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Speaker impedance - explain?

Discussion in 'Electronic Basics' started by andrew_h, Feb 19, 2006.

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  1. andrew_h

    andrew_h Guest

    Can someone explain to me exactly what speaker impedance is?

    Also, Why is it only 4, 8, etc. ohm? (such even numbers).
     
  2. Phil Allison

    Phil Allison Guest


    ** NO.


    ** NO.


    Do a Google search you lazy piece of shit.




    ......... Phil
     
  3. andrew_h

    andrew_h Guest

    I have....is confusing.
     
  4. andrew_h

    andrew_h Guest

    Actually I ask is on this board because when an actual person explains
    it, it makes alot more sense.

    Some of the 'tutorials' and 'faqs' on the net are unneccessarily
    complex.
     
  5. Phil Allison

    Phil Allison Guest

    "andrew_h"


    ** First off - learn to use "googlegroups" correctly.

    Do NOT simply hit reply !!!!!!!!!!!!!!

    Hit "options" and then "reply".

    That way we can see who you are replying to and about what.



    ** Basically, it is the resistance of the coil of copper wire inside.


    ** Speakers with impedances from 0.5 ohm to 1000 ohms have been made.

    The range from 4 to 16 ohms is just *much* easier to make.

    In the valve era, 2 ohms was common for radio set speakers and 16 ohms for
    early hi-fi speakers.

    The most common by far now is 8 ohms, since it suits power transistor
    voltage and current abilities best.

    Two 16 ohm speakers in parallel gives 8 ohms.

    Two 8 ohm speakers in parallel gives 4 ohms.

    It is just that simple.



    ........ Phil
     
  6. Pooh Bear

    Pooh Bear Guest

    How about starting with this response ?

    Do you know the difference between resistance and impedance ( of
    anything ) before launching into an elaborate discussion of same.
    It isn't. 4, 8, 15/16 are simply commonly accepted norms. 6 ohms isn't
    uncommon either in some kit. Don't forget that the impedance is simply
    'nominal'.

    Graham
     
  7. Pooh Bear

    Pooh Bear Guest

    I know. Some ppl like to 'show off' and 'miss the point'.

    Graham
     
  8. andrew_h

    andrew_h Guest

    Thanks for all your replies.

    I did search alot on google before - but yeh, alot of people like to
    read their own words, and so the descriptions arent as simple as they
    can be.

    Once something is understood, it then becomes very easy - thats why
    people who know about a topic alot will think everything is easy to
    understand.
     
  9. Bob Masta

    Bob Masta Guest

    First of all, instead of "impedance" think "AC resistance".
    It's the value you would use when you are trying to compute
    the power the speaker will draw from the amp, via V^2/Z
    where V is the RMS output voltage and Z is the impedance.

    (Note that the power drawn by the speaker is not the
    same as the sound power delivered, since speakers
    have a wide range of efficiencies... but 1% is typical.)

    In a speaker, impedance is made up of the DC resistance
    of the copper wire in the voice coil, plus the AC "reactance"
    of the inductive effects from that same wire being in the
    form of a coil (with an iron core), plus the mechanical
    reactance due to the spring in the suspension and the
    mass of the moving cone. The reactance part varies
    with frequency, and actual speaker impedance typically
    has a big peak around resonance, or two peaks one
    on either side for tuned designs (like those with ports
    or passive drivers).

    So, the numbers like "4 ohms", "8 ohms", etc are
    really just nominal values. Their main real use is
    in comparing suitability of drivers for use with a
    particular amp. Higher impedances demand less
    current from the amp to get a certain power, so
    amps are typically rated as to the lowest nominal impedance
    they are happy to drive. Lower impedance may
    draw too much current, but you can always use
    a higher impedance speaker... at least with modern
    solid state amps. Tube-type amps with output
    transformers typically have different taps for driving
    different speaker impedances, and there you
    should select the matching value.

    Best regards,



    Bob Masta
    dqatechATdaqartaDOTcom

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
    Home of DaqGen, the FREEWARE signal generator
     
  10. Jamie

    Jamie Guest

    its the same as it would be if you were
    to calculate DC resistance except with
    the term impedance, it normally indicates
    that an AC signal is involved and under
    these conditions some devices behave differently
    giving you a different results of resistance
    over what would be Dc ohms.
    for example, a speaker coil can be inductive
    and thus at high frequencies the impedance of the
    circuit may increase. that is one reason among
    others that it is good to have a multiple set of
    speakers attached to the output that covers all
    ranges of audio.
    but in most practical mid range type speakers you
    will find the impedance matching very close to what
    a DC ohm reading is.
     
  11. Jamie

    Jamie Guest

    P.S.
    one more thing.
    the lower ohm type speakers are normally used in low voltage
    systems where it saves on cost of an amplifier to drive the
    voltage up that will thus deliver enough power to satisfy your
    needs for volume.
    in the case of automobiles for example, 12 volt systems can
    only generate a limited amount of Db's from a speaker using lets
    say a 8 ohm system how ever, if you were to use a 4 ohm system
    you can then get double the output as long as the components can
    handle the current.
    2 ohms systems even get more current in the speaker coil from a
    12 volt amp..
    then you have those amps that have power inverters in them so that
    the internal power voltage level is actually higher than the supply
    line. these normally draw more current depending on how much higher the
    increase of voltage is.
    these low ohm speakers are great and solves issues of getting more
    dbs from a speaker with lower voltage equipment how ever, it also adds
    to the cost of larger gauge wire for long runs. this is why higher ohm
    speakers are popular in some areas. long runs of small gauge wire with
    higher voltage
    amplifiers reduces the needs for larger gauge wire.
     
  12. Ross Mac

    Ross Mac Guest

    Well explained Bob couldn't have done better myself.....that ought to end
    this thread!
    .....Ross
     
  13. unbiased

    unbiased Guest

    Horrible manners. This IS sci.electronics.basics. People might
    actually discuss and help instead of being rude.
    <plonk>
     
  14. Ignore Phil. He suffers from a form of autism known as Asperger's
    Syndrome which means he's incapable of communicating effectively with
    the outside world.
    Your question's a very good one. If I hadn't drunk a bottle of
    Australian wine this afternoon, I'd happily answer it. Hopefully,
    however, someone else will. :)
     
  15. Phil Allison

    Phil Allison Guest

    "Paul Burridge"

    ** Ignore Paul Buggerage.

    The vile pommy cretin suffers from a form of autism known as Asperger's
    Syndrome which means he's incapable of communicating effectively with
    the outside world.





    ......... Phil
     
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