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Ohms

Discussion in 'Home Cinema Speakers' started by scrapbook, Sep 16, 2002.

  1. scrapbook

    scrapbook
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    Who can tell me the relevance of 'Ohms'!?

    The reason I ask is that my amp currently runs some speakers at 8ohms, however the replacements I quite fancy are 6ohms. Will they work and does a reduction in 'ohms' mean a reduction is sound quality?

    Thanks in anticipation!
     
  2. bob007

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    Your amp won't have a problem running speakers rated at 6ohms, I think most amps these days can run speakers rated at between 4/16ohms with no problem, a reduction in ohms does not mean a reduction in sound quality.

    Go ahead and purchase them. :D
     
  3. buns

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    Ohms are a measure of impedence. It is basically a complex resistance. If the impedence is very low, the speakers are very hard to drive, if the impedence is high, they are easy to drive. 6 to 8 ohms is fairly average, so you shouldnt have any difficulties

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  4. lynx

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    Resistance is the measure of a device's opposition to the flow of electrical current. Its unit of measure is the ohm. If a device with one ohm of resistance is connected across a one volt power supply, the flow of current through the device will be limited to one amp. If the resistance is doubled, and the power supply voltage remains at one volt, the current flow will be one half amp. As you can see, more "resistance" will reduce the current flow in the circuit (if voltage remains constant).
     
  5. Ian J

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    It sure looked like English but I didn't understand a word :D

    I'll read it again in the morning to see if it's any clearer.
     
  6. Phil Hinton

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    What!? Why not draw us a diagram, cos you lost me.....:rolleyes:
     
  7. Duncan Craig

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    Your 6 ohm speakers will a little be louder than your 8 ohm speakers.

    The sound quality will be the same, but louder at the equivalent amp settings.

    Most amps are rated to run fully at 4 ohms (check your amp), but don't operate any lower than this.

    You can acheive 4 ohms by wiring two sets of 8 ohm speakers in parallel, getting roughly double the volume.

    Just don't annoy the neighbours!!
     
  8. buns

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    I believe i have had this discussion before! No amp, in my experience, has ever simply doubled the volume at a given setting because i used speakers of half the impedence.

    The way i read a couple of the posts made me think that the impression was that you could simply use lower and lower impedence for more volume......well thats not right!

    If you look at amp specs, you will notice power outputs are measured into specific impedences. Good amps will double the power output as you halve the impedence repeatedly. So using lower impedence effectively means the amp has more power, but conversely, the speakers are harder to drive and require more power to do it.......thus, is the net effect not zero!?

    If you want volume, you need to look at sensitivities, not impedence.

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  9. Reiner

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    Your 6 ohm speakers will a little be louder than your 8 ohm speakers.
    The sound quality will be the same, but louder at the equivalent amp settings.


    Absolutely not as the sensitivity (measured in dB) of the speaker also affects the volume level.

    In general a lower impedance means a higher load to the amp, i.e. while a 8 Ohm speaker would "consume" e.g. 50 Watt, an otherwise identical 4 Ohm speaker would draw 100 Watt.
    (Assume a constant sine wave at a certain frequency for this example.)

    Actually true 8 Ohm speakers are hard to come by these days.

    Most amps are rated to run fully at 4 ohms (check your amp), but don't operate any lower than this.

    Most amps which can handle 4 Ohm speakers must be able to handle less than that as the impedance is not a constant but depending on the frequency.
    In practical terms that means a 4 Ohm speaker could have anything between nearly 0 Ohm and more than 16 Ohm.

    E.g.: Dynaudio Contour 1.3MkII - nominal impedance 4 Ohm, but actually 3.5-14.4 Ohm as stated by the manufacturer.


    You can acheive 4 ohms by wiring two sets of 8 ohm speakers in parallel, getting roughly double the volume.

    ROTFL! Sorry, but that's BS.
     
  10. Reiner

    Reiner
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    What Lynx correctly explains is Ohm's law: U = R*I (Volt = Ohm * Ampere)
     
  11. buns

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    The confusiong is coming with Power = square current times impedence (well for this thread that should be thourough enough) But the fact that the amp still provides the same current is being neglected and the increase in power is simply being assumed to have no opposition.

    As far as the initial question, there may be a slight dgradation in quality because the amp must work harder, but if it is reasonably designed this shouldnt be a problem at all.

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  12. lynx

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    If it's of any interest to anyone,

    OHM'S LAW

    BASE FORMULAS P=I*E E=I*R
    TO FIND VOLTAGE E=P/I E=I*R E=SQR(P*R)
    TO FIND CURRENT I=P/E I=E/R I=SQR(P/R)
    TO FIND POWER P=I*E P=E2/R P=I2*R
    TO FIND RESISTANCE R=E2/P R=E/I R=P/I2


    P = Power in Watts
    E = Electromotive Force in Volts (V=Volts) :blush:
    I = Electrical Current in Amps
    R = Electrical Resistance in Ohms
    SQR = Square Root
     
  13. buns

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    I was informed that we are talking about alternating currents, so should we not be using lower case! :p

    think i'll be a bit more annoying..... i havent ever seen E used in place of V, and normally square root would be sqrt :p

    sorry, couldnt resist! you can get your own back in a onth when i have to know all this and manage to foget! :D
     
  14. bob007

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    ....and I've never seen a blank space used in place of m, typo's are sometimes followed by a pi**take :p :D
     
  15. mjn

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    Actually...it is wrong and it isn't wrong.

    When you have two resistors with static values ie, 8ohms in parallel, then this is correct, but with speakers where the ohm value can change it's incorrect. As the 8ohms of the speakers will be varying.
     
  16. buns

    buns
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    I think the volume was what reiner was laughing at! well, that was what i was laughing at! :D Wishing it was true!

    I didnt use a blank space in place of an 'm'! That is a commonly known text form of the word month, but maybe you best leave that to my generation! :p

    I think all my pypos (look, there is another one!) get the p*** taken, but its just good reason to respond likewise! :D

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  17. Reiner

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    Yep, was refering to the volume thing.


    BTW: in Germay we use "U" for Voltage. "V" is the measure (Volt) of Voltage like "A" (Ampere) is the measure for current "I". And "Ohm" (can't display the 'Ohm' symbol) is used for resistance "R" or impedance "Z".

    Seen SQR before, too, but never "E". Well, actually seen E=mc(square).
     
  18. MikeK

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    What - you've never seen E used to express voltage or (ElectroMotive Force)?

    Bizarre!!


    You can acheive 4 ohms by wiring two sets of 8 ohm speakers in parallel, getting roughly double the volume.

    Actually, strictly speaking, this is quite correct - all things being equal!
    (although it's easy to see why people would think it isn't)


    True, a 4 ohm speaker will not give twice the volume of an 8ohm speaker - as was said, this is primarily decided by the speaker's sensitivity.

    However, if you place one 8ohm speaker on an amp ouput, you'll get a given volume (for arguments sake, say 90dB).
    If you then place another identical speaker in parallel, it will have exactly the same voltage across it and will draw exactly the same current as the first one, and so will also produce the same volume, 90dB. The equivalent impedance seen by the amp will halve (which if the speakers were exactly 8ohm, would now appear as 4ohms total)

    Now, 90dB + 90dB = 93dB

    This 3dB increase is a doubling of the acoustic output (volume?)
    However, we don't hear in a linear fashion.
    It takes a 10dB increase for us to hear an apparent doubling in loudness (also referred to as volume - the terminology is poor, but that's not exactly a new issue).

    That's why I added "strictly speaking" and "all things being equal" :)


    It also assumes a decent amplifier, which won't clip when you halve the load impedance, and will stay linear (ie halve the load impedance, double the output current)
     
  19. mjn

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    didn't i say that in my last post??
     
  20. buns

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    I think the terminology varies somewhat depending upon you field, i know for a fact that my physics notation is somewhat different from that taught to engineering friends.

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  21. MikeK

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    Not quite - it was the bit about

    I think the volume was what reiner was laughing at! well, that was what i was laughing at! Wishing it was true!


    Simply pointing out that strictly speaking, it IS true! :)


    Don't want an argument over it though!! :)
     
  22. Reiner

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    Engineer speaking: a 3dB increase equals to doubling the power output.

    I.e. 30dB = 1W, 33dB = 2W, 36dB = 4W, 39dB = 8W and so on.

    10dB are perceived as doubling the volume and thus require 10x the power (e.g. 1000 Watt instead of 100 Watt).

    So two speakers in parallel may draw twice the current or consume twice the power (as impedance halves), but the volume will not double.
     
  23. mjn

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    lol....yep don't want to argue :)

    i think people just don't fully grasp the all the theory/practice thats all because of all the variations in terminology my manufacturers, etc
     
  24. buns

    buns
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    Of course the prime example being cheapy manufacturers quoting pmpo's and their likes..... My brother still believes his £100 400 watt car amp is more powerful than my thousand pound 30 kilo 50 watt amp! I actually looked at the box and it has small print which says the output is into 2 ohmsdriving only one of 4 speakers....

    i could moan for hours s i'll stop!

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    Ps, anyone fancy installing a big krell in the boot of my car! ;)

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  25. mjn

    mjn
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    lol.....PMPO is the biggest joke ever...all of a sudden, 5w speakers are capable of 300W PMPO and all rubbish like that!!

    All because they quote the peak music power?!?!!?
     
  26. buns

    buns
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    And by the sounds of it, our youth (who are apparently growing ever smarter.....*yeah right*) tend to believe such things! :p

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  27. MikeK

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    Perhaps, but I think we are disagreeing on just a matter of terminology now. :)

    A 3dB increase is double the acoustic power ouput - and acoustic power output is the same as Sound Pressure Level (SPL), which is measured in decibels, as is volume!
    A 10dB increase is double the perceived loudness - this is measured in phons and sones, as is ........volume :) :) :confused:


    I suppose it depends what you mean by volume at the end of the day - I was just pointing out that the original poster was right - from one perspective :) :)
     
  28. Reiner

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    lol.....PMPO is the biggest joke ever...all of a sudden, 5w speakers are capable of 300W PMPO and all rubbish like that!!

    Yeah, and that from 6 AAA batteries. :D

    @MikeK: ok, understood and point taken. :)
     
  29. buns

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    terminology is there to confuse us, if we werent conused by it, we'd be using it wrong! :D

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