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XLS1500 with two JBL PRX 415M cabs


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#1 purpletornado

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Posted 22 May 2012 - 12:20 PM

I own an XLS 1500 that I would like to use to power two JBL PRX 415M cabinets, which are 8 ohms and are rated 300W continuous, 600 W progam and 1200 W peak.  Can I adequately power both cabs using one channel of the XLS 1500, which I believe will effectively deliver 525 W into each cab given a 4 ohm load?  If so, how do I connect the cabinets to the power amp and to each other to achieve this result?  If not, what is a better recommendation for a power amp to use with these speakers?

#2 dakos

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Posted 22 May 2012 - 02:40 PM

View Postpurpletornado, on 22 May 2012 - 12:20 PM, said:

I own an XLS 1500 that I would like to use to power two JBL PRX 415M cabinets, which are 8 ohms and are rated 300W continuous, 600 W progam and 1200 W peak.  Can I adequately power both cabs using one channel of the XLS 1500, which I believe will effectively deliver 525 W into each cab given a 4 ohm load?  If so, how do I connect the cabinets to the power amp and to each other to achieve this result?  If not, what is a better recommendation for a power amp to use with these speakers?
Do you need the other channel for something else?
The difference in wattage wouldn't be audible so in that aspect you're fine.
I haven't seen these speakers first hand but there should be two speakon plugs on the back of the speakers so you just daisy chain them (connect them in parallel from one speaker to the next) using speakon speaker cables such as these:
http://www.ebay.com/...101705#vi-desc.
What kind of music do you run through them? if it's stereo then you need to do something so you don't loose data.

#3 purpletornado

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Posted 22 May 2012 - 03:24 PM

Thanks for the reply.  I plan to use the system as a PA for band practice, so it will not need to be in stereo.  I realized after my original post that when two speakers are connected in parallel to the same channel, that the watts are halved, thus each speaker will only receive approximately 263 W, well below the program rating of 600 W.  Perhaps it would be better to run the cabs in parallel in bridge-mono mode, in which case I think each speaker would receive 775 W, if I calculated this correctly (per the XLS 1500 spec sheet, it delivers 1550W at 4 ohms when in bridge-mono mode, so 1550W/2 speakers = 775W per speaker).

#4 dakos

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Posted 22 May 2012 - 09:55 PM

View Postpurpletornado, on 22 May 2012 - 03:24 PM, said:

Thanks for the reply.  I plan to use the system as a PA for band practice, so it will not need to be in stereo.  I realized after my original post that when two speakers are connected in parallel to the same channel, that the watts are halved, thus each speaker will only receive approximately 263 W, well below the program rating of 600 W.  Perhaps it would be better to run the cabs in parallel in bridge-mono mode, in which case I think each speaker would receive 775 W, if I calculated this correctly (per the XLS 1500 spec sheet, it delivers 1550W at 4 ohms when in bridge-mono mode, so 1550W/2 speakers = 775W per speaker).
Your wattage calculations are correct. When you used the amp at 8 ohms per channel, you were getting 300W per cab so you can't hear a 37W difference.
This mode of operation, bridge mono into 4 ohm load, is not recommended, the amp will probably go into thermal protection sooner then you'd like. But, since you already have the gear, you should give it a try and see how it handles the task.

#5 Deromax

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Posted 23 May 2012 - 03:39 PM

In the context of a practice room, it may works OK bridged at 4 ohms.  The absolute reliability is less of an issue.  However, you may find that operation at stereo 8 ohms will produce enough volume.