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8ohm car audio subs? What amps, power rating?

Discussion in 'Audio' started by jjlaughner, Dec 23, 2002.

  1. jjlaughner

    jjlaughner 3/4 ton status

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    OK, I picked up some 12" MTX black golds off ebay. I get them and they are 8 ohm. I know MTX made the 4 and 8 ohms for car audio but I'm not sure what or how I need to wire up 8ohm subs. Do I just put ALOT of 4ohm power to them or is there a x-over configuration or special amps?

    FYI, I have audio wise wired in right now:
    New Alpine cd/MP3 player in dash
    memphis power reference 3.5" dash speakers on caps (powered from deck-front)
    MTX 3000 components 6.5"/1"tweeters (x-overs build in, powered from deck-rear)
    2- 10" (4ohm) MTX black golds -rear preamp outs from receiver on a Memphis 16st-300 amp (150x2 rms - 4ohm)

    I would like to stick with the memphis amps, style but I also have to wire in (future):
    2- 6.5" 8ohm midbass subs (to be on deck's front preamp out)
    2- 8" 8ohm subs (to also be on decks rear preamp out with 10's)
    2-12" 8 ohm subs (to be on subwoofer preamp out)
    (any set or combomantion of may be used, I have an idea for the 12's and 10's in an angled box and the 8's in the side panels and the 6.5's in the kick panels up front with a directional tweeter (also MTX BG))

    Any ideas? /forums/images/graemlins/confused.gif
     
  2. Prembird

    Prembird 1/2 ton status

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    ok if i was you.. this is what i would do...

    3.5 off of front preouts w/amp..

    6.5/tweeter off of front preout w/ amp

    6.5 off of rear out w/amp on side panels behind driver and pass. doors..

    12's and 10's off of sub outputs w/amps

    So basically what we have is pretty simple... the 3.5/6.5/tweeter off a 4 channel amp..

    The 6.5 (for rear fill only) off the rear outputs of the radio..

    The 10's/12's off two seperate amps in the back...

    from what you are stating that you already have... I would recommend getting a good 4 channel amp and another amp for the 12's.. Total of 3 amps... Also since you putting all of this in you better make sure you have the right power blocks and i would recommend getting a 1 farad cap at the least...

    Hope this helps..

    As for the 12's... since they are both 8 ohm subs.. wire them in parrellel to get a 4 ohm rating then bridge an amp into them.. .
     
  3. jjlaughner

    jjlaughner 3/4 ton status

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    sounds good, I like the Memphis belle amps I have been watching them on ebay.
    -As for the cap would you wire it in front of the power block or in front of the 12" sub amp?
    -Also, if you are wiring the 12" subs in parallel to a 4ohm amp that amp would need to be MONO right?
    Thanks again! Jeremiah
     
  4. Prembird

    Prembird 1/2 ton status

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    For placement of the cap... I would think you would want to place it before the sub amp since that is where your major draw will be coming from...

    On the amp for the 12's.. you can use a mono block amp or you can use a stereo amp bridged.. basically that is taking both sides of the amp and making one output from it.. Now when you bridge an amp into a 4 ohm load the amp will see it as a 2 ohm load since it is splitting it between both sides of the amp... Now the mono block is just a one channel amp to begin with so it will see the subs as a 4 ohm load...

    hope that helps..
     
  5. jjlaughner

    jjlaughner 3/4 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />
    hope that helps..

    [/ QUOTE ]
    Thanks! Thats what I needed to know. Now I just have to find a resonably priced memphis amp around 1000/1500watts (the 1000/1500 rating is at 2ohm so 4ohm would be half that /forums/images/graemlins/rolleyes.gif )
    Thanks again, J
     
  6. purple76pearl

    purple76pearl 1/2 ton status

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    that memphis amp is 4 ohm stable brigged, which is a lil over 350 watts, just wire the subs up and brideg them onthe amp, rem 8 and 8 make 4, but wire togeather 8 and 8 make 16? 4 is good and thats a good amp, memphis is my best seller run wiht it
     
  7. jjlaughner

    jjlaughner 3/4 ton status

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    Are the st16-400's 4ohm brigeable? Whats would that push at 4 ohm? I need a second amp anyway, the 300 is pushing my two 10's.
    OK, I have looked through the manuals, endless web searches and I still haven't figured out but if you bridge the amp doesn't it default to 2ohm?
    Do you have a wire diagram of two 8ohm speakers wired to a 4ohm bridged amp? (like what I'm wanting to do) I guess a diagram is what I really need, I'm not seeing it my head. /forums/images/graemlins/smirk.gif
     
  8. purple76pearl

    purple76pearl 1/2 ton status

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    ok i dont have a pic of it but let me try and walk you through it, if you have a + and - on each sub wire the + with each other and the - with other on the amp it shoudl give you +-+- on the speaker input the far right and the far left shoudl be brigged wire it up that way its 4 ohm brigged, hope that helps ya
     
  9. jjlaughner

    jjlaughner 3/4 ton status

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    ...P--------------P-------------P (bridged)
    Speaker..... Speaker..... Amp.... Straight through like this?
    ...N--------------N-------------N (bridged)
     
  10. purple76pearl

    purple76pearl 1/2 ton status

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    yep /forums/images/graemlins/k5.gif
     
  11. BozoWise

    BozoWise 1/2 ton status

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    That is parallel wiring. Want a better amp then the memphis? Look at the Crossfire. I sell them new if you want one or look on ebay for a used one. They are much better amps. Check out the world record holders. Never seen memphis in there.... /forums/images/graemlins/eek.gif
     

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