How to power 4ohm speaker with 8ohm reciever?

Discussion in 'Archived Threads 2001-2004' started by Cole M, Jan 12, 2002.

  1. Cole M

    Cole M Auditioning

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    I just disovered this site about a week ago, and it has been very helpful. Reading the posts, it looks like everyone loves the SVS subs. I'm interested in getting one, but I need to know if it is possible to power the

    25-31CS with my reciever. My reciever is 100w x 6ch RMS, with 5 channels for the fronts, center, and surrounds, and one channel to power a passive sub. Since the SVS subs are 4ohms, how can I power it with my reciever which is rated at 8ohms/channel? Can a 4ohm sub be wired someway so it will carry a 8ohm load? I don't want to damage my reciever. Any help would be appreciated.
     
  2. Jim_C

    Jim_C Cinematographer

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    Is that 6th amp really designated to drive a sub? What receiver do you have?
     
  3. Cole M

    Cole M Auditioning

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    Yes, the 6th channel is designated to power a passive sub. The receiver has a built in crossover. I can cut the sub off from 200hz, down to 50hz. You can adjust the power to the sub through the receiver. The settings are off, 1 through 25, with 25 being full power. It is the .1 channel in the 5.1 surround sound.

    My receiver is a Panasonic SA-HT280. It has a sub pre-output too. Right now I am using the sub that came with the receiver to run off of the 6th channel, and a 200w powered sub running off of the pre-output. I figured a SVS sub would be a lot better than the sub that came with the receiver.
     
  4. ColinM

    ColinM Cinematographer

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    You CAN run the SV CS series with that 100 watts. Ive talked to Tom and he came up with figures verifying my belief that they are very efficient, and can reach good levels with 100 watts or less.

    I'll bet, however, that the amp is not really capable of 100 watts, it's just spec'd that way. Don't feel bad, many amps are over-rated these days.

    However, even with the 35 watts I got off of an old amp that I used for a couple of weeks, I never felt like I was missing anythingwith the 20-39. I just got some ultimate authority in the loud, deep authority dept when I moved to 165w.

    Good Luck

    - CM
     
  5. ColinM

    ColinM Cinematographer

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    Oh yeah, the 4-ohm thing...

    It'll be fine.

    Keep an eye on heat buildup, and don't try to reach the max as soon as you get it hooked up. Start slow.

    But you should get good results.

    If your manual says 'NO F*****G WAY' to 4 ohms, though, I'd really think twice. Then I'd do it anyway!!
     
  6. Cole M

    Cole M Auditioning

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    Thanks for the input.

    Your probably right about most receivers being overated. If I power the SVS sub which is 4ohms,with a 100w at 8ohms channel, there will probably actually be over 100w RMS or so due to half the impedence. I agree that even 100w would be enough power for the SVS. I would probably only have the sub up half way most of the time anyway. There is a fan on the back that kicks on when the heat levels build up, and it is a good indicator of when the receiver is producing to much heat.
     
  7. Jon_R

    Jon_R Stunt Coordinator

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    Cole,
    The problem you aren't understanding is that the receiver, though it says 100 watts, will likely not produce 100 watts RMS. Perhaps peak, but that could be with a great deal of distortion. A true 100 watts is quite a bit of power.
    As stated, many receivers quote higher wattages then are actually possible. Companies measure them at 10k hz on one channel of output and they get 100 watts. But when you do a full spectrum on all channels they output significantly less.
    That is just a way receivers can look more powerful. Also, with lower end receivers (I don't anything about yours) usually the top 3/4 of the volume is high distortion.
    HOWEVER, it should run the SVS temporarily just fine. With all that sub, you'd want more. And if you think you didn't want more, wait until you hear it, then you'll want more. [​IMG]
    Good luck,
    Jon
     
  8. Cole M

    Cole M Auditioning

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    I see your point. My thinking was that a 4ohm load would allow more power to flow than a 8ohm load. Even if the receiver was not putting out 100w at 8ohm, it might with only a 4ohm load. That was my thinking. By the way, what is a good THD rating for a receiver from say 20hz to 20Khz?
     
  9. ColinM

    ColinM Cinematographer

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    .07 or less, 20Hz - 20kHz, all channels driven at 1w into 8 Ohms indicates a good system.

    .7 at 1kHz, 1w into 6 Ohms indicates number tampering...

    Distortion is inaudible up until about 1%, or more.

    Don't quote me on that now, it's been a long time since I've read that article somewhere....

    - CM
     
  10. RichardH

    RichardH Supporting Actor

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    Colin has good points. You have to look at how the power spec was rated. 100w at 1kHz is a lot easier than 100w from 20-20k.

    Distortion is more audible in the speech frequencies and less so in bass frequencies.

    Good amps will double their power output when halving the impedance. Don't know if your amp will or not.

    I'd try it out, but it's probably not the best as a permanent solution. You could grab that $79 KLH receiver at Best Buy or find a ProLogic receiver that's laying around.
     

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