measuring a cabinet's speaker resistance

  • Thread starter Thread starter neilli
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neilli

neilli

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Guys - I'm trying to check the wiring for my speaker cab and frankly I have no idea what I'm doing. I thought I could plug a cable in and set the multimeter to ohms and just get a reading but apparently not. I've checked continuity and that's good, so it's not like I'm plugging into a dead jack or whatever, but i have no idea how to check what the actual cabinet is wired to. If it matters, it's an old-school mesa 4x12, with one 8 ohm input and two 4 ohms (top and bottom).

Any help would be greatly appreciated!
 
What's happening on your multimeter? Any reading at all? What kind of cable are you using and how are you testing?

FYI don't expect a meter set to read ohms to read exactly 16 or 8 or 4 when measuring a speaker/cabinet. The ohm rating on the labelling is impedance, not resistance.\

16ohm cabs usually read around 13ohm on a meter that is measuring resistance. 8 ohm cabs read around 6 or 7 ohms.
 
I'm using a 'proper' speaker cable (i.e. not a guitar cord). I've set the meter to every one of the ohm readings and then put one terminal on the tip of the speaker cable jack, the other terminal on the sleeve of the jack. And I can't even get a steady reading - it's just reading all kinds of numbers and never settles LOL

Oh, and I should say at this point that each of the jacks works - I've tested each of them using my rack which has an old tubeworks mosvalve poweramp which doesn't care about speaker loads..
 
This is what the panel looks like on the inside:

DSC01930_zpsdad9oqbf.jpg


and this is the meter:

DSC01933_zps6dayhv63.jpg
 
I assume if you touch the two meter terminals to each other the meter reads 0?

Since you have access to the inside of the cabinet try measuring the different points on the connector in there instead of trying to keep meter terminals stable on a 1/4" jack.
 
Yeah. Or like 0.002.

I just tried the ground sleeve and live 'arm' of the cabinet socket (sorry, I'm not sure what the proper terms are) and it went to 0.07 then 0.08 which seemed positive for 8 ohm, but then went to like 16.00, .24 and so on. But the 0.07 and 0.08 kept coming back round..

EDIT: tried again and it was 0.06 and 0.07 pretty consistently. The socket is fairly old and not the tightest, but it's never cut out on me and I've used it a decent amount..
 
Looks like a cheap crappy meter. This may help:
Clean meter leads with scotchbright or fine sandpaper
Spray some contact cleaner, or put a SMALL dab of dielectric grease on the meter lead plugs (Thats where the lead plugs into the meter) Twist the plugs back and forth to clean any oxidation off the connection
Do not touch the meter leads, or speaker cable Tip/Sleave when taking readings
Spray contact cleaner on speaker cable tip/sleeve, insert into speaker jack and twist back and forth to clean jack contact points
Make sure your meter has fresh alkaline batteries

Oxidation and poor contact makes reading resistance virtually impossible... If you try all that and still get erratic readings go get a Fluke DMM...
 
neilli":hxmltig1 said:
This is what the panel looks like on the inside:

DSC01930_zpsdad9oqbf.jpg


and this is the meter:

DSC01933_zps6dayhv63.jpg
Click to expand...

I'm not familiar with that style jack with the 4 terminals (or atleast appears to be 4 terminals)

But 6.6ohms between the lead and ground on the main jack would point it to be 8ohms and wired correctly. Seems like a parallel-series wiring of four 8ohm speakers. The whites and balcks wired together on the top/bottom jacks take the 8ohm speakers and wire them in parallel to make 4 ohm output. Then that main jack seems to have the connections from the top/bot jacks in series to create 8ohm load (looks like the top jack white wire group is wired to the bottom jack black wire group, wiring them in series 4+4=8).

Are you sure the exposed metal wires on the main jack are not touching eachother ?
 
What everybody said already is correct. An 8 ohm cab will read 6.? when you measure it. This happens because the 8 ohm rating is measuring impedance, not resistance. I'm sure there's a wiki on impedance- look it up and give it a good read.
 
yep - a 16 ohm rated cab will measure more than 8 ohms and 16 or less, an 8 ohm cab will measure more than 4 ohms and less than 8 ohms and a 4 ohm cab will measure 4 ohms or less...
 
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