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Thread: impedance ohm question

  1. #1
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    impedance ohm question

    HY,

    I will like to know how to calculate the impedance of a loudspeaker 3 ways:low,mid,high drivers? Let's say that I have a woofer 8 ohm
    a mid 4 ohm and
    an high driver 16 ohm


    What will be the "resulting" impedance of this loudspeaker driven with a single stereo amplifier (no bi or tri amplified).

    Thank You, Robert

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    Senior Member louped garouv's Avatar
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    i'm no expert, but i think the impedance of each driver will change over the freq. reproduction demands seen each said driver...

    here's a thread somewhere else that talks this...

    http://www.audiokarma.org/forums/showthread.php?t=99749

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    Senior Member jcrobso's Avatar
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    Sperkaer impedance is a complex issue.

    Quote Originally Posted by pluton123 View Post
    HY,

    I will like to know how to calculate the impedance of a loudspeaker 3 ways:low,mid,high drivers? Let's say that I have a woofer 8 ohm
    a mid 4 ohm and
    an high driver 16 ohm


    What will be the "resulting" impedance of this loudspeaker driven with a single stereo amplifier (no bi or tri amplified).

    Thank You, Robert
    The one item that you are leaving out is the crossover network. each section of the crossover network work have to be designed for each speaker. The low pass section would be for a 8 ohm woofer, the band pass for a 4 ohm mid range and the high pass section of a 16 ohm tweeter.
    By the time you did this and put it all together you would have about a 2.8 ohm impedance load

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    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by pluton123 View Post
    What will be the "resulting" impedance of this loudspeaker...
    First of all, there is no such thing as an 8 ohm or 4 ohm loudspeaker. If you've ever read a review of a speaker where they do technical measurements you will see a graph of the system's actual impedance. Typically a "4 ohm" loudspeaker will not dip below 4 ohms and it is therefore called 4 ohm... every speaker and every driver will exhibit a different impedance at every frequency, but it gets much more complicated than that.

    Read this:

    http://www.stereophile.com/reference/707heavy/


    Widget

  5. #5
    Senior Member grumpy's Avatar
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    in using a crossover to send the "proper" frequency range to each speaker, you are
    also allowing the amplifier to "see" the impedance of each driver within it's intended
    operating range.

    If it were as simple as the woofer being "8 ohms", the midrange "4 ohms" and the
    tweeter "16 ohms", you might have a resulting system that showed a series of steps
    (down, then up) in plotting impedance vs. frequency. One then might take the simple
    notion that ensuring the amp can drive 4 ohms would be safe.

    Unfortunately, a woofer is not "8 ohms", other than over a (sometimes small) range
    of frequencies. For example, it might measure 5 ohms using an ohm meter (measuring
    at DC), 60 ohms at resonance, and then drop back down to ~8 ohms for awhile, then
    start increasing again. The mid and tweeter can have frequency dependent
    impedance as well.

    Add in a crossover (well-designed or otherwise) and it gets more complicated.

    Point is, that it's not enough to put nominal 8,4,16 ohm together as though they
    were parallel resistors and come up with one single value.

    On a practical note, using the 4-ohm-safe amplifier is reasonably cautious, but
    likely overly so... much music has more energy in the "woofer" region and
    usually "works" the amplifier harder than in the midrange, so using an amp intended
    for 8 ohms may not be such a big concern for home listening anyway.

    Confusing enough? Here's an article with pictures:

    http://www.stereophile.com/features/99/index5.html

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    Senior Member grumpy's Avatar
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    Heh... just saw Widget's post. Pretty funny. I type too slowly.

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    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by jcrobso View Post
    By the time you did this and put it all together you would have about a 2.8 ohm impedance load



    Depending on the design of the crossover and the actual impedance curves of the drivers, the minimum impedance could be almost anything.

    Quote Originally Posted by grumpy View Post
    Heh... just saw Widget's post. Pretty funny. I type too slowly.
    Yeah, me too.


    Widget

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    Administrator Robh3606's Avatar
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    Hello Robert

    What Widget said. What you would need is a complete schematic of the crossover and driver imp curves. Then you need software to look at it all together. Unfortunately there is no simple answer. Something as simple as taking out a resistive pad can have a major effect.

    Rob
    "I could be arguing in my spare time"

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    impedance ohm question

    Thank You ALL !!!

    Robert,

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    Quote Originally Posted by Mr. Widget View Post
    First of all, there is no such thing as an 8 ohm or 4 ohm loudspeaker. If you've ever read a review of a speaker where they do technical measurements you will see a graph of the system's actual impedance. Typically a "4 ohm" loudspeaker will not dip below 4 ohms and it is therefore called 4 ohm... every speaker and every driver will exhibit a different impedance at every frequency, but it gets much more complicated than that.

    Read this:

    http://www.stereophile.com/reference/707heavy/


    Widget
    So are you saying there is such a thing as a 16 ohm speaker?

    Allan.

  11. #11
    Administrator Mr. Widget's Avatar
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    Smart ass!

    "Full Range" ribbons tend to have purely resistive loads (impedances) and are an exception to the discussion above... 16 ohm speakers notwithstanding.


    Widget

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    Quote Originally Posted by pluton123 View Post
    ...with a single stereo amplifier...
    In addition to all the guidance here, watch the expected load your "stereo amplifier" can handle. You posts sounds like you are referring to a consumer grade amp - most of those are happiest with an 8-ohm load, maybe 4-ohm if you have two sets (A + B) of 8-ohm speaker cabinets running.
    bo

    "Indeed, not!!"

  13. #13
    Senior Member duaneage's Avatar
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    I'll also add the type of enclosure the woofer is in greatly affects the shape and amplitude of the impedance around resonance. Vented boxes have two peaks whereas sealed enclosures have one. A vented bandpass will have a radically different set of curves from a sealed bandpass. Passive radiator systems like the L150 typically have 3 impedance peaks.

    A good high quality amplifier should be able to handle these scenarios, although connecting two or more pairs together might produce unusual loads. It is possible to determine the real impedance with a voltmeter, frequency counter, fixed resistor and frequency generator. Phase angles and other components of the load are more complicated, there are meters for that but they run about 600 dollar or so.

    Sealed speakers are safest to run in pairs since they have simple impedance curves and are likely not to run too low.
    Why buy used when you can build your own?

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    Senior Member sbjacob's Avatar
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    Quote Originally Posted by pluton123 View Post
    HY,

    I will like to know how to calculate the impedance of a loudspeaker 3 ways:low,mid,high drivers? Let's say that I have a woofer 8 ohm
    a mid 4 ohm and
    an high driver 16 ohm


    What will be the "resulting" impedance of this loudspeaker driven with a single stereo amplifier (no bi or tri amplified).

    Thank You, Robert
    Klipsch uses a 4 ohm woofer a 16 ohm mid and a 8 ohm tweeter in there La scalas ,Klipschorns , Cornwalls and Heresys.Here is a basic crossover schematic they used.The crossover points are 400 and 4500.Name:  Picture 008.jpg
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