Measured Re values

[Alex JB 10+ year member]

I have a SVC 4ohm sub, I know that the '4ohm' is a nominal impedance value and not the resistance over the coil.

I looked up the spec and it states a true resistance value Re of 2.6 ohm

With my multi meter I measure 2.9 ohm

I read that such low resistance values are difficult to measure correctly and the meter leads often add to the reading.

Does the value sound realistic?

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[garychoffmann 10+ year member]

Yes. Touch your dmm probes together and see what their resitance is. If touching the probes together yields .3 resistance you know your sub is actually sitting at 2.6 ohms. Slight variance is ok and to be slightly expected.

 

[Alex JB 10+ year member]

Tried with my meter and get 0.3 over the meter leads and 3.0 over the terminals, 2.9 over the leads.

It is frustrating as I thought this was right and a fella came to buy it and put a cheap pocket meter over the terminals, read 2.9 and said 'this is f$&@d mate, should be 4ohm'

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[JohnKuthe]

Yes. Touch your dmm probes together and see what their resitance is. If touching the probes together yields .3 resistance you know your sub is actually sitting at 2.6 ohms. Slight variance is ok and to be slightly expected.

Yep! My father has an old VOM in a little wooden suitcase thing. I used to like to set it at the correct Ohm setting and then squeeze the leads really hard to make my electrical connection a little better and watvch the needle deflect and try to drop my resistance as low as possible! Talk about an object lesson for the aspiring mad scientist electrical guy!

John Kuthe...

 

[NSTALN 10+ year member]

Tried with my meter and get 0.3 over the meter leads and 3.0 over the terminals, 2.9 over the leads.
It is frustrating as I thought this was right and a fella came to buy it and put a cheap pocket meter over the terminals, read 2.9 and said 'this is f$&@d mate, should be 4ohm'

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Your coil is fine…4ohm impedance is different from measured DCR across the coil. Many '4ohm nominal impedance' subwoofer coils measure about 3ohms of direct current resistance. Your mate is f$&@d up.

 

[JohnKuthe]

Your coil is fine…4ohm impedance is different from measured DCR across the coil. Many '4ohm nominal impedance' subwoofer coils measure about 3ohms of direct current resistance. Your mate is f$&@d up.

True, because you can think of impedance as the DC resistance you measure and the AC increased resistance over that with all the AC effects! A strict DC impedance is equal to it's measured DC resistance, but anything AC like a music signal has an additional AC produced "resistance" so we call the total "impedance".

John Kuthe...