Blog Forums DIY Speakers and Subwoofers QSC Powerlight 3.4 for two Sealed UM18-22

last updated by splinter 1 year ago
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9 replies
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    • #14757

      Hi Guys,

      Got a bit of a dilemma I’m struggling to resolve. I have two UM18’s on the way and am going to have them sealed in boxes just over 5 cuft, and placed in opposed corners of my room (6m x 3.6m). 

      I was planning to get a berry NX6000 as so many recommend, however I have an option of 2nd hand QSC Powerlight amps.

      Do you think it’d be better to get one 3.4 or two 1.8’s, costs being equal? Or would one 1.8 be enough to drive two sealed UM18’s? I’m wanting to touch the low teens in freq response, but probably have relatively low listing levels compared to many of the guys on AVS. Currently running a single PB1000 with the volume at 1 o’clock.

      Currently feeling that the 3.4 is the best choice just to have gobs of headroom even if it’s the more expensive choice. Hopefully a fan mod wouldn’t be too tricky as I expect it to be a bit noisy, been run as a PA amp for prob 20 years.

      I already have a Mini DSP 2×4 HD and UMIK1.

    • #14759

      @splinter I completely agree with you the one 3.4 is the way I would go.  That will give you about 1225w to each subwoofer, which should be plenty.

    • #14823

      Thanks for the input @123Toid, the 3.4 arrived today.

      I’m going to swap the fan out for a Noctua and also change the old traditional speaker terminals for speakon jacks.

      Have a question, the current speaker terminals are are attached to a little PCB and also grounded to the chassis. Do I need to be concerned about any stored charge zapping me while removing the PCB, and how should I connect the chassis ground to the speakon jacks? I have standard 4 pole (will wire the +1 and -1).



    • #14826

      I went ahead and disconnected that PCB and took it all off haha. So my only remaining question now, is what to do with the ground cable that connected to the chassis?

      Effectively I’ll be removing the ability to run it in bridged mode but that’s fine for my purposes. Would need a proper technician to perhaps add a switch and possibly third speakon for bridged mode only but I won’t bother with that.

    • #14840

      @splinter Honestly I do not know.  I would maybe ask @tvor-ceasar . He really knows a lot more about this then I do. 

    • #14845

      I’m still out at my son’s place for the holiday. I’ll have to take a look over the weekend, probably research the amp a bit before hazarding an opinion. Different topologies require different approaches.

    • #14850

      @tvor-ceasar Enjoy!  I hope you had an excellent holiday!  

    • #14853

      Got the two Speakon jacks for the outputs attached. I didn’t bother about grounding to the chassis (unless someone reckons I should!).

      Double triple and quadruple checked that the + & – were correct. Got a Noctua fan coming on Monday or Tuesday. No bridged output possible but that’s fine for my purposes.


    • #14902

      The power amp mods are all complete. I had to get a small buck converter to take the amp fan header voltage down from 24v to 12v to match the Noctua fan. Made a big improvement as the old fan was super loud.

      I ended putting the low noise adapter on the fan, spins a bit slower but still puts good amount of air through. I don’t think this amp will be driven to the extent that more cooling will be required.

    • #14903

      Pics, slightly dim but you can see where I blue tacked the convertor to the chassis bottom.


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