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Acid Test
12-27-2010, 04:41 PM
I am trying to measure the impedance of a 2x12" cabinet wired in series with 2, 8-ohm speakers. Using a Fluke voltmeter, I am getting 26 ohms.

I had thought that this type of measurement would yield a result that is somewhat less than the expected 16 ohms and not more. Any suggestions?

Using the same voltmeter on an 8 ohm 4x12 give 6.4 ohms and on a single 1x12 with an 8 ohm speaker I get 5.8 ohms. All measurements are taken without any signal using a plug in the speaker jack.

GuitslingerTim
12-27-2010, 05:02 PM
I am trying to measure the impedance of a 2x12" cabinet wired in series with 2, 8-ohm speakers. Using a Fluke voltmeter, I am getting 26 ohms.

I had thought that this type of measurement would yield a result that is somewhat less than the expected 16 ohms and not more. Any suggestions?

Using the same voltmeter on an 8 ohm 4x12 give 6.4 ohms and on a single 1x12 with an 8 ohm speaker I get 5.8 ohms. All measurements are taken without any signal using a plug in the speaker jack.

The correct term is multimeter, or ohmmeter, not voltmeter, which is used for measuring volts.

If the readings are correct, the two speakers are 16 ohms, wired in series.

ReginaldBisquet
12-27-2010, 05:04 PM
Test each speaker separately (and unplugged) with the voltmeter. Perhaps one of the speakers has a broken connection that's making the reading go nuts.

Otherwise, bring it over and I'll take good care of it. :)

Acid Test
12-27-2010, 05:15 PM
The correct term is multimeter, or ohmmeter, not voltmeter, which is used for measuring volts.

If the readings are correct, the two speakers are 16 ohms, wired in series.

Problem is the speakers are each 8 ohms - It is the only impedance Eminence made the Lynch Super Vs in.

I have two of these 2x12 cabs which are identical in wiring but have different sets of 8 ohm speakers

Cab 1: Two Eminence Man-O-War speakers, 8 ohms each. Measurement 26.2 ohms

Cab 2: Two Eminence Lynch Super vs, 8 ohms each. Measurement 26.0 ohms

Connect the cabs using the parallel in/out yields 9.6 ohms

Acid Test
12-27-2010, 05:17 PM
Test each speaker separately (and unplugged) with the voltmeter. Perhaps one of the speakers has a broken connection that's making the reading go nuts.

Otherwise, bring it over and I'll take good care of it. :)


Was hoping to get an answer without having to take them apart. The Redstar cabs have several screws holding the front metal grill to the cab. Each has a rubber spacer you have to line up. Cabs are front mounted but maybe there is a way to get individual measurements opening the back jack plate.

ReginaldBisquet
12-27-2010, 05:27 PM
Then you might have the meter on the wrong setting or the testers plugged into the wrong input. Test the meter on a spare speaker to see if the measurements are close to the speaker rating.

tone4days
12-27-2010, 05:47 PM
make sure you are measuring AC impedance .. not DC resistance

Blue Strat
12-27-2010, 05:53 PM
make sure you are measuring AC impedance .. not DC resistance

You can't do that with a multimeter.

There's no way that either
1) Your meter's battery is good or
2) those are both 8 ohm speakers or
3) that your measuring what you think you're measuring (or that your probes are in the right holes in the meter)

An 8 ohm speaker will measure approximately 6 ohms when using a digital multimeter because it's measuring DC resistance, NOT impedance.

Start with a new battery and try again. If you're not getting around 12 ohms for the series pair, they're not both 8 ohm speakers. Disconnect them and measure each speaker, one at a time.

VaughnC
12-27-2010, 06:43 PM
Something sounds fishy.

What does your meter read with both probes touching each other? 0.0 ohms? Check a 10 ohm resistor with the meter.

tone4days
12-28-2010, 07:44 AM
You can't do that with a multimeter.
perhaps not with some multimeters ... but my fluke can do this ... of course it is an approximation because impedance is a function of frequency ... but it is surely close enough for my purposes

SatelliteAmps
12-28-2010, 10:17 AM
perhaps not with some multimeters ... but my fluke can do this ... of course it is an approximation because impedance is a function of frequency ... but it is surely close enough for my purposes

Which Fluke model is that? Most can measure frequency, but not DC impedance. Haven't heard of one having a DC impedance setting.


As for the OP, having two incorrectly wired cabinets is the most likely cause here. If you are measuring other things correctly, as you've already stated, then measuring these cab's and having it come up like this means something isn't wired right. Putting two cab's that measure 26.2Ω each in parallel shouldn't get you 9.6Ω, it should get you 13.1Ω. So, that means something is wrong (or the other possibility is that you have either a crossover or a horn involved that is changing what you are expecting to see.)

Acid Test
12-28-2010, 10:30 AM
I am almost too embarrassed to say the problem was a low battery. Changed it and all is fine.

Sorry to bother you guys with this but I do greatly appreciate the responses and learned a lot about these measurements.

kevinhifi
12-28-2010, 10:35 AM
You shouldn't be embarrassed at all. We've all pulled out our hair to discover that the battery is dead, the strings are old, the polarity is reversed, the power is off, or many other really simple things.

That's what the forum is good for. Glad you got it figured out. My multimeter lets you know when the batter is running low. Maybe yours does too?

tone4days
12-28-2010, 11:13 AM
Which Fluke model is that?
8060A ...
http://www.teknetelectronics.com/Pics/WEBFLUKE8060A.jpg
please don't laugh - it's frikkin' ancient (20+ yrs old) ... i wish it would die so i could replace it with a modern one (auto-ranging, etc) ... it has been absolutely bulletproof

Blue Strat
12-28-2010, 11:42 AM
I am almost too embarrassed to say the problem was a low battery. Changed it and all is fine.

Sorry to bother you guys with this but I do greatly appreciate the responses and learned a lot about these measurements.


It's the last thing we suspect. Once it's happened one time it moves up on the list.

Blue Strat
12-28-2010, 11:43 AM
8060A ...
http://www.teknetelectronics.com/Pics/WEBFLUKE8060A.jpg
please don't laugh - it's frikkin' ancient (20+ yrs old) ... i wish it would die so i could replace it with a modern one (auto-ranging, etc) ... it has been absolutely bulletproof


I've got one of those too. Never noticed an AC impedance function but never really thought to look either.

amphog
12-28-2010, 02:05 PM
My 8060 does not measure impedance.

tone4days
12-28-2010, 10:00 PM
is it not impedance to push the 'AC/DC' button in (for AC) and measure ohms?

VaughnC
12-29-2010, 12:24 AM
is it not impedance to push the 'AC/DC' button in (for AC) and measure ohms?
Impedance is only true for one frequency so, in order to measure impedance, a meter would also need a test frequency selection.

tone4days
12-29-2010, 07:44 PM
Impedance is only true for one frequency so, in order to measure impedance, a meter would also need a test frequency selection.
yes, of course - just like i mentioned in #10 above <eyeroll> ... but for practical purposes, i have never heard any musician specify a frequency when stating an impedance for a speaker - the average over the useful range is good enough, no? ... lets not be impractically pedantic

MRscratch
12-29-2010, 07:59 PM
i dont know why this is a problem!
on a digital multimeter. take your speaker lead, take the meter and put it on ohms. use a lower range. ie , mine has a 200ohm range.
then measure across the tip and sleeve.
a single celestion 8 ohm comes in around 6.8- 7 ohms
a 16 ohm comes in around 15.6 ish.
a 4/12 with 16 ohm load, will register 15.6
this is the total ohms you can measure.
i beleive that the impedance is the the vector sum of A squared(watts) plus B squared ( rl+- xl) square rooted !
so C squared equals A squared + B squared square rooted.
that is the impedance. you cant measure that. i dont believe that inductance and reactance of the speaker is not usually know to the user.
or am i just full of $#it? :D

VaughnC
12-29-2010, 10:33 PM
yes, of course - just like i mentioned in #10 above <eyeroll> ... but for practical purposes, i have never heard any musician specify a frequency when stating an impedance for a speaker - the average over the useful range is good enough, no? ... lets not be impractically pedantic
Understood...but back in the day, they taught us in electronics school that speaker manufacturers usually quoted speaker impedance at a frequency of 100 hz.. However, a multi-meter manufacturer wouldn't know that you are testing a speaker so, having an impedance scale wouldn't mean much without knowing your intended purpose. Just sayin'...as most people don't know the difference between impedance and resistance and are confused because both are measured in "ohms". To avoid the confusion, I've often wished that they had originally given impedance & resistance measurement units different names...but it is what it is ;).