keys.

There is nothing below the 80hz (or even about 120hz) that guitars need to have, and especially vocals.

The full range set up like this sounds much cleaner as do the subs not having to filter out stuff they don't want via the crossover. Tell the drummer that doing it this way will actually get more power due to the system trying to reproduce frequencies in places they should not be, I.E 12" or 15" speakers trying to reproduce subs and subs trying to reproduce highs.

Alan.
 
An actual high pass filter on the mains would be better, but I guess cutting the graphic would be better than nothing. Definitely, cutting the lows from the mains lets them get louder. And it prevents LF cancellation between mains and subs which can reduce LF output. Running the mains full range actually reduces output.

The software I use doesn't do pink noise, it does a sweep. I also mostly depend on my ears, but there are times when measurement helps. The OP seems not do be doing either, just reading and thinking.

Some voices need 100Hz so I wouldn't assume you can high pass higher than that in every case. Usually the low cut I do to offset proximity effect helps reduce stage rumble well enough, but I'd avoid high passing too high just by default.
 
I use the graphic for HPF because the HPFs have different slopes depending on the maker, with the graphic you can adjust the slope and even out any crossover problems between HP filtering and the sub LP slope, just my thoughts.

I find very few singers live need any thing below 100hz, you could of course add a little sub send on vocalists you think need it, but I doubt it. I know what you are saying about sweeps, but I still believe that using your own voice and learning what works is a priceless tool in understanding audio. Funny when I am sound checking I pick out the frequencies with the CHECK ONE TWO, TESTING TESTING, and then change my voice so I am boosting the frequencies that I think are a problem, and cutting them on the EQ, gee I get some funny looks, but I also get a lot of compliments about the sound being good when the band kicks in. If the vocals sound good the rest will fall into place.


Alan.
 
Using your voice is fine. I wouldn't say don't do that. I don't use my voice, I use familiar recordings to set up systems. But measurement is also useful. I find it more effective than listening for fine adjustments like setting delays between bandpasses.
 
witzendoz said:
Funny when I am sound checking I pick out the frequencies with the CHECK ONE TWO, TESTING TESTING, and then change my voice so I am boosting the frequencies that I think are a problem, and cutting them on the EQ, gee I get some funny looks, but I also get a lot of compliments about the sound being good when the band kicks in. If the vocals sound good the rest will fall into place.
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I too endure curious looks when I'm making weird noises when finding the wayward frequencies . . . but it works for me.
 
The thing that smart systems do that you can't do by ear is fix the timing between the tops and subs. Once you do that, the system comes into focus and you don't have so many issues around the crossover frequency.

I was out of the live sound gig for a long time, when did everyone stop using proper crossovers? I still use a driverack for smaller systems. The big line arrays have a system to address each cabinet in the array, but that's a giant concert system.
 
I agree about a real crossover and my old large system had them, the DBX driverack is a great piece of gear. However what I suggested can work fine, and the aux to sub is a great option to have and you can't (I think) do this via a driverack.

Alan.
 
My Behringer DCX2496 has three inputs and six outputs, so it can do aux fed subs in one unit.
 
bouldersoundguy said:
My Behringer DCX2496 has three inputs and six outputs, so it can do aux fed subs in one unit.
Click to expand...

Look like a good piece of gear. If the OP can afford it get something like this. If not do it like I said.

By the way is the original OP still reading this LOL

Alan.
 
bouldersoundguy said:
An actual high pass filter on the mains would be better, but I guess cutting the graphic would be better than nothing. Definitely, cutting the lows from the mains lets them get louder. And it prevents LF cancellation between mains and subs which can reduce LF output. Running the mains full range actually reduces output.

The software I use doesn't do pink noise, it does a sweep. I also mostly depend on my ears, but there are times when measurement helps. The OP seems not do be doing either, just reading and thinking.

Some voices need 100Hz so I wouldn't assume you can high pass higher than that in every case. Usually the low cut I do to offset proximity effect helps reduce stage rumble well enough, but I'd avoid high passing too high just by default.
Click to expand...

yup, but you also have to know your speakers, for instance EAW hates 800 and 600, its in the design. I always ran my main EQ basically flat, and made my adjustments with the crossover and the strips, the main EQ was my last resort. On the main I cut to balance the system, IE the EAW freqs. And I had a list of songs I used to tune my rig with. tools are nice but I always used my ears last.
 
witzendoz said:
I agree about a real crossover and my old large system had them, the DBX driverack is a great piece of gear. However what I suggested can work fine, and the aux to sub is a great option to have and you can't (I think) do this via a driverack.

Alan.
Click to expand...

It depends on which version you get and if you are running mono or stereo. Even if you only have a stereo unit, you can still run the PA mono and use the other channel for the aux send.

I guess I do just use the filters on a digital console as a crossover sometimes. But never a graphic. But when I do that, it will be in a situation that is primarily a business meeting that has some entertainment, not an actual concert.
 
Remember I am only talking about filtering the subs out of the full range, the full range part of the system is capable of receiving the sub frequencies, I just remove them to make the system cleaner and to let the full range run easier. The sub side already has a crossover. I am therefore using the graphic as a filter not a crossover.

I also forgot to mention that on my own system (as opposed to the in house system I use) my power amps have inbuilt adjustable crossovers. The in house I use most of the time does not have this which is why I use the graphic, some operators don't use the graphic filtering on the full range but that up to them, each to their own.

Alan.

By the way I hope we have not bamboozled the OP.
 
Wow, lots of replies. I guess I found the right forum.

I will take these in order since the progression in the concerns seems logical as it unfolded naturally.

bouldersoundguy said:
You're overthinking this. Haven't we been through this before?
Click to expand...

Possibly on another forum? I had some delay getting into this one. Something about the membership having issues with new registrations.

Generally speaking, a person performing on stage has no business making important decisions about the front of house sound.
Click to expand...

It is OK, all good, we having fun.

Simply doing a normal crossover arrangement on the whole 2-track mix would be a lot easier and leave you more headroom (your actual head, not the audio) to deal with more pressing problems at a live show (like dealing with stubborn, know-it-all drummers).
Click to expand...

The drummer has reduced his average stage level considerably and expanded the dynamic range of his playing for a more engaging performance. We had some help from a pro resident sound engineer at one venue and that helped with the EQ as well as jumpstarting my learning curve. The band has been getting compliments on the improved sound. My biggest problem is still dealing with my own inexperience.

Since you have a digital mixer you can likely set HPFs on channels to tailor them individually, largely removing the need for aux fed subs.
Click to expand...

The per-input parametric EQ HPF is adjustable frequency 12dB/octave, so I am uncertain what good aux fed subs does for this setup.

When is aux fed appropriate/required/beneficial? No idea. Is that something typically reserved for higher power systems where the subwoofers are large enough to really muddy things up from nearfield? I have not noticed any problem from breath pops or footfalls with the aux fed sub. Everything sounds clean.
 
Farview said:
I agree. You are overthinking it. Just cross over at 80hz with a 12db or 24db slope. A gentle slope will cause all sorts of phase stupidity and it will actually rob you of power. By not sending the full range speakers the sub frequencies, it frees up headroom to keep everything above 80hz clean and loud. By not sending anything above 80hz to the subs, you accomplish the same thing, as all the power will be used for the sub frequencies. The system will be stronger and more coherent this way.
Click to expand...

I originally suggested 80Hz to a resident pro sound engineer at one of the larger venues we played, and he indicated that was low, so I used 120Hz. The sound was good, but I mistakenly added 12dB/octave LPF on the aux (sub) output (so the combination of internal and external could have been 24dB/octave) while only using 12dB/octave HPF on the mains and I did not even investigate the phase switch on the subs.

Linkwitz-Riley? Presumably that is the type of crossover built into the subwoofer. I doubt the HPF/LPF in the DL1608 is cascaded though? Or is it? If not, then any crossover in the mixer may have a slight bump in response at crossover. ???
 
Aux fed subs is a really cool idea that I never got to implement before I had to sell off my PA gear due to physical limitations (just not willing/able to haul that much weight two or three times in one day). It keeps vocal/guitar/etc. mics from adding unwanted LF to the room. Analog mixers with fixed HPF filters really could benefit from that, but digital mixers give you the flexibility to HPF each channel as needed, so the benefit is much less.

If vocal/guitar/etc. mics are adding too much rumble to the sound even when you high pass them, maybe aux fed subs would be the solution. But that means spending more time and attention, using up an aux send, more processing etc. I always found those to be in short supply when setting up for a show. The simplest good solution was the best solution as it got things going faster and with less strain on limited resources. In a big show with a big system and large crew it's a minor thing to configure aux fed subs, but if you have to do it all you need to prioritize.

Whether you do aux fed subs or a conventional crossover arrangement, high passing the tops is essential for two reasons. One, they'll get louder with less strain, and so sound better. Two, they will interfere less with the subs, and so cause less loss where they overlap. Different kinds of speakers have different phase response. Even if you get them in phase at one frequency they will be out of phase at other frequencies. When they are out of phase (by more than 90°) they cancel to some degree, causing a loss of level and clarity compared to having just one speaker reproducing that frequency. If you want more low end power then add more subs of the same type.

I would suggest setting the system up and testing it when you don't have a show to put on, especially if you can do it outdoors away from buildings. Then you can see what it sounds like without a room's effect. Then you'll have a baseline for comparison. Each room will be different. You can start to sort out what changes need to be made for each particular space. Generally you can do some basic overall eq to adapt to a given room, typically cuts at certain frequencies that resonate due to certain room sizes and shapes. With a digital system you can save those settings for recall, giving you a head start on tuning the system next time you're at that venue.
 
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