Is 200w at 4ohm the same as 400w at 2ohm?

Discussion in 'Mobile Phones / Entertainment' started by Matt Odegard, Nov 20, 2003.

  1. Matt Odegard

    Matt Odegard Stunt Coordinator

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    Someone told me this today, and I don't believe it. Although at the time I could not explain why he was wrong. I just never heard of such a thing in the time i've been in car audio.

    Also, why would manufacturer's give statistics of their amp power rating at 4ohm, 2ohm and 1ohm? If there is no difference in power besides THD.

    Can anyone tell me why he is wrong? Or why I am?

    I know amps give out more power at 2ohm because there is less resistance than at 4ohms. But that doesn't meen its the same 200w being pushed to the subs. Correct?
     
  2. VinhT

    VinhT Second Unit

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  3. brentl

    brentl Cinematographer

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    "On cheaper amps, the power increase between four and two ohms will be marginal, and the amp itself will not even be one-ohm stable."

    I wouldn't that's true. Amps with well regulated power supplies aren't always the "cheap" amps.

    Not only Cheap amps are unable to run into 1Ohm!

    Brent
     
  4. Matt Odegard

    Matt Odegard Stunt Coordinator

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  5. Sean^M

    Sean^M Stunt Coordinator

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    simple answer:
    Ohm's Law.

    disregarding the loss to inefficiency, as you halve the impedance, or load on the amp, the power output will double within the range the amp is able to operate.
    If the amp isn't a "high current amplifier" then that range is usually 2 to 16 Ohms.

    high current amps can go as low as 0.5 Ohms stereo and even .67 Ohms bridged.

    Now, some amps, like JL Audio slash series amps use a regulated output that keeps the same power output regardless of load. This way using a 2 Ohm load gives the same power out as a 4 Ohm load.

    if an amp is:
    300 watts x 2 @ 4 Ohms
    then it will be:
    600 watts x 2 @ 2 Ohms and
    1200 watts x 2 @ 1 Ohm
    bridged, the amp will produce:
    1200 watts x 1 @ 4 Ohms.

    this is just an example, and again, not counting a slight decrease in power output as the impedance drops due to loss in heat or efficiency.
    Also note this applies to class A, AB, B, and D solid state amps.
    this isn't the case for tube amplifiers which gain very little in output by lowering the load.

    more info can be found here:
    http://www.eatel.net/~amptech/elecdisc/
     

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