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Testing resistance in a cabinet.

creis2

creis2

Guest
Nov 11, 2011
703
1
Cambridge, MA
#1
So I have an older model nv610. I know the newer model's drivers say 24 ohms and are wired in series, for 4 ohms. My drivers say 32 ohms, which should end up being 5.3333 ohms for my cab. The back of my cab says 4 ohms however.

I emailed bergantino a few weeks ago, no response.

I just wanted to give it a simple ohmmeter test, but after searching the forum, I'm thinking it might not be that simple. On a similar thread I found this:

"You didn't use an ohmmeter to measure the ohms, did you? What were you thinking????

Seriously, the ohmmeters on regular multimeters measure DC resistance (in ohms), not AC impedance (in ohms). Apples and oranges.

Speakers are coils of wire (inductors), so their resistance is very low to DC, totally different to AC. Add interactions with the air in the cab restricting cone motion, affecting back EMF generated by the mag structure, and the AC impedance ends up a weird curve based on frequency, not like an inductor at all."

Not sure what this means, but can I get an honest number from putting my ohmmeter on the speakers?
 
#4
skychief said:
You can use an ohmmeter to check the impedance of your driver. :)

The ohm reading will read somewhat lower than the impedance of the driver.

A 4 ohm driver will read about 2.6 ohms

an 8 ohm driver, about 5 ohms

a 16 ohm driver, 11 or 12 ohms,,,etc...
Click to expand...

you cannot use a standard multimeter to measure impedance. What you are measuring in the DC resistance of the voice coils.
 
#5
You are correct when you say that you may not get proper readings when you check the speakers with an ohm meter. Impedance (speakers) is different than resistance, so you will only get a very rough idea, if at all by using an ohm meter.

Actually, if your cabinet is a 610 (six ten-inch drivers), then your impedance for that cabinet using 24 ohm speakers should be 4 ohms, if my math is correct. Using 32 ohm speakers, the result should be, as you've calculated, 5.33333 ohms. Note, though that the speakers are wired in parallel, not series. To do so would result in an impedance of 144 ohms for the cabinet with 24 ohm speakers and 192 ohms for the 32 ohm speakers.
 
#6
Impedance is more complicated than resistance - it takes into effect everything that is happening when the driver is actually being driven by audio, which is what matters to an amp.

The resistance measurement can be taken only as a rough guide, such as determining that the cab is 4 or 8 ohms, etc. And Bassman is right - they are in parallel.
 
#8
Above +1. Impedance has a reactivity element to the computations that go beyond simple DC resistance.

So the fact that you're getting a DC resistance reading in the ball park of the nominal impedance tells me your speaker cabinet is just fine. Rock on!
 

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