[RAILhead]

Hey all

I have some questions about setting up a PA rig, and I have some specific questions that I'm not able to find answers to online -- so I thought I'd bounce them off you all to see if you know the details I'm trying to figure out. Okay, here's what I'm thinking (and this will probably be a LONG post)...

The setup would be:

1. 1 mains amp (Crown XLS 802)
2. 1 monitor amp (Crown XLS 202)
3. 1 sub amp (Crown XLS 802)
4. 1 crossover (dbx 223XL)
5. An EQ (but that doesn't factor into my questions)
6. 4 8-ohm speakers
7. 2 8-ohm sub speakers

From the desk, I'll have channels 1 & 2 which will go into the crossover channels 1&2. Here I'll split to my subs from the crossover LOW output, which will be 1 XLR to the sub amp -- and here's where I start getting confused. Which sub amp INPUT do I go into? Is this where I use the "bridge mono" mode of the amp? Or, do I just pick a channel and go with it, knowing I'll be totally wasting a channel on the amp?

The same thing for the mains. Do I go from the crossover's MID to say, channel 1 of the mains amp -- and go from the crossover's HIGH to channel 2 of the mains amp? THEN I'll know that channel 1 is for my mids, and channel 2 for my highs? That sounds great, and I guess I'd just take the channel 1&2 speakon outputs over to the speakon inputs of each speaker pair master, and hookup the secondary speakers in parallel for 4-ohms...?

If the above is correct...

I'll have 2 subs from 1 channel, in parallel for 4-ohms, from the Sub amp. I'll also have 2 HIGH speakers in parallel at 4-ohms (from channel 2 of the mains amp), and 2 MID speakers in parallel at 4-ohms (from channel 1 of the mains amp).

Does that sound right?

TIA,
Maury

[Doofy]

I think you're overthinking it.

By the looks of the back panel of the DBX, it's either stereo two-way or mono three-way.

Since we're not communists (and because you're using two outputs from your desk), I'll assume that we're going stereo. So it's a simple case of both central buttons on the back of the DBX left out and as such:

Desk L -> DBX Input 1.
Desk R -> DBX input 2.
DBX output High 1 -> Crown (main) 1 -> left main stack.
DBX output High 2 -> Crown (main) 2 -> right main stack.
DBX output Low 1 -> Crown (sub) 1 -> left sub.
DBX output Low 2 -> Crown (sub) 2 -> right sub.

It looks like you're trying to use stereo out of the desk and then go three-way. You'd need two DBXs for that, I think.

I'd watch the amp levels. 4 ohm (2x8 parallel) mains may well overwhelm 8 ohm subs if driven off the same amp model.

Not sure where the monitor amp is in all this.
Of course, this should take its input from a pre-fade aux on the desk (in bridged mono for one mix) or from two pre-fade auxes (to drive two separate mixes). You don't mention what this will be driving. Wedges?

[RAILhead]

Well, in this setup, I will be going mono -- so I don't have to use both desk channels.

In this case, is my original post accurate?

As for ohms, 2 8-ohm subs down to 4 is a problem? You think it's better to maintain the sub's stock ohms?

[Doofy]

Originally Posted by RAILhead 

Well, in this setup, I will be going mono -- so I don't have to use both desk channels.

In this case, is my original post accurate?

Yep, sounds right. Except the bit about using the channel 2 input on the DBX. As you'll see on the back panel (lower labels), in mono mode it's unused.

Go bridged mono on the sub (it's usually input "1" which is the input for bridge mode. As usual, check with the manual). Dual mono (not bridged) on the other amp, one channel for the mids and one for the highs.

Originally Posted by RAILhead 

As for ohms, 2 8-ohm subs down to 4 is a problem? You think it's better to maintain the sub's stock ohms?

Narh, if you're going mono it'll be OK. I was just worrying that in the stereo setup I popped in up there, the main stacks (4 ohms per side) would be pulling much more juice than the subs (at 8 ohms per side). As you know, ideally that should be the other way around since bass needs huge amounts of juice to keep up. But since you'll be running the sub amp in bridged mono, this won't be a problem since there'll be huge power on tap.

So yep, it's right. Just dump that cable from desk 2 to DBX 2.

HTH.

[Doofy]

Dang RAIL, I've just read the amp's manual. Won't do bridge into 4 ohms.
So I think you'll have to use the sub amp in stereo and waste a channel.

[RAILhead]

Okay, so screw the whole mono thing, and let's do stereo...

Fist off, looking here XLS Series shows all the amps will run at 4-ohm...?

Anyway, tell me if this is correct...

Desk channel 1 > dbx Channel 1 > dbx channel 1 high > mains amp channel 1 **AND** dbx channel 1 low > sub amp channel 1
Desk channel 2 > dbx Channel 2 > dbx channel 2 high > mains amp channel 2 **AND** dbx channel 2 low > sub amp channel 2

I've been looking at 8-ohm speakers so that I could parallel them down to 4-ohm and get more wattage out of the amps (800 watts per channel compared to 500 watts per channel). To do stereo, I'd need to run left and right directly out of the amp, which would be 8-ohms per speaker -- unless I just bought 4-ohm speakers. My original plan was to hook them up in parallel, but I don't see any way to do that with the above chain. Right?

[Doofy]

Originally Posted by RAILhead 

Fist off, looking here XLS Series shows all the amps will run at 4-ohm...?

Yep, but only when run in stereo (two channel) mode. When run in bridged mono, they won't (if I'm reading the manual correctly - I think there's a thermal cutout which would be forever tripping if you tried to run 4 ohm bridged). Only the fat one appears to be able to do 4 ohm bridged, but I'd love to see the subs which would handle 5,000w.

Originally Posted by RAILhead 

Anyway, tell me if this is correct...

Desk channel 1 > dbx Channel 1 > dbx channel 1 high > mains amp channel 1 **AND** dbx channel 1 low > sub amp channel 1
Desk channel 2 > dbx Channel 2 > dbx channel 2 high > mains amp channel 2 **AND** dbx channel 2 low > sub amp channel 2

Yup.

Originally Posted by RAILhead 

I've been looking at 8-ohm speakers so that I could parallel them down to 4-ohm and get more wattage out of the amps (800 watts per channel compared to 500 watts per channel). To do stereo, I'd need to run left and right directly out of the amp, which would be 8-ohms per speaker -- unless I just bought 4-ohm speakers. My original plan was to hook them up in parallel, but I don't see any way to do that with the above chain. Right?

A lot of cabs have parallel speakons on the back of them, so literally:
Amp -> cab 1 (8 ohm) -> cab 2 (8 ohm) == 4 ohm.

If you're buying from scratch (which it would appear you are), then I'd be looking at the following:

Main amp.
2 x 8 ohm main speakers.
Sub amp.
2 x 4 ohm sub speakers or 4 x 8 ohm sub speakers.

That way, the subs will be pulling 800w while the mains will be pulling 500w. Depending on cab and speaker efficiency, that will probably give you a better balance.

Although you could save yourself a whole heap of bother by just buying some active jobbies. That way it's just:
Desk -> Speaker.
Or, if you grab the subwoofers:
Desk -> Sub -> Speaker.

[Railroader]

Get a room you two!

[RAILhead]

Originally Posted by Doofy 

A lot of cabs have parallel speakons on the back of them, so literally:
Amp -> cab 1 (8 ohm) -> cab 2 (8 ohm) == 4 ohm.

If you're buying from scratch (which it would appear you are), then I'd be looking at the following:

Main amp.
2 x 8 ohm main speakers.
Sub amp.
2 x 4 ohm sub speakers or 4 x 8 ohm sub speakers.

That way, the subs will be pulling 800w while the mains will be pulling 500w. Depending on cab and speaker efficiency, that will probably give you a better balance.

Gotcha. So everything would be wired in stereo, not parallel. And if I did that -- and decided to add 2 more mains later -- I'd have that much more power out of the mains since I'd have 4 mains at 4-ohms.

[RAILhead]

Hm. Having a hard time finding 4-ohms subs... Plenty of 8-ohm, though.

[Doofy]

Originally Posted by RAILhead 

Gotcha. So everything would be wired in stereo, not parallel. And if I did that -- and decided to add 2 more mains later -- I'd have that much more power out of the mains since I'd have 4 mains at 4-ohms.

Yup.

Quick and dirty:



Dashed lines are parallel connects out of the speaker.

[RAILhead]

Noice!

Thanks for helping me figure this crap out!

[Doofy]

Nay worries.

[RAILhead]

I guess the DBX having "high" and "low" outputs for each channel really makes no difference as far as going to the mains or sub amps, right? Meaning, the mains amp couldn't give a rat's whether or not its channel 1 or 2 is the crossover's high or low, right?

[Doofy]

Originally Posted by RAILhead 

I guess the DBX having "high" and "low" outputs for each channel really makes no difference as far as going to the mains or sub amps, right? Meaning, the mains amp couldn't give a rat's whether or not its channel 1 or 2 is the crossover's high or low, right?

As far as I'm aware, there shouldn't be any issue - amps don't care.

[RAILhead]

Okay, so here's another question. If you look at amps like the Crown XLS 5000, which is rated for 1100 watts per channel at 8-ohms, or 1800 watts at four -- how in Hades do you NOT blow speakers...? Are people with amps like this using speakers you just can't normally find at retailers? I have yet to see ANYTHING with an RMS rating of 1100 watts, much less 1800! Peak, sure -- but not RMS.

How in the crap are they using such powerful amps?

[RAILhead]

Belay that - sort of. I see where JBL makes a dual 15 that's 1200 watts rms, but it's 4-ohm. That still ends up being less than the watt power of the crown 5000, so I don't see how that could work, either.

[Doofy]

Well... That dual 15 JBL will prolly be two 8 ohm drivers wired in parallel. Get in there with the soldering iron and wire it to series, that's 16 ohm. Parallel it with another cab wired the same and you're back down to 8 ohms.

But it's all a bit silly - when all's said and done a lower powered amp running through the right enclosure will do a lot more damage to the audience than a huge amp through crappy cabs. The loudest thing I ever heard in my life was a 25-watt amp running into some horn-loaded bass bins - front and centre at a Motorhead gig doesn't even come close. IIRC, normal cabs are only about 2-3% efficient, whereas horn loaded gets over 50%.

[RAILhead]

Totally. Our issue is getting enough power for outdoor shows with the crappy amp my buddy has. I'm thinking I may just buy my own stuff, build my own rig, and get enough to be able to cover 100 feet (plus) of audience while playing in the center of a field. That'd be around 800 watts per cab with 10dB of clipping factored in. I'm liking the JBL SRX715s for mains, and the SRX718S for subs.

[Doofy]

Can't go far wrong with a bit of JBL.