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I have an opportunity to buy a JBL JRX118 powered sub at $400. I would be using it with some passive tops out of a powered mixer -- is that possible/desirable?

Come to think of it, I think I might need a course in crossovers. I understand the concept of breaking the signal into frequency bands, but I don't really understand where I put it in the chain. Would it normally be:

     Mixer  ---> Crossover --> Amp --> Tops
                                            ---> Powered Sub

Or is it:

      Mixer --> Amp --> Crossover --> Tops
                                                       --> Sub

I'm not sure if he's using both sides of the amp for frontals. I didn't know they had a amp insert, but i just took a look at the Behringer site, and a nice L & R, that wouldn't be to bad then. Just think how nice it would have been just to have put a filter on the mono out.  Do you already have a crossover?

Actually if that's the mixer, you could actually hook up a crossover to it.  It has a power amp insert, which is basically like a send/return loop.  Use the main stereo line out to the crossover, then the high out of the crossover to the power amp insert & run the mixer internal amp to the top cabs, then the low (sub) out of the crossover to the sub input.  
The sub actually has a built in high pass so it will act as a pass through crossover as well.  So the main stereo line out to the sub  input a & input b.  Set the  outputs a&b to HPF (high pass filter), now the output a & output b of the sub to the power amp insert l & r on the mixer.  Then mixer internal amp  speaker outputs to the top speakers.

re you using any other external amps? I'm not sure how you run your power now, just for frontals, for frontals and a monitor, in stereo, dual mono?

If I knew how you were using it now, it would be easier to figure out what you need to do.

I use it in stereo, mostly. I sometimes use it in mono/monitor mode with active tops, while I run a monitor on output B of the powered mixer. Usually though, I use stereo, as I have smaller gigs with well-localized audience.

I have a separate small power amp for the monitor.

My lineup of available options is:

        PMH3000 and either MTX 12" or Behringer 15" mains
        Samson 120W amp (bridged) with Kustom 10" monitor speaker
        B212A active 12" speakers

I am looking to add the JBL sub and a crossover.

I also have my portable setup I can carry with me in the car, the PMH518 mono powered mixer with Kustom 10" speakers. Cheap, but packs quite a bit of punch for a little < $300 setup. (I use this as a portable PA for speaking engagements as well.) The PMH518 also has an amp insert, so I can use it for a monitor amp if necessary.

Well, that does open up your options a bit. If you already have powered tops available, you could use your powered 12's as you won't be depending on them to reproduce bottom any longer. The JRX118SP has a built in High pass filter in it with through jacks, so If i'm not mistaken you could just use your line outs into the JBL then a line from the JBL to your B212A's. Then you could just use your internal amp on the PMH to run just monitors. There are actually a few alternatives you could do with the gear you have available. Do you already have an electronic cross over?

Do you already have an electronic cross over?

Yes, it has an amp insert. I guess I didn't realize that I could use the mixer portion at the same time I used the other.

So it becomes:

                                                   --> L/R to Mixer Amp Insert --> Tops
        Pwr Mixer --> L/R to Crossover
                                                   --> Mono to Powered sub

New postPosted: Today at 9:47 am  
Re: JBL JRX118 powered sub
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mckyj57 @ Fri Oct 05, 2007 12:54 am wrote:
Lonman @ Thu Oct 04, 2007 5:32 pm wrote:
Actually if that's the mixer, you could actually hook up a crossover to it.  It has a power amp insert, which is basically like a send/return loop.  Use the main stereo line out to the crossover, then the high out of the crossover to the power amp insert & run the mixer internal amp to the top cabs, then the low (sub) out of the crossover to the sub input.  
The sub actually has a built in high pass so it will act as a pass through crossover as well.  So the main stereo line out to the sub  input a & input b.  Set the  outputs a&b to HPF (high pass filter), now the output a & output b of the sub to the power amp insert l & r on the mixer.  Then mixer internal amp  speaker outputs to the top speakers.

Yes, it has an amp insert. I guess I didn't realize that I could use the mixer portion at the same time I used the other.

So it becomes:

                                                  --> L/R to Mixer Amp Insert --> Tops
       Pwr Mixer --> L/R to Crossover
                                                  --> Mono to Powered sub


To close the loop on an update, I have now fully tested the amp insert stuff, and sure enough -- if you run in L/R stereo mode on the PMH3000, but keep the Main output fader all the way down, you can send mono to a crossover. Then take the HF / LF out and feed it into the L/R channels respectively via the power amp inserts.

This allows me to run my two 12" tops from one channel (400W into 4 ohms) then either run the monitor from the other channel (200W into 8 ohms), or run 200W into a passive subwoofer (probably not enough, but better than nothing).

I can also run the Mono out to the right channel, if I need some back room fill. Then use a powered subwoofer. Or I could choose a passive subwoofer at 8ohms and bridge the PMH3000 amp into that for 800W, then use that with my active tops. That may be what I do, in fact.

In short, I have plenty of options now that I know my powered mixer is a flexible power amp and not married to a stereo or fixed mono/mon1 setup.

(I was thrown off by the PMH3000 being mislabeled on the back -- it had output B labeled as output A and vice-versa. That made all my first tests not work, and it wasn't until I thought to test the other output that it all made sense.)

Thanks to all for the help -- I am now comfortable moving to mono mode, and have finally also gained confidence on wiring speakers in parallel to reach 4 ohms and boost overall power output. I can end up pushing both tops via one channel in mono and get the same volume I got using both channels. That allows me to toss my little monitor amp for my usual gig setup and run the monitor from the powered mixer. Then I can use the rack slot for the compressor, which I had wanted to do for a while.