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Impedence Setting on Amp !

Discussion in 'AV Receivers & Amplifiers' started by Deeez Nuuutz, Oct 21, 2005.

  1. Deeez Nuuutz

    Deeez Nuuutz
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    Hi,

    I have a Yamaha RX-V4600 and M&K speakers. On my amp i can select between 2 settings for the impedence - 6 ohms & 8 ohms. I have also read the manual and these are the only 2 settings.
    The problem is (yep, you've guessed it) my M&K's are 4 ohms (3 x K17's & 2 x K4's).

    So what am i supposed to set my impedence to on the amp and will it harm my amp or speakers in the long run??

    Slightly worrying!

    Many thanks,
     
  2. Cable Monkey

    Cable Monkey
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    Set the amp to 6 ohms. This effectively increases current available and cuts voltage making the amp more able to drive the lower impedance. Also allow for plenty of ventilation because the amp will generate more heat.
     
  3. Deeez Nuuutz

    Deeez Nuuutz
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    Thanks alot!

    I'll do that then. A bit silly of Yamaha to only have the 2 settings, they must know that some speakers are 4 ohms so why do this!?

    I have the amp on the floor on the carpet at the moment with nothing on top of it.
     
  4. pragmatic

    pragmatic
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    Most amps only have the 6-8 setting, alot of speakers do get down to 4 and below and they can drive them, i suppose its a case of if its 8 or above pick 8 (if there easy to drive) otherwise pick 6.
     
  5. Deeez Nuuutz

    Deeez Nuuutz
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    Thanks for your help and information!

    ;)
     
  6. joffy1780

    joffy1780
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    I was going to ask a similar question.I have speakers which state nominal impedance of 4-8 ohms and have to choose 6 or 8 ohms on my amp,am I right in thinking I should set the amp to 6?
     
  7. pragmatic

    pragmatic
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    Its the closer match so logicaly the better choice.
     
  8. joffy1780

    joffy1780
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    Cheers.What actual difference will it make?
     
  9. pragmatic

    pragmatic
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    At 6 ohms i would get more current would be sent to the speakers than other would and in general more power is sent, there was an analogy for what the differnt ohmage means but i can't really remember it.
     
  10. joffy1780

    joffy1780
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    Thanks for your help Gazarber,might have a read on this. :thumbsup:
     
  11. chedmaster

    chedmaster
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    its the resistance the crossover/drivers present the amp. the lower the resistance the more current is used because its easier for the current to flow, and higher end amps are needed to cope with this extra current (better power supplys). On top end amps, as the resistance halves of the speakers (eg 8 ohms to 4 ohms), the power will double, but theres a limit as to how much current the power supply can provide.

    EDIT: in theory, the power output is inversley proportional to the impedance of the speakers, assuming the power supply can provide infinite current :D. You need to tell the amp the impedance so it can apply the necessary limits i think.

    thats using a combo of my A level physics and my hi fi knowledge, merged with a blurry line. someone like eviljohn2 would know better :)
     
  12. joffy1780

    joffy1780
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    Cheers,Chedmaster.Just reading an article with an analogy to water pipes,pressure etc..That may have been the one gazarber was thinking of.
     
  13. chedmaster

    chedmaster
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    thats how they teach at school these days :thumbsup:
     
  14. eviljohn2

    eviljohn2
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    You shouldn't confuse resistance with impedence ched, resistance is the simple part of the impedence but you also need to consider the complex reactance in this instance (saw your car earlier btw :thumbsup: ). If you're doing the maths that is.

    For maximum power transfer you need to match the input impedence of the speaker and the output impedence of the amplifier although this isn't relevant as I havn't come across a single cable manufacturer which impedence matches speaker cables. It's of little relevance for such low values anyway so I'm going off track...

    Briefly in laymans terms, the output voltage of your amplifier is what determines the volume of your speaker. A higher voltage equates to a higher volume and this is the case for all speakers.

    Speakers which are regarded as difficult loads do require more power but since the output voltage can't be dynamic (or else you'll hear rapid and uncontrollable volume changes which would be rubbish) we need to supply more current to make up this additional power. In general, you need twice as much current for each halving of impedence as has already been described so you are best setting your amplifier to 6ohms which will improve current output capability.

    Be aware that the number quoted by the manufacturer is only the nominal impedence (ie. the highest value it can take and where it spends most of it's time) but that impedence varies with frequency so if you're playing low frequencies through a speaker the speaker impedence will be lower - sometimes dropping to 2ohms or less for short periods of time. This is why big speakers that play low frequencies need much bigger amplifiers which can provide the current into them at low impedences without giving up.

    Also it's worth reminding people that high voltages aren't particularly difficult to reproduce. High currents require far more effort in design and components. :lesson:

    I hope I didn't bore too many people with what was hopefully a fairly non-techy explanation. :)
     
  15. chedmaster

    chedmaster
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    there you go :D here i come bath university (physics/maths joint) :)

    (edit: where did you see my car?!)
     
  16. Adrenochrome

    Adrenochrome
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    I Have a Yamaha DSP-AX750SE and have recently got some M & K MPS 1510 and M & K K-4s so sent an email to Yamaha for advice this wrt to running this combination here is the reply.

    Hi,

    Yes these speakers will work well with the amp. They are rated at 4 ohms - I would personally leave the amp set to 8 ohms and only drop the setting to
    4 if you experience problems (if the amp cuts out). as you will end up with better performance.
     
  17. mgh0001

    mgh0001
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    howdo,
    hope you can advise, i have the sony tan-9000es 5 channel power amp, which has a nominal imp. of 4ohms or 8ohms switchable or in bridgeable mode (btl) 8ohms or 16ohms. i have a pair of sony ss-x90ed which are rated at 4ohms per speaker. i have the amp on 4ohms nominal mode. is this mode ok or will it damage the amp or speakers, also would i be able to use any of the other modes?

    cheers, mike
     

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