Expanding a PA system to using four LF enclosures

[Adam_Dawson]

Hi, I wonder if anyone can offer me any advice.

 

I currently own two passive Logic Systems X12 Full range speakers, which I use with two X15 passive bass cabinets, with internal passive crossovers. This is powered by a Yamaha power amp which delivers 1500 watts per channel into 4 Ohms.

 

I have recently acquired two more X15s and would now like to integrate these into the current setup, but I'm unsure how I should go about this. Should I now invest in an active crossover and purchase another power amp, which would obviously involve running out lots of speakons, or could I still keep to running just one speakon to each stack?

 

The X12s are 8Ohms and 400 watts and the X15s are 4 Ohms and 600 watts.

 

I'd really appreciate some advice on this, as I want to expand the PA to deal with the larger venues that we're now beginning to play to.

 

Many thanks,

 

Adam

[Shez]

I've got a similar Logic Systems rig. Currently, your cabs (assuming the crossovers aren't much cleverer than mine) are presenting an impedance of 2.6 ohms to your amp. If you connect another sub in parallel, you'll be presenting 1.6 ohms which your amp really won't like.

 

An active crossover and another amp would be your best bet. It'll need to be beefy though - at least 1800W in to four ohms. My system sounds better powered this way than with the passive crossover; you get much more control too. I usually only need one sub though; the last time I tried with two (600 seater hall) I had to turn them down so much to get a balanced sound it wasn't really worth having them both there!

[6th Order]

Just to check, I think an X15 is the 15" version of the X12 and the bass enclosure is called the X150.

 

If you have the budget, Bi-amping by adding another amp and a system controller will give you the best results.

 

It's worth checking if you can use the B6th order EQ to get some more bottom end out of the cabs. Try emailing the factory. You can then look to buy one of the X series controllers, or an XTA or BSS, which I believe they support and can send you the right settings for (though any good system controller should be able of doing the job.)

 

Also, if you do end up bi-amping it, I'd suggest a further tip of a (simple) rewire:

 

Get some 4 core speaker cables and run mid/high on 2 cores and bass on the other two.

 

All you need to do is make/buy a simple output panel to combine the two power amp outputs in to one 4 pole speakon. You can then either use a 1+- to 2+- converter on the subs output panel to feed the mid highs or rewire the output panel. You would need to check that the extra poles on the speakon panel are connected in the first instance.

 

On your extra subs, make sure all of the speakon poles are wired in parallel. With all of that done, your cabling would be

 

power amp panel out --> 4 core cable --> sub 1 --> 4 core link cable -->sub 2 --> cable converter --> X12

 

By using the cable converter, you could leave the internal crossover in place in the first subs, so that you could still use them passively if you ever needed to.

 

Of course, you should only try this if you have the required ability and understanding to do it safely, but it does make things quicker to setup.

 

HTH

[Adam_Dawson]

Thanks for your help. You're right, they are X150s.

 

I currently use Logics XB6 controller to add 6th Order, but I'm unsure exactly what I'd do if I get a second amp and an active crossover.

 

Could someone tell me exactly what wires to put where?

 

Would one amp power the first subs and the second power the sub and top run using the passive xover as I do now?

[Shez]

Would one amp power the first subs and the second power the sub and top run using the passive xover as I do now?

 

I'd be inclined to run the tops from one amp and the subs from a separate one. It's liable to be a bit messy otherwise in terms of what's coming out of what speaker.

 

According to the spec sheet for the XB6, it should be inserted between the low output of your active crossover and the sub amp. (It also mentions that you should never connect it with full range cabs; not sure whether they mean on their own or paralleled with subs as you're doing at the moment...)

 

Signal chain is thus:

mixer out -> crossover in

crossover hi out -> hi amps -> top cabs

crossover lo out -> XB6 -> sub amp -> subs

[jamesperrett]

I've got a similar Logic Systems rig. Currently, your cabs (assuming the crossovers aren't much cleverer than mine) are presenting an impedance of 2.6 ohms to your amp. If you connect another sub in parallel, you'll be presenting 1.6 ohms which your amp really won't like.

 

Are you saying that there is no high pass filter on the output to the tops - or no low pass filter on the output to the subs?

 

Cheers

 

James.

[Shez]

Are you saying that there is no high pass filter on the output to the tops - or no low pass filter on the output to the subs?

 

On my cabs (CM12 and LS115) there's no filtering at all going on inside the sub (at least as far as I'm aware; it's been a while since I had a look inside...) and the crossover in the top is simply a cross between its LF & HF drivers. The cabs are designed to be able to be run in parallel from the one amp. The two connections on the sub are certainly just paralleled.

 

The Logic website doesn't seem to have any info on the X12 / X15; I wish they'd put on an archive section for all us owners of older cabs...

[Adam_Dawson]

Would one amp power the first subs and the second power the sub and top run using the passive xover as I do now?

 

I'd be inclined to run the tops from one amp and the subs from a separate one. It's liable to be a bit messy otherwise in terms of what's coming out of what speaker.

 

According to the spec sheet for the XB6, it should be inserted between the low output of your active crossover and the sub amp. (It also mentions that you should never connect it with full range cabs; not sure whether they mean on their own or paralleled with subs as you're doing at the moment...)

 

Signal chain is thus:

mixer out -> crossover in

crossover hi out -> hi amps -> top cabs

crossover lo out -> XB6 -> sub amp -> subs

 

Thanks Shez, but could I run four subs (two per channel) from one power amp? The subs are rated at 4Ohms each, so surely running them together would present the amp with a very low impedance?

[Shez]

Thanks Shez, but could I run four subs (two per channel) from one power amp? The subs are rated at 4Ohms each, so surely running them together would present the amp with a very low impedance?

Two ohms to be precise. As long as you use an amp that's happy driving in to two ohms, you'll be fine. The ideal would be to use two amps so they each have an easier load of four ohms but that obviously costs more...

[6th Order]

Agreed. One amp running mid/highs and one running one or two pairs of subs. Beware of the two ohm trap andmake sure that your new amp can handle the load.

 

On the XB6: you shouldn't put the XB6 eq in to a mid/high as it's basically low boosting and will probably damage the mid driver. I would recommend using just one controller which can cross over and apply the required eq rather than a crossover and an XB6.

 

The CM and LS range do have different crossovers depending of which version you have and how old they are. The X series helps define the MI market and was originally designed for Academy of Sound as a plug and go range, whilst delivering good quality sound (plus Chris Scott had had enough of making carpet covered boxes!)

 

The resulting boxes are really quite different.

[Adam_Dawson]

Agreed. One amp running mid/highs and one running one or two pairs of subs. Beware of the two ohm trap andmake sure that your new amp can handle the load. On the XB6: you shouldn't put the XB6 eq in to a mid/high as it's basically low boosting and will probably damage the mid driver. I would recommend using just one controller which can cross over and apply the required eq rather than a crossover and an XB6. The CM and LS range do have different crossovers depending of which version you have and how old they are. The X series helps define the MI market and was originally designed for Academy of Sound as a plug and go range, whilst delivering good quality sound (plus Chris Scott had had enough of making carpet covered boxes!) The resulting boxes are really quite different.

Yes mine are the Academy of Sound ones, not carpet covered.Can anyone recommend a good crossover that adds 6th order EQ?Just to clarify then...I take my stereo outs, into the XB6, into the crossover. LOW LEFT and LOW RIGHT into POWER AMP 1 (capable of delivering into 2Ohms) and HIGH LEFT and HIGH RIGHT into POWER AMP 2.If I were to buy an additional Power amp, to power each pair of subs, how would the wiring differ? Would I need to split the Low frequency signal into two paths?Many thanks for continual help!

The resulting boxes are really quite different.

Yes mine are the ones from Academy of Sound bought about three years ago - not carpet covered.Can you recommend a good crossover which adds 6th order EQ?So just to clarify this, I would take my stereo outs into the XB6, then into the crossover and take the low Left and Low right into Power Amp 1 (which is capable of delivering into 2 Ohms) and the highs into Power amp 2.If I were to purchase two more power amps, one for each sub - where would my Low left and low right output from the crossover go? Would I need to split the signal into two amps?Many thanks for your continuing help!

 

 

Moderation: Two slightly different edits of the same material - I wasn't sure which of the duplicate elements to delete? Could you sort it please, Adam

[MarkPAman]

If you want to run two amps for the 4 subs, then you have a few choices:

1. 
   Use the links out of one amp to the inputs of the other (or a splitter lead), with each amp running one lef & one right speaker.
   If the amps are the same, and can be set up to mono (not bridged) mode use one for low left & the other for low right (again a splitter lead could do this if there's no mono mode).
   

[Shez]

Just to clarify then...I take my stereo outs, into the XB6, into the crossover. LOW LEFT and LOW RIGHT into POWER AMP 1

 

Nope, as stated above, the XB6 needs to be after the crossover, not before it.