ohm loads

[rosrock 10+ year member]

how come my dual 2 ohm subs read 1.7 each on my dmm when parrallelled, and then when when theyre both parralleled together it reads they only go down .4 to 1.3? I thought if 1.7 was parrelled itll go down in half to ~.85. Im lost... help.

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[ahole-ic]

You're learning the difference between DC resistance and AC impedance. Enjoy.

 

[rosrock 10+ year member]

what? whats that mean? did i use the wrong dmm setting?

 

[ahole-ic]

what? whats that mean? did i use the wrong dmm setting?

No. your multimeter reads DC resistance. You don't have a way to measure AC impedance which is what subs are measured with.

 

[rosrock 10+ year member]

huh???? wth i bought i dmm off ebay... it has lots of settings, which one do i use?

 

[rosrock 10+ year member]

help pls?

 

[ahole-ic]

huh???? wth i bought i dmm off ebay... it has lots of settings, which one do i use?

I don't know what settings yours has. Usually it will be 20, 200, and 2000. You would want to be on the 20 setting. Then you touch the leads making sure your fingers are not touching metal (because this puts another path in parallel and slightly drops the reading) to each individual voice coil + and -. Write down the reading for both. If it jumps around a little that is normal.

Now, wire both + together and both - together. Take a reading from each of the joints you just made.

Now, you are reading DC resistance. This is not how your subs are rated. They are rated in AC impedance. What does this mean? It means that what you are testing for is not exactly what we are using. Why? Well for your speaker to reproduce music, it has alternating current or AC pass through it. The same resistor in an AC circuit will not have the same effect on the current in a DC circuit. For this reason we call resistance on DC "resistance" and resistance on AC "impedance". Impedance can be measured, but not with your little meter.

So, what did your measurements tell you? They told you that your voice coils were good. That's about it.

 

[rosrock 10+ year member]

dude, so are you saying theres no way for me to see what they read when i parrellel? if i cant do it with my dmm is there a place i can go to find out?

 

[Haunz 10+ year member]

your initial readings make no sense... you should be getting the .85 you are looking for with the coils in parallel...

It is common for a '2ohm coil' to read between 1.5 and 2.3 ohms DCR... generally they read below 2ohms, or I personally wouldn't consider it to be a 2ohm coil..

Don't forget to subtract the resistance of the dmm test leads...

 

[rosrock 10+ year member]

resistance of the dmm leads? what do u mean by that. each coil reads 2.7. then parrelled the sub reads 1.7 then when i hook both subs together parrelled i get 1.3. i have it on setting 200.

 

[rosrock 10+ year member]

im about to go try again

 

[smoka 10+ year member]

Impedance can be measured, but not with your little meter.

If my memory serves me correct, resistance is equal to impedance when the phase angle = 0. So I believe if you find a test tone at the correct resonant frequency, then you can use a normal ohm meter to measure impedance.