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Make a passive sub "active"?

Discussion in 'Live Sound [BG]' started by lowfreq33, Jul 20, 2012.

  1. lowfreq33


    Jan 27, 2010
    Endorsing Artist: Genz Benz Amplification
    I've got a Peavey passive 18" sub. My mains and monitors are all powered. It occurred to me it might be more convenient to mount a power amp in the sub itself rather than carrying a separate rack with a single amp in it. One less thing to pack, etc. I'm pretty knowledgable with audio, but not so much with speaker design.

    My question is, if I cut a two rack spaced size hole in the back and mounted a power amp, say a Crown XLS 1000, taking care to properly seal all the edges, would the resulting loss of internal volume make a significant impact on performance? Would the cooling vent on the amp make sealing ineffective?

    This is probably a stupid question, I'm sure it's a bad idea, but I was curious what someone who knows more about speaker design thought.
  2. Hi.

    Unless You're going to go all the way and seal the space for the amp, IMHO it's a bad idea.

    Much better, and way more used way is to install a plate amp.

    Those are available in various configurations, usually with at least some cross over(s) and sometimes DSP.

  3. DuraMorte


    Mar 3, 2011
  4. uhdinator


    Apr 20, 2010
    Displacing the airspace in the cab would raise its freq response. Bad idea.
  5. modulusman

    modulusman Banned

    Jan 18, 2004
    Sell the Peavey before you ruin its resale value and buy a proper powered sub that matches your tops.
  6. lowfreq33


    Jan 27, 2010
    Endorsing Artist: Genz Benz Amplification
    Like I said, I'm sure it's a terrible idea, not planning on actually doing it. Just curious about the idea.
  7. Hi.

    It's a rare thing to see a mention of a Peavey product and "ruining the resale value" in the same sentence, but to each his/her own ;).

    Nothing wrong about the idea, only the choice of the amp isn't the most optimal one. IME/IMHO anyway.

    I'm planning the same exact thing with a 115 HK sub and a "spare" generic plate amp.

  8. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    Carry the rack or buy a decenet powered sub... The idea is ... Well smart isn't what springs to mind...
  9. Dantreige


    Oct 22, 2009
    I'm going to side with everyone else, not a good idea, IMHO. (I'll just be nicer about it. ;) )

    A plate amp would be best if you wanted to do this. Would the cost and hassle be worth the packspace saving you'd get over carrying the crown? Only you could decide that.

    I'd sell the peavey and the crown to fund an active sub that would match your other speakers.

    Good luck!
  10. horrible idea.

    the amp has airflow needs for cooling. So mounting the amp inside the speaker first of all changes the internal volume, and second, the venting the amp needs changes the port area.

    If you seal up the amp, you still have the internal volume changes, and the amp will overheat.

    No way to make it work.


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