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ohms and impedence

Discussion in 'Beginners, General Questions' started by Shawn_M, May 22, 2004.

  1. Shawn_M

    Shawn_M Member

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    ok guys this may be dumb but can someone explane the whole ohms impedence and resistance to me or point me somewhere i can find some info on this i know a little but still a little cloudy on the whole thing
     
  2. Frank Zimkas

    Frank Zimkas Well-Known Member

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  3. Vince Maskeeper

    Vince Maskeeper Well-Known Member

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  4. Iver

    Iver Well-Known Member

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    This site explains electronic theory in pretty straightforward language. It also has links to information on amateur (ham) radio. Getting an FCC license, either amateur or for commercial broadcasting (the underlying theory is the same for both) is a great way to really learn practical, real-world electronics.

    http://www.electronics-tutorials.com/


    This is the section where you will find Ohm's Law, the key to understanding the interrelationship between resistance, voltage, current, and power:

    http://www.electronics-tutorials.com...lectronics.htm
     
  5. Allan Jayne

    Allan Jayne Well-Known Member

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    It is difficult to define "ohm" (or volt or ampere for that matter) in an absolute sense without getting into deep scientific detail including numbers of electrons.

    But in a relative sense, speaker A rated with twice as many ohms (has twice the impedance) as speaker B would behave (in terms of amplifier loading, not sound quality) about the same as two of speaker B connected in series.

    Also in a relative sense, a speaker (or other device) has one ohm if, when a one volt power source is applied, one ampere flows. Ohms law states that the following is always true in any electrical circuit at all times, volts equals amperes times resistance in ohms (or impedance in ohms).

    I didn't say exactly the same because impedance varies with frequency and different speakers with rated impedance (at 1000 Hz) may have a different impedance versus frequency characteristics (as may be graphed).

    Resistance, also measured in ohms, is for direct current.

    The importance of matching amplifier impedance to speaker impedance is that, if you don't, the frequency response of the amplifier may be incorrect. I am not sure what the meaning of amplifier impedance per se is. Any amplifier will overload and possibly burn out itself, the speakers, or both, if you turn the volume up too high. It is not easy to determine all the conditions when overloading is taking place although distorted sound is one condition you can easily detect.

    If you keep the volume low, you can get away with connecting a "higher" impedance amp to a "lower" impedance speaker. Here, overload conditions that you cannot detect with your ears are more likely to occur at louder volumes. Generally the number of volts (unseen to you) versus the volume setting (e.g. knob at 10 o'clock or bar graph at 40% etc.) is the same with the amp. and, for example if the speaker has half the impedance, twice the number of amperes flow so you hit the amplifier power limit sooner.

    Speaker efficiency (loudness as you hear it versus number of amperes of amplifier power) varies widely and there is no rule that higher (or lower) impedance speakers are more efficient.

    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     

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