Sub driver for 200w @ 3 Ohms?

Discussion in 'Archived Threads 2001-2004' started by DaveVan, Jan 28, 2003.

  1. DaveVan

    DaveVan Extra

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    I need to replace the original subwoofer that came with the RCA RT2500 theatre in a box system. It was a small box, less than a cubic foot, with dual 5" drivers. My guess is the drivers were each 6 Ohm wired in parallel.
    The subwoofer amp built into the receiver is rated for 200w into 3 Ohms.
    I would prefer a single 12" or even 10", but it seems there are none rated at 3 Ohms. I tried my bookshelf speaker rated at 6Ohms, but I really had to crank the volume to get anything out of it.
    Would it be reasonable to hook a single 4Ohm speaker to the 3Ohm output? Would there be a noticable decrease in output?
     
  2. Dustin B

    Dustin B Producer

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    There is no way the RCA receiver could handle a 3ohm load. Those drivers must have been in Series or have a higher impedance.

    Second, that RCA receiver won't have anywhere near 700W total like it advertises. You'd be lucky if it put out an actual 25Wx6 at 8ohms.

    Lastly what matters is the drivers impedance and if the amp can push it. If the amp can driver a 6ohm speaker, it will have no problem with speakers of higher ohm ratings. The problem is when you go to lower ohm rated speakers. These can ask for too much power and cause the amp to over heat and shutdown or wreck itself.
     
  3. DaveVan

    DaveVan Extra

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    I realize the power ratings on low end models like this are overly optimistic, but I dont have the original subwoofer to look at for impedance values.

    The specs say the sub output is 200w at 3 Ohms, so based on that a 6 Ohm driver at 100w should be ok. That is the same as my bookshelf speakers, but the volume was only about half of what it should be.

    What would be a good driver then? Im guessing a mid-priced 12" 4Ohm would be ok.
     
  4. Dustin B

    Dustin B Producer

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    I think that is ratings trickery. I really don't see that thing being able to drive a 3ohm load. They just said that so they could say it was 200W.

    http://www.partsexpress.com/pe/showd..._ID=7771&DID=7

    Won't be anything spectacular, but should work and will definately be better than the sub that came with it, provided you build an appropriate enclosure for it.
     
  5. BrianWoerndle

    BrianWoerndle Supporting Actor

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    Can I ask why you don't just buy a powered sub like the Sony WA-M40? I doubt that a little RCA receiver will give any speaker the juice it deserves. I am assuming that it was a cheap HTIB, so it probably doens't have a sub pre-out, but you could still use a powered sub wired from the front speakers. That is if the speakers use bare wire, and the receiver will let you say no sub and route bass to the fronts. Boy, the more I type the more things I think of that make the situation worse. OK, so you may just need a new driver that the RCA can push.

    Look at car subs. Most of them run a 2 ohms. If the RCA is really pushing 3 ohms, a car sub would match the closest. But that really scares me. I don't think the RCA can really run at that load without frying. I think RCA is being really deceiving with their numbers. All speakers have a 3 ohm point, it is just not a realistic one. i.e. My Denon 3803 is rated at 110w/ch @ 8 ohms, and 150w/ch @ 6 ohms, 7% THD. So I could make my Denon look really good by putting 250w/ch or so @ 3 ohms, but it would be at an insane THD. The RCA is probably pushing less than 100w @ 8 ohms normal load. So you need to find a driver with the highest sensitivity that you can. That is what will determine the volume. Not ohms.
     
  6. Tim Morton

    Tim Morton Stunt Coordinator

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    I have no way of knowing what the capabilities of the RCA amp in question are, but the way to get a driver with a 3ohm load is to get a DVC sub rated at 6ohm per VC..then wire THAT driver in parallel. madisound sells them...look in the catalog at vifa drivers.
     

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