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4ohm amp to 8ohm sub?

Discussion in 'Audio & Video' started by El Hombre Lobo, Nov 29, 2010.

  1. Nov 29, 2010 at 9:51 AM
    #1
    El Hombre Lobo

    El Hombre Lobo [OP] Member

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    I have a PDX5 putting out 300W @ 4ohms. I can get a deal on a JL 10W3v3-8 (8ohm) sub. Will putting an 8ohm sub on a 4 ohm amp reduce it's load to 150W RMS? Will I notice considerable sound loss? Would it not be possible to boost the gain on the amp itself and get maybe 200-250W?

    Thanks for the help!
     
  2. Nov 29, 2010 at 10:17 AM
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    buck

    buck the-eh-team.com

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    You won't get much out of that single 8 ohm sub on a 4 ohm amp. If you get a pair of them, you can properly wire to 4 ohm.
     
  3. Nov 29, 2010 at 10:24 AM
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    A7XTaco

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    Correct, at 8 ohms the amount of power being delivered to the sub will be half, so 150W.

    The 4 ohm rating is just the lowest impedance the amp is capable of handling. If you took that same amp and put it on 2 ohms worth of speakers, it would put out 600W. The problem is the power transistors wouldn't be able to dissipate the heat and would burn up... probably quickly.

    As to if 150W will play well with that sub, I have no idea... I'm sure someone will know.
     
  4. Nov 29, 2010 at 10:31 AM
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    A7XTaco

    A7XTaco Member

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    If you take two 8 ohm speakers and put them in parallel to drop the ohms to 4, you now have a voltage divider. True the amp will be putting out 300 watts, but each speaker will still only be receiving 150W.

    So if 150 watts is not enough to drive the sub, you will now have two under-driven subs.
     
  5. Nov 29, 2010 at 4:02 PM
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    rb11701

    rb11701 Oh yeah!

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    Is the sub a single voice coil or dual? If you bridge your amp you are putting a 4 ohm load on it, which is fine.
     
  6. Nov 29, 2010 at 6:46 PM
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    El Hombre Lobo

    El Hombre Lobo [OP] Member

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    Thanks for the replies.

    I can't tell if the sub is a single voice coil or dual. Perhaps someone can correct me?

    In any case, could I not boost the gain on the amp to get more then 150W?

    For this JL sub in particular the company says 300W is optimal while 150W is the bare minimum. If I could increase the amp gain to the 200-250W area I would be happy. Is this possible or is the amp limited to a ceiling of 150W when connected to an 8ohm sub?
     
  7. Nov 29, 2010 at 7:01 PM
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    rb11701

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    If you have two sets of speaker posts it is a dual. Single set, single coil. As far as the gain, it isn't the amount of watts you are turning up but rather the voltage of the RCA's. Think of a faucet. You only have so much pressure in your lines. You cna open the faucet up alittle and get a little stream, controlled. Open it up too much and it gets sloppy.

    You are not going to increase the amps. It is what it is.
     
  8. Nov 29, 2010 at 7:01 PM
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    A7XTaco

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    No probably not. If there was a way to up the power, it would start to distort. The problem with distortion is the peaks of the signal start to flat top(clip). The problem with this is the clips are a steady DC voltage. The voice coil dissipates heat because the signal is constantly varying. When its starts to clip it average power being delivered to the voice coil goes way up and can burn it up.

    The moral of the story is you can actually burn up a speaker by over driving it with under powered amp quicker than you can with a over powered amp. With a over powered amp your just more likely to physically damage the speaker... given it has good air circulation.
     
  9. Nov 30, 2010 at 5:36 AM
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    buck

    buck the-eh-team.com

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    If the sub was a dual voice coil, it would reflect that in JL's model number. Your model most likely isn't a dual 4 ohm voice coil, but rather a single 8 ohm.

    Your setup will make some sound, but no where near what it should. Your amp and speaker do not match up. It's also odd to have a single 8 ohm speaker setup.

    You should keep your eye out for a second identical sub, or get a single 4 ohm sub.
     
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