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gmorris
gmorris Posts: 1,179
edited July 2003 in Basic Hookup/Wiring Questions
Here is a question I've always wondered about. Maybe someone here on the forum know about this kind of thing.

If a lower ohm load shown to an amp means more power, can you wire some kind of device (resistor, capacitor, ect...) in line with your speaker to lower the effective nominal ohm rating of the speaker?

Example: The speaker is rated 8 ohms nominal. You wire some device in line with the speaker to make the load seen by the amp 6 ohms. More power is delivered to the speaker. (maybe?)

Again, I know nothing about electrical engineering. Is this possible? What would be the side effects of doing this?


Late,
Greg
Bob Mayo, on the keyboards. Bob Mayo.
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  • HBombToo
    HBombToo Posts: 5,256
    edited July 2003
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    Its an intuitive thought but there is more to it than that. To lower your impedance you would have to hook up the resistor in parallel. Now, in a parallel network the current will split across the 2 network paths and in effect you would have less power driving your speaker at the same voltage.

    Example:

    an 8 Ohm resistor in Parallel with an 8 Ohm speaker will now give you 4 Ohms. Holding your voltage as a constant you have 1/2 the current through the speaker so in effect 1/2 the power applying P=V*I or in this case P=V*(1/2)I

    Hope this helps.

    HBomb
    ***WAREMTAE***
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  • Eastern
    Eastern Posts: 43
    edited July 2003
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    If you hook up a resistor in parallel to the speaker, in the simplest sense, there will not be any increase or decrease in power to the speaker. The basic equations are :

    I = current
    V = voltage
    R = resistance
    P = power

    V=IR
    P =IV

    As an example, for a typical AMP, if you half the impedance, it will crank out double the power by doubling the voltage across the resistive elements to keep the current through each resistor the same. (High current AMPS only -- THAT'S WHY NOT ALL AMPS ARE EQUAL. The load sensing circuitry is what makes or break the AMP more that anything else.)

    However, the power is burned up in 2 different resistors so in effect, the power burned in each resistor is the same. This analysis works for resistors. However, when you factor in the speakers which have dynamic impedance depending on frequency, you run into some problems.

    As an example, a speaker that is rated as 8 ohm nominal may only be 2 ohm at 20Hz. But since you have placed an 8 ohm resistor in parallel to it, the net impedance (dynamic resistance) is 1.6 ohm (not the 1 ohm that you intended)

    Now say at 15 KHz, the resistor is still 8 ohm, and now the speaker may be 12 ohm at this frequency, the net impedance becomes 4.8 ohms (not the 1 ohm you intended)

    This occurs for all frequency spread, so what happens is that you have just introoduced distortion into the system and made the AMP work a lot harder than it should to produce approximately the same power to the speaker but with more distortion.

    However, if instead of hooking up a resistor in parallel, you hook up an inductor (or capacitor) then the circuit changes again. How you have 2 new parameters to play with depending on frequency.

    A Capacitor's impedance decreases with higher frequency and the opposite is true for an inductor. (this is the basis for filters and speaker design)

    Now if you were to hook up an impedance matched speaker in parallel to the current speaker, then YEAH! you do get more SPL. But this is the only way. And not that it has to be impedance matched (like exactly the same speaker) or you will cause interaction between the 2 speakers (filters aka crossovers) to cause distortion.
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  • HBombToo
    HBombToo Posts: 5,256
    edited July 2003
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    something like that.... Eastern, I'm the twin right now and don't care to debate!

    ET
    ***WAREMTAE***
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  • Eastern
    Eastern Posts: 43
    edited July 2003
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    HBombToo, didn't mean to debate anything, just sharing what I know. I realized I have a few typos in there. Anyway...

    Cheers..
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  • PhysicsCoder
    PhysicsCoder Posts: 40
    edited July 2003
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    Hmm. Well, I was all set to say stuff about impedance, frequency dependance, and maybe even phase shifting, but it seems that Eastern has beat me to it. :)

    Bottom line: I agree with Eastern and HBomb. Don't put a resistor(or even an RLC curcuit) into the speaker line. It won't give you any more power from the speaker, it may distort the sound that's already there, and it may even overload yer amp.

    My $0.02
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  • Tour2ma
    Tour2ma Posts: 10,177
    edited July 2003
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    Eastern,

    First welcome to the Club... I, and at least one of the "twins", welcome another member that understands circuits...

    I think the short answer here was, "Won't help". Adding an artificial means of dropping the apparent impedance will produce no benefit and in fact could harm a low current amp and the speakers it attempts to drive. i.e., induce clipping.

    Now a second pair of speakers in parallel... different matter. Dangers still exist, but at least there is a potential upside.

    Only statement with which I'll take minor exception is, "for a typical AMP, if you half the impedance, it will crank out double the power." This kind of amp performance is still not the norm as most amp specs will indicate. The current proviso does qualify this to some extent, but even some amps that can be considered "high current" fall short of doubling when the load is dropped from 8 to 4 ohm.

    EDIT - Damn.... took a couple weeks off for typing lessons and still can't live without spell check... :rolleyes:
    More later,
    Tour...
    Vox Copuli
    Better to remain silent and be thought a fool, than to open your mouth and remove all doubt. - Old English Proverb

    "Death doesn't come with a Uhaul." - Dennis Gardner
    "It's easy to get lost in price vs performance vs ego vs illusion." - doro
    "There is a certain entertainment value in ripping the occaisonal (sic) buttmunch..." - TroyD
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  • HBombToo
    HBombToo Posts: 5,256
    edited July 2003
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    Originally posted by Tour2ma
    Eastern,

    First welcome to the Club... I, and at least one of the "twins", welcome another member that understands circuits...

    Ya know Tour... You are absolutely correct and I also want to welcome Eastern.



    HBomb
    ***WAREMTAE***
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  • Tour2ma
    Tour2ma Posts: 10,177
    edited July 2003
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    :lol:... but sooner or later "ET" pops up... :)
    More later,
    Tour...
    Vox Copuli
    Better to remain silent and be thought a fool, than to open your mouth and remove all doubt. - Old English Proverb

    "Death doesn't come with a Uhaul." - Dennis Gardner
    "It's easy to get lost in price vs performance vs ego vs illusion." - doro
    "There is a certain entertainment value in ripping the occaisonal (sic) buttmunch..." - TroyD
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  • HBombToo
    HBombToo Posts: 5,256
    edited July 2003
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    Originally posted by Tour2ma
    :lol:... but sooner or later "ET" pops up... :)

    I hear ya... Later ET will pop in.
    :D

    but first Gonna tear my rig apart and give it a thorough GI!

    Even bought a new jar of acetone for the conections.

    HBomb
    ***WAREMTAE***
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  • Tour2ma
    Tour2ma Posts: 10,177
    edited July 2003
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    ... Inhale deeply and no smoking... could unleash a long hinden triplet... :)

    BTW nail polish remover is acetone...

    Also just posted a St. Louis, ebay, SRS siting in FM...
    More later,
    Tour...
    Vox Copuli
    Better to remain silent and be thought a fool, than to open your mouth and remove all doubt. - Old English Proverb

    "Death doesn't come with a Uhaul." - Dennis Gardner
    "It's easy to get lost in price vs performance vs ego vs illusion." - doro
    "There is a certain entertainment value in ripping the occaisonal (sic) buttmunch..." - TroyD
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  • Eastern
    Eastern Posts: 43
    edited July 2003
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    Thanks for the welcome people.:)

    Question -- Who's one of the "twins" ?

    Cheers
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  • Tour2ma
    Tour2ma Posts: 10,177
    edited July 2003
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    You're welcome for the welcome(s)...

    HBomb is both the twins... dual personality thing... so far there are only two that we know of... ;)
    More later,
    Tour...
    Vox Copuli
    Better to remain silent and be thought a fool, than to open your mouth and remove all doubt. - Old English Proverb

    "Death doesn't come with a Uhaul." - Dennis Gardner
    "It's easy to get lost in price vs performance vs ego vs illusion." - doro
    "There is a certain entertainment value in ripping the occaisonal (sic) buttmunch..." - TroyD
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  • HBombToo
    HBombToo Posts: 5,256
    edited July 2003
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    Originally posted by Tour2ma
    ... Inhale deeply and no smoking... could unleash a long hinden triplet... :)


    I think Russman met the Triplet the other night on the phone.:D

    It was a needed marathon event which got me in trouble because I polished off 1.5 bottles of the wifes wine when I finished my 12 pack and rum. I was a hurt puppy the next morning.

    HBomb is starten his Twin act!:p after dealing with all those guzintas and comzoutaz.

    Halfway through the project I was thinking about a bose settup;)

    HBomb
    ***WAREMTAE***
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  • goingganzo
    goingganzo Posts: 2,793
    edited July 2003
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    but you can look at the cross over they have resistors that change the xo and can also afect the ohm rateing so you can allways drop the r of the speaker but you will change the charestic of the speakers performance.
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  • TroyD
    TroyD Posts: 13,077
    edited July 2003
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    To the new guys....welcome!

    To Russ, HBomb and Tour......SCREW YOU GUYS! HA!

    BDT
    I plan for the future. - F1Nut
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