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Ohm question

This is a discussion on Ohm question within the Stereo and Electronics forums, part of the General Help category; Okay, with subwoofers I know how wiring works. With coaxial/component speakers, I'm not so sure. I do know that, were ...

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    Ohm question

    Okay, with subwoofers I know how wiring works. With coaxial/component speakers, I'm not so sure. I do know that, were both speakers subwoofers, they would have to each represent a load of 8 ohms to run in parallel at the amp's desired resistance of 4 ohms. However, it seems relatively common for both speakers in a component system to be 4 ohms, causing a load of 2 ohms on the amp when they're wired in parallel and crossed over independently.

    I recently ran a 4 ohm speaker in parallel with a 6 ohm tweeter and there were no problems - but what's the ohmage load? Is there a possibility that it's somewhere between 4 and 6 because the speaker goes up to about 2500 hz and then the tweeter kicks on at 8k and there is no overlap? Or does it matter? I've noticed that many times on home speaker systems they will run 3 seperate 8 ohm speakers in parallel and then claim total impedance for the speaker as 8 ohms - which wouldn't be true at all for 3 subwoofers! What's the deal?


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    Member fieropope's Avatar
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    the only difference is if you run one speaker at 4 ohms and one at 6 ohms in parallel the 4 ohm speaker is going to get more power .the speaker with the least resistance(ohms) is going to be the loudest.some times like in the case of subwoofers it can lead to the amplifier heating up too fast and shorting out. Just for future reference ohms in a parallel circuit is less than the smallest resistor (speaker).EX if you have two 6 ohm speakers in parallel the actuall resistance is found like this(6x6) divided by (6+6)or (sp1xsp2)div(sp1+sp2).
    actuall resistance in the circuit is 3 ohms. hope this helps

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    That guy thearborbarber's Avatar
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    Also the ohm rating on a speaker is it's impedence rating not it's resistance value. If you measure a speaker's terminals with a volt/ohm meter you will get zero ohms. a speaker is wire wound around a magnet connected to a cone. Impedence takes into account frequency and stuff life that. Having a miss mathced speaker and amp is like having a cb radio with a miss matched antenna.

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    Quote Originally Posted by thearborbarber View Post
    Also the ohm rating on a speaker is it's impedence rating not it's resistance value. If you measure a speaker's terminals with a volt/ohm meter you will get zero ohms. a speaker is wire wound around a magnet connected to a cone. Impedence takes into account frequency and stuff life that. Having a miss mathced speaker and amp is like having a cb radio with a miss matched antenna.
    Very interesting. Could you tell me a little more about how the frequency is taken into account? I've built crossovers and a few things like that before so I know that for example a 4 way coaxial speaker system may have 3 different tweeters but for the most part it's only going to have one or two high pass filters and above the highest frequency value they all carry the same freqs too. So if I'm going to try to even these two out what should I do? 2 ohm resistor on the 4 ohm speaker in my system? It also strikes me I could simply run them on seperate channels.

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    d'oh!

    maybe d'ohm would be funnier? rofl

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    Quote Originally Posted by thearborbarber View Post
    Also the ohm rating on a speaker is it's impedence rating not it's resistance value. If you measure a speaker's terminals with a volt/ohm meter you will get zero ohms. a speaker is wire wound around a magnet connected to a cone. Impedence takes into account frequency and stuff life that. Having a miss mathced speaker and amp is like having a cb radio with a miss matched antenna.
    no you hook a dmm up to a sub you get an ohm reading buddy unless it's blown

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    Quote Originally Posted by wenn_du_weinst View Post
    no you hook a dmm up to a sub you get an ohm reading buddy unless it's blown
    so tweeters and mids, for the most part, just have so much less wire in them that their resistance corresponds pretty much only to volume of sound produced? I take it identical drivers produce the same impedance so that's why you want identical subs if you're doing several in the same box, and with regard to the original question you can use pretty much whatever tweets and mids you want wired in parallel and it will be ok because they don't suck up much power?

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    any speaker wired in parallel will sound the same as the others but that kinda defeats the purpose of having mids and tweets in that case you should just have a bunch of mids in your car

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    Member fieropope's Avatar
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    and yes the ohm reading is there when the speaker is under power using a different equation the actual resistance can be found. "When the circuit is driven with direct current (DC) there is no distinction between impedance and resistance; the latter can be thought of as impedance with zero phase angle." this means there is no difference between impedance and resistance when used in a car stereo(DC current)
    Last edited by fieropope; 09-23-2009 at 05:11 PM.

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    Member wenn_du_weinst's Avatar
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    Quote Originally Posted by richard head View Post
    so tweeters and mids, for the most part, just have so much less wire in them that their resistance corresponds pretty much only to volume of sound produced? I take it identical drivers produce the same impedance so that's why you want identical subs if you're doing several in the same box, and with regard to the original question you can use pretty much whatever tweets and mids you want wired in parallel and it will be ok because they don't suck up much power?
    diference is tweeters and mids don't play the same frequency as each other 2 subs do plus high frequency doesn't cancel out as much as bass notes do

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    Quote Originally Posted by wenn_du_weinst View Post
    diference is tweeters and mids don't play the same frequency as each other 2 subs do plus high frequency doesn't cancel out as much as bass notes do
    well a lot of the freqs that mids and tweets do are the same though. oh well i understand the point. thanks for the help.

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