checking ohms on new cab

BassMan99 · #1 03-23-2011, 03:36 PM

I just received a GK 410MBE cab. Ordered on line. They mixed up the order and had it for a 4 ohm when I received the confirmation. I had asked for an 8 ohm. They said they caught it before it shipped and shipped an 8 ohm.

I received it today. The box had been retaped, obvious it has been opened. And the paper tag on the back of the cab that says its 8 ohms is only half stuck on. It looks like it may have been removed and reapplied. not very sticky

So I hate to be so suspicious but I checked the cab ohms with my multimeter. Using a speaker cable it reads 5.2
I know thats not the best way to read the ohms but I used a short cable, checked it multiple times.

Question is does that sounds like an 8 ohm or a 4 ohm cab based on that reading?
Thanks

greenboy · #2 03-23-2011, 03:37 PM

That's an 8-ohm cab then.

tjh · #3 03-23-2011, 03:44 PM

so to check this, you plugged a speaker cable into the jack on the cabinet, and then touched your probes to + and - on the other (exposed) end of the speaker cable? ... and then, why does a 5.2 reading translate into an 8 ohm cab?? ... cant pass up a learning opportunity here .. thank you

Rookwood · #4 03-23-2011, 03:50 PM

A multimeter is reading DC resistance vs. actual impedance of the speaker. DC resistance will read lower than AC impedance, but it's a good enough way to check the the speaker as multimeters are cheap and easy to obtain.

Quote:

Originally Posted by tjh

so to check this, you plugged a speaker cable into the jack on the cabinet, and then touched your probes to + and - on the other (exposed) end of the speaker cable? ... and then, why does a 5.2 reading translate into an 8 ohm cab?? ... cant pass up a learning opportunity here .. thank you

dincz · #5 03-23-2011, 03:52 PM

Quote:

Originally Posted by tjh

so to check this, you plugged a speaker cable into the jack on the cabinet, and then touched your probes to + and - on the other (exposed) end of the speaker cable? ... and then, why does a 5.2 reading translate into an 8 ohm cab?? ... cant pass up a learning opportunity here .. thank you

The meter doesn't read impedance - it reads the DC resistance, which doesn't include the voice coil inductance. Resistance of a speaker is usually approximately 3/4 of its rated impedance.

BassMan99 · #6 03-23-2011, 03:54 PM

tjh that is what i did. thanks everyone
it sounds good so far. I had an avatar b212 delta. about 6 years old 70 lbs is too heavy to carry myself. I am hoping this wil be loud enough and easier to carry myself.
Have two long gigs this weekend. That should start breaking it in!

Sneakypete · #7 03-23-2011, 03:54 PM

Impedance and resistance (which is what you measure with a multimeter) are different. Impedance varies with the frequency of the signal passing through the coil, lower impedance at lower frequencies IIRC. When you use a multimeter you simply pass a small DC voltage through the voice coil. In my experience the resistance always seems lower than you'd expect; 5 point something for an 8 ohm and 3 point something for a 4 ohm seems about average.

BassMan99 · #8 03-23-2011, 04:04 PM

good to know. Thank you all!

**IvanMike** · #9 03-23-2011, 04:29 PM

Quote:

Originally Posted by dincz

The meter doesn't read impedance - it reads the DC resistance, which doesn't include the voice coil inductance. Resistance of a speaker is usually approximately 3/4 of its rated impedance.

right-o. IIRC, there might be something in the FAQ regarding this and the nominal readings you might expect using a multimeter when testing cabs of various impedances. Not exactly intuitive, and this has freaked many an individual out!

BigOldHarry · #10 03-23-2011, 04:32 PM

Quote:

Originally Posted by BassMan99

tjh that is what i did. thanks everyone
it sounds good so far. I had an avatar b212 delta. about 6 years old 70 lbs is too heavy to carry myself. I am hoping this wil be loud enough and easier to carry myself.
Have two long gigs this weekend. That should start breaking it in!

You learn something every day.

I checked the impedance on an 8 ohm cab a while back and my meter said something much closer to 8ohms than 5... Maybe my meter is *really smart*?? (it *is* a Fluke...)

billfitzmaurice · #11 03-23-2011, 05:26 PM

Quote:

Originally Posted by IvanMike

right-o. IIRC, there might be something in the FAQ regarding this and the nominal readings you might expect using a multimeter when testing cabs of various impedances. Not exactly intuitive, and this has freaked many an individual out!

In theory DCR will read about 0.7 x impedance.

BigOldHarry · #12 03-23-2011, 05:32 PM

Quote:

Originally Posted by billfitzmaurice

In theory DCR will read about 0.7 x impedance.

So, using advanced calculus we can determine that 8 x0.7 = 5.6

about what he read on his meter...

!SCIENCE!

BassMan99 · #13 03-23-2011, 06:10 PM

i think it sounds very good so far. very small for a 4x10. i think it is a just a paper tag for the model/ohm label and it must of just come loose.
you guys have made me feel confident its 8 ohms. Important if I use it with a 2nd cab for a big show. although best i can tell now i may never need to do that. its loud.

gmarcus · #14 03-23-2011, 08:03 PM

What does it sound like? Can you compare it to any other cabinets?

Thanks

tjh · #15 03-23-2011, 08:20 PM

Outstanding information ... I felt kind of dumb asking for an explanation of the process and why, but I am far too old to not ask a question if I feel the need to ... thanks to all for taking the time to explain so well ...