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Whats the point of lower ohmage?

Discussion in 'Home Cinema Speakers' started by Brad_Porter, Feb 23, 2003.

  1. Brad_Porter

    Brad_Porter
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    Yep - its me with my silly technical questions again. ;)

    What is the point of having 4 ohm speakers then it takes more current out of the amplifier? Why not just make all speakers 8Ohms or above?

    Probabley a simple answer to all this but - if you dont know the answer, you just dont know the answer!

    Cheers guys ....
     
  2. MJS

    MJS
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    Well, like you said it takes more current out of the amplifier. Power is related to current squared so the amp can deliver more power into a 4 ohm speaker than an 8 ohm one. That's the theory - in practice amps aren't ideal and the power supply in the amp will have its limits. I think that most amps nowadays are built with 4 ohm loads in mind (8 used to be the norm).

    Actually - this opens a huge can of worms because amp manufacturers use all kinds of tricks to give us the rated power of their amps. A high end manufacturer may quote power output into 8 ohms before clipping (distortion cause by power supply reaching its limits) that may seem ridiculously small compared to your average consumer amp. You could drive only one channel to give the power supply an easy time - you can quote power at up to 10% distortion (very clipped) or into 2 ohms etc...

    Has anybody actually figured out how a little wall adapter can power 200w computer speakers yet? I'm still working on that one.

    Mark.
     
  3. stranger

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    maybe they're 32ohm.
     
  4. mjn

    mjn
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    cos they quote PMPO...which means nothing
     
  5. Brad_Porter

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    Thanks for the reply - but I still dont get it. Why make speakers with 40hms impendence when an 8Ohm impendence will just put less strain on the amp? Why make a speaker that will ask most amps to do more?
     
  6. sounddog

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    Probably becuase at lower ohms, they can make a better speaker - I don't know this ... and it's not scientific or anything ... but it's the better higher end speakers that tend to be 4 ohms speakers. It's probably a compromise for manufacturers to make 8ohm but it makes them easier to drive.
     
  7. EvilMudge

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    Larger, more powerful electromagnets will normally have a lower intrinsic impedance than a small one.
     
  8. Brad_Porter

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    Thanks all......
     
  9. Dimmy

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    it's not called 'ohmage', it's called impedence.
     
  10. Reiner

    Reiner
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    The combination of x-over and drivers also influences the resulting impedance (2, 3-way design etc.).
     
  11. Bonesy

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    Can I just clarify my thinking ? -

    So, 4 ohm speakers have cones/magnetics that are easier to drive, ie. less resistance. And better quality speakers tend to have better quality components, lower impendance, , etc.


    so, if it is easier to drive, one might think that you need a less powerful amp to run...

    but in reality, it means that you need a more powerful amp, not because it is harder to drive, but because the speaker's lower resistance allows it to accept much more power, thereby running the risk that it draws more that the amp can deliver, and the amp runs out of steam?
     
  12. Reiner

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    So, 4 ohm speakers have cones/magnetics that are easier to drive, ie. less resistance. And better quality speakers tend to have better quality components, lower impendance, , etc.

    Nope, less resistance means it will draw more power and thus is harder to drive (from an amps point of view).

    so, if it is easier to drive, one might think that you need a less powerful amp to run...

    That statement as such is correct.

    but in reality, it means that you need a more powerful amp, not because it is harder to drive,
    but because the speaker's lower resistance allows it to accept much more power,


    As mentioned above it is harder to drive and thus it needs more power to function.

    thereby running the risk that it draws more that the amp can deliver, and the amp runs out of steam?

    Yes. That's why it's called hard to drive. The same applies to the sensitivity (measured in dB) of a speaker: the lower the more power required => the harder to drive.
     
  13. Bonesy

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    Cheers Reiner, cleared that up for me.;)
     
  14. mattheu

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    Its always interesting to note that a speaker is a reactive load, ie. impedance not resistance and varies with frequency, and although a speaker rated at a nominal impedance of say, 8 ohms, it could, over the frequency range, vary from 1 to 16 ohms and thus could still be diffcult to drive. ( it would be a pretty lousy design, all said)
     
  15. EvilMudge

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    What you mean like an electrostatic or ribbon/dynamic cone hybrid design?;)
     
  16. Reiner

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    Mattheu is spot on. I think the rating by the manufacturer is rather the DC resistance (which you can actually easy measure with the Ohm-meter) as to check the compability with the amplifier.
    A Dynaudio Contour 1.3MkII is labelled as a 4 Ohm speaker but the actual impedance varies from 3.5 - 14.4 Ohm (manufacturers claims).

    A speaker quoted under DIN should not drop more than 20% below the stated value though some do not comply and drop down even further, e.g. Infinity Kappas are known to go towards 1 Ohm - hence the nick name "amplifier killer". :D
     
  17. gjflong

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    On a slightly different tack - My fronts are 8 Ohms, Rears are 6 Ohms and my Centre speaker is 4 Ohms. Does this make them more difficult to balance?

    I am about to change the speakers for 6 Ohm speakers driven by an Arcam A85 (fronts) and Denon AVR 2802 (Rears, Sub Woofer and Centre) all linked through a tape loop!!

    With this new set up I'm having to boost the fronts far more than the others to achieve balance. Is the Ohms difference the reason for this?
     
  18. nathan_silly

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    No

    The reason it's different volume is- amps have different gain, and speakers have probably different sensitivity.

    nathan
     

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