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Thread: How many ohms did I win?

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    Cool How many ohms did I win?

    G'day All,

    Messing with a Heinz 57 car stereo just wondering if anyone might know what sort of ohm load the following might produce.

    A rather rough diagram below showing how I currently have it wired inside the doors, speaker connections not hooked up to the amp yet.
    It will be running 2 separate speaker lines to each door paralleled from the amp, the 6x9 will be on one line by itself and I'm planning to have the 2 drivers and tweeter on the other, unless there's a better way to wire it.

    The two 6 inch JVC drivers I wired in sequence, but I doubted the tweeter (sealed up inline crossover/resistor/whatever) would handle all the return current back to the amp if it was also in that same sequence, so I piggy backed it's positive from the first driver, and it's negative just hooks back into the main earth return to the amp.

    The 6x9 and the two JVC 6 inch drivers are 4 ohm rated.
    Each 6 inch driver came with a split tweeter, two of which are dead so it'll just be the one split tweeter in each door.
    I have no idea what impedance the tweeters are rated at as there's nothing on them at all and I don't really want to remove the factory heat shrink from the inline crossovers as they'll likely fall to bits
    The amp is 2 ohm - 4 ohm stable according to it's service manual, an old Alpine MRV-T300.
    Not really enough space for another amp to separate the wiring so decided I'd have a go at things with this one.
    Thought it might pay to ask before I connect it all and start running it to perhaps save something getting fried.

    Thanks


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    LSemmens
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    In series the resistance is additive so 8(ohnms) + 8 = 16ohms
    in parallel the calc = 1/8 + 1/8 = 2/8 = 1/4 = 4ohms
    don't forget the power to drive them could also be an issue
    as two 40W speakers are going to need 80W to drive them.

    looking at your diagram the two speakers lower left and upper right won't work at all as you have connected straight across both terminals. In fact, you might even blow your amp as there is a short across the + and - on the top right speaker. You might be best letting a pro set up what you desire as we have no information about what is driving this setup or what you are hoping to achieve.
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    Thanks, yes I'm aware of the extra power requirements, the doubling of power is required to run at maximum rms output when wired in series, which isn't required here, my aim is to get a setup where the ohms are at a level the amp is stable at.

    There will be no short there, that's how speakers are wired in series.
    The positive from the amp goes to the positive on the first speaker, then the negative from that first speaker goes to the positive on the next speaker and so on, the negative from the last speaker in the series goes back to the negative on the amp.

    Decades ago when messing with car stereos we used to run 2 x 4 ohm subwoofers in series if the amp being used wasn't 2 ohm stable, which worked fine.
    Running 2 x 4 ohm subwoofers in parallel drops the ohms by half, to 2 ohms.
    I believe if I wire everything I have in parallel I'll end up with a load of around 1-ish ohms, which the amp won't handle.
    So decided to experiment with a combination of parallel and series wiring for the different speakers and that being paralleled from the amp

    More curious about the actual ohms I'd end up with with what I've already got than anything.


    Last edited by Jma; 04-06-24 at 04:09 PM.
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    Quote Originally Posted by Jma View Post
    There will be no short there, that's how speakers are wired in series.
    Not according to your first diagram.

    lsemmens is correct.

    You have a (red) wire bridged across both positive and negative terminals of the two JVC speakers.

    So according to that diagram the 6X9 speaker on one channel is 4 ohms and the channel with the two JVC's & tweeter will be 0 ohms (due to the short).
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    Yeah I probly screwed the diagram up, was done in a hurry.
    Should be green after the lower speaker's positive terminal perhaps?

    It's wired so nothing goes from positive to ground without first running through a speaker.

    The wiring for the 2 x 6 inch JVC's goes like this:
    Positive speaker output from the amp goes into the lower speaker's positive terminal.
    Next, from the positive terminal on the lower speaker, it loops around onto the negative terminal on the same/lower speaker, not grounded.
    Then from the negative terminal on the lower speaker it goes into the positive terminal on the upper speaker.
    Then from the positive terminal on the upper speaker it loops around onto the negative terminal of the same/upper speaker, not grounded.
    Finally, from the negative terminal of the upper speaker it runs back onto the speaker negative of the amp where it's all grounded through the amp.

    The tweeter is wired like this:
    It's positive input comes from the positive terminal of the lower speaker, through it's inline crossover/resistor onto the positive terminal of the tweeter.
    It's negative terminal wire (not looped from it's positive) shares the single earth wire running back to the negative on the amp.

    If it doesn't work wired like that I will probably try removing the tweeter from the series the 2 x JVC's are on and piggy back the tweeter's positive and negative from the relevant terminals of the 6x9.
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    If wired in series, two 8 ohm speakers will be 16 ohms yes, positive from amp to positive of spkr 1 negative of spkr1 to positive of spkr 2, negative of spkr 2 tro negative of amp.

    If wired in parallel, two 8 ohm speakers will be 4 ohms. positive from amp to positive of both spkrs and negative of amp to negative of both speakers.
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    Yep that's how it works, easy to calculate for dual speaker setups that have the same ohms and wiring from the amp or source.
    Not so easy when it's run as parallel out from the amp into a mixture of separate standard and series wirings for each side.

    Testing the resistance ohms with a multi-meter when everything's joined like it'll be connected to the amp, I get consistently 2.8 ohms from each door at the end of the speaker wires where they'll be hooked to the amp.
    May work may not, 4 channel amp would sure make it a lot easier but anyway...
    Resistance ohms are a single measurement taken via direct current, whereas impedance ohms I believe are alternating current and vary with the frequency of the music, the higher the frequency, the higher the ohms.
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    Apologies for my ignorance.

    I just pulled the skin off a door again to see what I actually did to be sure I hadn't messed it all up.
    Seems I got it right in the car but everything in this thread wrong, the diagram above is wrong for the 6 inch JVC's and my description of how I wired them is also wrong, 6x9 part of the diagram is correct, no idea where I got the "loops around" BS from on the diagram or description, perhaps a long distant memory from wiring up dual voice coil subs to get the right impedance for certain amps or something...

    I hate getting old

    The JVC's:
    Positive speaker output from the amp goes to the positive of the lower speaker.
    From the negative terminal of that same lower speaker it runs to the positive terminal of the upper speaker.
    From the negative terminal of the upper speaker it runs back to the negative on the amp where it's grounded.

    Tweeter is correct in diagram and description, it's positive input comes from the positive terminal of the lower speaker, through it's inline crossover/resistor onto the positive terminal of the tweeter.
    It's negative terminal wire shares the earth wire running back to the negative on the amp.

    How the diagram should look:

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    That will work.
    I'm out of my mind, but feel free to leave a message...

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