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Ohm ratings

Discussion in 'Home Cinema Speakers' started by Samoz, Dec 21, 2004.

  1. Samoz

    Samoz
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    Hi,

    Can someone explain Ohm rating on Speakers and Amps? I recently bought Pioneer VSX-D712 rated at 8 Ohms and due to ignorance bought a pair of MS903 surrounds rated at 4 Ohms. Is lower the Ohm the harder to drive? Will I have impaired audio? Anything I can do to compensate it? I can't return the speakers as they were through a private sale not dealership.

    I haven't tried them connected yet as I am waiting for the speaker cables to come.

    Cheers
     
  2. ahin4114

    ahin4114
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    Samoz

    A speaker rated at 4 Ohms is harder to drive becuase it offers less resistance to the current passing through it. Therefore more power is required to drive it. But fear not, the rating on your amp is simply to show how much power your amp has when driving 8 Ohm speakers. Power is dependant on the resistance applied to it, so many manufacturers use 8 Ohm as a constant to ensure it's easy to compare power between different makes and models. I don't know how much power the Pioneer has, but do not assume it won't drive the speakers simply becuase of the rating.

    HTH
     
  3. Samoz

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    Ahin4114,

    Thanks for the insight. I can sleep better tonight. :thumbsup:

    Regards,
    Sam
     
  4. scrapbook

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    So would that mean you have less power being produced by the amp if more is being used to drive the 6 Ohms speakers?

    I notice that some Amp manufactures quote a 6 ohms figure, but this seems to be done to exagerate the actual power performance. Why is that? I would have assumed that the power output would be greater if the were driving say 12 Ohms speakers if they were easier to drive?
     
  5. ahin4114

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    Casting my mind back to A-Level physics:

    Power is calculated by current x voltage (P = IV)
    Ohm's law states that Voltage = Current x Resistance (V = IR)
    therefore Power = Current squared x Resistance (P = I²R)

    So if Resistance is reduced, then so is power. I think the important thing to consider when looking at an Amp is how much current it can provide as it is this that actually makes the speakers work. As you reduce resistance current needs to increase to provide the same power.
     
  6. Mylo

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    Please note the speaker rating is its Impedence not its resistance :lesson:
    just to be exact :D
     
  7. Nick_UK

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    Be careful ! Some amps can be damaged by connecting the wrong impedance speaker - you should refer to the manual. Most modern amps can cope with the mismatch, but a blown output stage can be expensive to repair, so it's a good idea to check first.
     
  8. ahin4114

    ahin4114
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    Mylo, you say 'Potato' but it's still a spud right :D

    And as Nick says, check the manual, usually if it's going to cause a problem there's a hard to miss warning somewhere. I would say though that if you haven't seen a warning (hence your question) you're probably going to be ok.
     
  9. Mylo

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    similar but not the same
     
  10. Kazman

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    I used to have the 903's, and had no problems driving them with my previous Marantz SR4300 and current SR7400 (both amps give a power rating stated at 8 ohm impedence), you shouldn't have any problems, but always best to check the manual.
     
  11. Samoz

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    Thanks all for the replies.

    I checked the manual but not much info there. Just indicates 100W/channel and has max power of 500W. The only thing with impedance mentioned is Input(Sensitivity/impedance) for sources CD,VCD/DVR,CD-R/TAPE/MD,DVD/LD,TV/SAT: 200mV/47kOhm.
     
  12. eviljohn2

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    If people really want to get technical with regard to resistance, impedence (and reactance) I hope you've all got a good understanding of complex numbers.

    Impedence is the whole "thing" and is what should generally be applied when considering hifi examples.
    It is comprised of a real "resistance" (like you learnt about at school) and a complex "reactance" which you probably didn't. The 3 are not interchangable :lesson: :suicide:

    Getting back to the power and amplifier issues, the equations that ahin derived are correct (although not the whole truth) (BTW, how did you do the index?). It follows from these that the ideal amplifier should double it's power output as impedence halves. Only very few high end amps can manage to even get close to this - generally the huge Krell monoblocs etc.

    I would expect the Pioneer to be able to manage adequately with your speakers but wouldn't recommend cranking the volume too high. Your upgrade path should certainly include demoing additional power amps in the future if you still want to get more out of your equipment. :)
     
  13. pjclark1

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    opps
     
  14. Mylo

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    Hi John, thanks for clearing that up mate :)
     
  15. eviljohn2

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    Not to worry, if enough people do it the rule of bad hifi magazine science will soon be crushed! :laugh:
     
  16. scrapbook

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    I have a Pioneer 812 and I was looking at some 6 ohms speakers the other day,
    the manual tells me to only use 8 ohms and above so this is defo going to be the case with the 712!

    In face come to think of it..i belive it is the same manul for the 712/812/912!!
     
  17. bob1

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    Pioneer don't recomend 4ohm speakers for their amps ,that doesn't mean it won't drive them, but they must say that for a reason.
     
  18. Samoz

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    Thanks for everyones kind input. I am now a little more at ease with this Ohm ratings business. :beer:

    I noticed some of you have Pioneer DVD players, any idea if the DV344 plays double layer discs? I know this machine is superseded sometime ago but 1 has come up as secondhand. Any recommendations for a new or SH DVD player of any brand to compliment my D712? I probably won,t upgrade it for a while. Hmm, perhaps I should start a new thread.
     
  19. bob1

    bob1
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    I had a pioneer 444 dvd player ,much better than the 565 i have now.
     
  20. Tejstar

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    The older Pioneer's were much more sturdier than recent ones. I've still got my Pioneer 636d which is nearly four years old and still works fine :)
     
  21. bob1

    bob1
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    I agree the 444 was rock solid and never faultered playing discs.
     
  22. Tejstar

    Tejstar
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    The newer players, like the 575, seem like they'd snap at any given moment :laugh:
     
  23. bob1

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    I wouldn't like to drop one,why do you think there cheap.I have never been in side the pioneer but i have one of the kids £40 dvd player and cheap isn't the word.
    I think what were saying if you can get a good old player grab it.
     
  24. Samoz

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    Just come across some SH Onkyo DV-S525, how much better is this compare to the Pioneer DV344. I see you mentioned 444, perhaps the model are named differently in Oz. I read the review for S525 and wasn't favoured due to the price. But if second hand how much more should I pay for the S525 compare to 344/444? Double perhaps?
     

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