Checking cab impedance with a meter?

[DrNewcenstein]

I have a Mesa halfback 4x12 with Peavey Sheffield 1290s in it (used, obviously), and they are attached to (I'm assuming) the original Peavey MS1290 cab's impedance switching jack panel. Because it's been modded by a non-professional, I don't trust what the jack panel says regarding impedance.

Is it possible to plug a speaker cable into the cab and stick a multimeter on the other end of the speaker cable and tell whether it's wired for 16, 8, or 4 Ohms? Tracing the wires to their terminals will only get me so far since they're braided/twisted together, and all 4 speakers use one blue and one yellow, rather than multiple colors for easier tracking.


I've had the cab for about 3 years now and have never used it because I'm unsure of the actual impedance. I suppose I could just rewire the damn thing
Didn't think of that til just now.

[Securb]

Re: Checking cab impedance with a meter?

Yep you can check it with a meter. I asked this question myself just a few months back.

[PFDarkside]

Re: Checking cab impedance with a meter?

Yes. Due to the difference between impedance and DC resistance, your meter will read approximately 20 - 25% lower than the actual impedance.

~13ohms DCR = 16ohms
~6.5ohms DCR = 8ohms
~3.2ohms DCR = 4ohms

[IM4Tone]

Re: Checking cab impedance with a meter?

Yes. Due to the difference between impedance and DC resistance, your meter will read approximately 20 - 25% lower than the actual impedance.

~13ohms DCR = 16ohms
~6.5ohms DCR = 8ohms
~3.2ohms DCR = 4ohms

Exactly correct! It's a multiple choice answer....for example, don't worry if the reading is 5.9 or 6.8 ohms. That's nominally an 8 ohm speaker, and not a 16 nor a 4.

[King IzzO)))]

Re: Checking cab impedance with a meter?

Speakers generally meter lower than labeled. 8 ohm speakers will read 5~6 ohms, etc. Just find a diagram double check it.

[DrNewcenstein]

Re: Checking cab impedance with a meter?

Thanks all

King: The sheet that came with my Carvin 2x12 does include various 4x12 diagrams (series, parallel, 4, 8, 16 Ohm) but with the way the wires are twisted together and braided, it's hard to follow the path of all the wires to make sure they're going according to a given diagram. As well, there are these little plug connectors where they go into the panel, which I've never seen before (I'm used to push-on connectors like are on the speakers going straight to the jack - these go to a switch), so I don't know if those might be inverted somehow and what the results may be (i.e. wired for 16 Ohms at the speaker terminals but reversing the plugs cuts it down to 8 Ohm, etc).

Typical hazard of used gear: no idea who's been screwing around with it and whether it's right. They got rid of it for one reason or another, after all.


Maybe I'll just rewire it anyway to be safe

Thanks again

[zzmoore]

Re: Checking cab impedance with a meter?

Are you saying there is a Peavey Switch/Connector Panel on the Mesa cab.?

[Myaccount876]

Re: Checking cab impedance with a meter?

Usually the speakers will come in at about 2 ohms of difference when measuring in DC. Because the impedance rating is AC. I also notice when measuring 4 speakers wired in whatever, the reading is more off because of the amount of play in reading increases with every speaker you add on. I'd measure each speaker individually, write it down, and wire it and do the math to find the final impedance rating.

[DrNewcenstein]

Re: Checking cab impedance with a meter?

Are you saying there is a Peavey Switch/Connector Panel on the Mesa cab.?

Yup. Genius previous owner bolted the panel onto the rear of the cab.

Is the twisting of the wires crucial, or just for neatness? If I'm going to rewire it, I'll just run them straight from point to point unless there's some mystical reason for the twists.

And yeah, 3 months later and I still haven't touched it

[PFDarkside]

Re: Checking cab impedance with a meter?

Twisted pair is done for noise rejection. You probably won't notice too much of a difference with speaker level voltages.

[ehdwuld]

Re: Checking cab impedance with a meter?

I twist wires in cabinets to make nice neat cabling

*(Sent from my durned phone!)*