# ohms law failed? =O



## swong46 (Feb 15, 2010)

Ok, well ohms law didnt really fail but I have a pair of car audio component speakers that are 4 ohm each.

I wired the crossover input wires in parallel and got a 2 ohm load. When I wire it in series, it is still 4 ohm, not 8 ohm...

Any help?


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## Syd26147 (Jul 4, 2008)

If you don't mind my asking how did you measure the impedance?

SYd


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## swong46 (Feb 15, 2010)

with a multimeter set to 200 ohms range

each comp separately was 4.3 ohms
series was 4.6 ohms
parallel was 2.3 ohms


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## Syd26147 (Jul 4, 2008)

You are reading DCR ( DC resistance ) not impedance.
This is a common mistake.
AC and impedance involve the addition variables of frequency and phase.
DC resistance is commonly 60 - 80% of impedance.
But speakers are reactive elements, so their impedance varies with frequency.
Often impedance values are stated at a given standard frequency of 1000Hz.

Syd


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## swong46 (Feb 15, 2010)

But how come when I measure my subs in DC, it reads like normal?
And how could I measure actual impedance?


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## Syd26147 (Jul 4, 2008)

This may help
Here is a representative link 
http://www.installer.com/tech/sit.html
That's the old school method
Nowadays I use WTII to measure impedance.

Syd


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## swong46 (Feb 15, 2010)

So, can I just hook up the speakers to my receiver and play a certain sine frequency and then measure the ohms? or will that somehow mess up the receiver?


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## lcaillo (May 2, 2006)

The resistive component should still add. You are either not wiring in series like you think or you are measuring at the wrong points. You may also have a load in the crossover altering your reading.


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## swong46 (Feb 15, 2010)

both crossovers have tweets and mids attached to them and I wired them + +- - and tested ohms on the left + and right -

They do add, they increase by .3 ohms...


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## robbo266317 (Sep 22, 2008)

Are you measuring these with the crossover connected? 
If so then try just measuring the speakers, without the crossover, and a single wire joining the + to -


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## swong46 (Feb 15, 2010)

When I just do the mids or tweets, I get a higher "correct" reading.

Now what do I do about the two crossovers?


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## swong46 (Feb 15, 2010)

Can I wire both mids and tweets through one cross over? Will the cross be able to handle the power?


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## lsiberian (Mar 24, 2009)

swong46 said:


> Ok, well ohms law didnt really fail but I have a pair of car audio component speakers that are 4 ohm each.
> 
> I wired the crossover input wires in parallel and got a 2 ohm load. When I wire it in series, it is still 4 ohm, not 8 ohm...
> 
> Any help?


Wouldn't you only have one crossover input wire per output? 

I'm not a car audio guy, but the crossover simply distributes the correct frequency range to the speaker components. This is almost always done in parallel. But you only get a parallel load if you have dual drivers on one of the frequency ranges.


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## ryan750 (Aug 14, 2009)

swong46 said:


> So, can I just hook up the speakers to my receiver and play a certain sine frequency and then measure the ohms? or will that somehow mess up the receiver?


No, never do that, you'll probably bust your receiver or give it a very very hard time of it's life lddude:... 
Try using speaker workshop, it measure impedance using your sound card's line in/out and a ref resistor


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