Crossover with mono subs and LCR tops

[Anonymous067]

I'm beating my head on my desk right now trying to figure out a low budget (I know I know...bad to say) way of solving this problem.

Current setup-a LCR (true) system, with biamped Center and one amp channel per LR.

The current setup has DSP's that I assume roll off all lows (behind security grates, rather NOT deal with these if possible...). JBL DSC260.

I want to run a few subs off the matrix sends of my board, not through the mains. I have my reasons.

My question is what is a good way to make some type of crossover work without putting a second xover on all four output channels?
See my problem?

The place I'm getting the subs from is including a two channel crossover, but at this point, I'm thinking my best bet is to use that crossover just on my subs, and setting the house dsp xovers to the same freqs just passing the opposite end of the spectrum (just the highs)...

The biggest thing I don't wanna do is throw my subs off my mains...
?????
help?

 

[rwhealey]

It would probably be easiest to hi-pass the LRC speakers at the DSP and use the analog crossover for your sub.

If you can't get to the DSP and you only have a 2 in 4 out crossover, I would leave the LRC alone and go [matrix-crossover-amp-sub]. You'll be overlapping the sub with the mains and that could have unpredictable results, but I just don't see enough channels available.

If you can run the show in mono, I would just go [C Out-crossover ch.1 -(3 way Y cable)-DSP-amps-LCR speakers] and [matrix-crossover ch.2-amp-sub].

 

[Anonymous067]

Ugh...good point about running a mono show...I really don't WANT to...but it certainly is an easy option out of this mess...

I could try overlapping freqs too and see how bad it is, but I really do need a backup plan in case that sounds horrible.

 

[TimmyP1955]

You are describing an "aux fed subs" configuration (Live Sound: In-Depth: The Aux-Fed Subwoofer Technique Explained - Pro Sound Web).

It is best if the tops are properly high-passed (customarily between 80 and 100). If not, the system can still work well provided that the sub low pass is set appropriately (set to "match" the natural rolloff of the tops).

Don't use a matrix, use an aux (or one of a pair of submasters). You don't want to run everything into the subs, only those things that need low end (bass, kick, toms, maybe keys).

 

[Anonymous067]

Well the reason I wanted to use Matrix sends was because I can just pull groups and throw in the matrix for the sub...and patching would be a whole lot easier...

Any specific reason not to use matrices and use auxs?

To elaborate...
I see the advantage, but the way I plan on setting up my groups...all that will go to the subs is groups that will help the LF image. I double my instrument groups, and only send instruments with a need for the subs reinforcement to the second set of instrument groups. That group then mixes with the playback groups in a matrix and goes to the sub.

 

[The_Guest]

Well the reason I wanted to use Matrix sends was because I can just pull groups and throw in the matrix for the sub...and patching would be a whole lot easier...

Any specific reason not to use matrices and use auxs?

To elaborate...
I see the advantage, but the way I plan on setting up my groups...all that will go to the subs is groups that will help the LF image. I double my instrument groups, and only send instruments with a need for the subs reinforcement to the second set of instrument groups. That group then mixes with the playback groups in a matrix and goes to the sub.

The issue isn't just being able to select what goes to your subs, but also how much.

The main advantage to feeding the subs through the auxs is the ability to individually throttle the amount each channel goes to the subs. In other words, think of it super discrete low-end eq knob. I would imagine this is particularly useful in your situation where you have an installation DSP for house system you would prefer not to fuss with as little as possible (which I totally understand). The aux-fed method enables you more control so that the C subs and extra LR subs can play nicely together. Because you're not using a singe unified DSP for everything, tuning the two sets of subs can be tricky. Even after EQ'ing the extra subs to match the C subs, even the slightest volume or low-end eq changes on the FOH console could cause the two to sound different. In other words, just because you get everything to sound good together at one combination of volumes/eq-settings, doesn't necessarily mean things will remain consistent throughout different combinations. Why you ask? Unless your hardware is perfectly matched (identical DSPs) and the room consistently resonates bass from the subs regardless of placement, prodigious tuning and luck will be necessary.

For example, if you adjust a channel's parametric bass eq on your FOH console you'll be adjusting the bass of the aggregate mix (both subs). What if an instruments low end sounds muddy no matter how you eq it at FOH? Chances are, the two sets of subs aren't working together nicely. You could either choose to route the low end to just the C subs or you could find a unique blend by adjusting the amount of LR sub feed through the aux.

Its fine to feed it to the matrix, just as long as you can feed your auxs to the matrix.

 

[museav]

I have to disagree a bit and feel that the main logic behind aux fed subs is to control what sources go to the subs rather than to control level. Two reasons for this. The first is that I believe the primary goal of having a separate sub mix with live sound is to limit what goes to the subs. For example, if the vocal mics are not routed to the subs then any low frequency sounds those mics pick up also won't go there, so less muddying of kick, bass, etc. Also less pickup of extraneous noise. The second reason is that as you adjust the level of the subs you are also adjusting the related system crossover point. Turn the sub level up without also turning up the associated high pass signal(s) and the acoustic crossover point shifts up, turn the sub level down relative to the rest of the signal and the crossover point shifts down. So when you adjust just the sub feed level you are not only affecting the level but also the sub's crossover point. Not necessarily something you want to be doing all the time.

Another possibility. You have a true LCR system with an existing processor that you would prefer to not have to reprogram. How many of the sources that you would include in the sub mix would have much, if any, center channel assignment? Would it be feasible to treat those sources more like stereo with hard left and right panning? What I'm thinking is that if that is possible the you could insert the analog crossover on the left and right console outputs, running the HF outputs of the crossover to the left and right mains and the LF outputs to the subs. You might have to play with the crossover settings a bit to best match the processing already in the JBL processor. Alternatively, you could do as noted and simply 'Y' the left and right console outputs to the crossover for the subs and the JBL processor for the mains.

 

[Anonymous067]

Another possibility. You have a true LCR system with an existing processor that you would prefer to not have to reprogram. How many of the sources that you would include in the sub mix would have much, if any, center channel assignment? Would it be feasible to treat those sources more like stereo with hard left and right panning? What I'm thinking is that if that is possible the you could insert the analog crossover on the left and right console outputs, running the HF outputs of the crossover to the left and right mains and the LF outputs to the subs. You might have to play with the crossover settings a bit to best match the processing already in the JBL processor. Alternatively, you could do as noted and simply 'Y' the left and right console outputs to the crossover for the subs and the JBL processor for the mains.

That gave me a great idea!!! I looked at my plot, and all I'll probably run to center is vocals and lavs, neither of which will be routed to the subs.

Crossover on LR and I might even bypass the LR DSP.... all it has is EQ and Limiting, plus crossover. The crossover will already be taken care of, and the EQ I really don't care about... (I will look however at how significant it is...), and limiting, well, I have a full meter bridge, I'll make sure nothing clips at the output.

How does that plan sound?

 

[Anonymous067]

Brain fart at 11 PM...I have two channels of compression...

LR and subs is three. Darn it. For a little while I thought I had it....

Looks like I'll be going soon to buy another crossover...

 

[TimmyP1955]

Well the reason I wanted to use Matrix sends was because I can just pull groups and throw in the matrix for the sub...and patching would be a whole lot easier...

Any specific reason not to use matrices and use auxs?

To elaborate...
I see the advantage, but the way I plan on setting up my groups...all that will go to the subs is groups that will help the LF image. I double my instrument groups, and only send instruments with a need for the subs reinforcement to the second set of instrument groups. That group then mixes with the playback groups in a matrix and goes to the sub.

Ah. So for example:

Drums assigned to groups 1 and 2, snare, hat, overheads panned to 1, kick & toms panned to 2, 2 fed to the subs matrix. If you need more drums, you turn up 1 and 2, and the subs level follows. Makes sense. Carry on mixing