#1
I recently got an empty 5150 cab to go with my 5150 II head, I put 4 Sheffield 1290 16 ohm speakers in it, and my multimeter isnt only reading between 12.5 to 13.4 ohms. Is this normal, Do I have a problem? I've never had to do this before so any help would be great.
#2
Why did you put a multimeter to it after you put 4 brand new speakers in it? If you wired it up the same way, it should work fine. You prolly aren't making a good connection with your multimeter, it's common to get a few ohms short if you don't make good contact.
#3
Why use a multi-meter??? It never hurts to double check. Measure twice cut once kind of a thing. We're talking about potentially screwing up an amp here. But yes, check to make sure you're making contact when you check impedance. Double check your wiring too.
#4
Im not 100%.. but arent speakers measured in impedance and not resistance? if they are then the impedance has a resistance part and an impedance part from the inductor (coil loop). The rest of the missing ohms are from the coil being an inductor in AC current
#5
It's a speaker, it's not like everything is gonna blow up if it's 3 ohms off, which you can't really do wiring up 4 speakers unless one is blown. You can get 4, 8, and 16 ohms out of any kind of wiring, series, parallel, and series parallel, you can't get 13 ohms, unless, something is blown, or you are missing part of your load.

EDIT: ^ That may be true.
#6
Quote by Initium
I recently got an empty 5150 cab to go with my 5150 II head, I put 4 Sheffield 1290 16 ohm speakers in it, and my multimeter isnt only reading between 12.5 to 13.4 ohms. Is this normal, Do I have a problem? I've never had to do this before so any help would be great.



Does your multimeter measure impedance?

If not, all it's done is measure the straight up DC resistance of the coil windings.

That's not the same as the audio frequency impedance.
#7
Loudspeaker, "impedance" is not just the measurement of its DC resistance. The voice coil contributes an inductive load as well as its pure DC resistance. So, you can't measure impedance with a simple ohm meter. The voice coil's pure DC resistance will always be less than the total reactive load. Considered in this way, 12 or 13 ohms sounds about right for a 16 ohm cabinet.

A speaker's impedance changes with frequency, dropping at the cone's resonant point.

In the end, the number attached as "impedance", (DC resistance + inductive load), really only represents an average anyway.

Quote by ethan_hanus
It's a speaker, it's not like everything is gonna blow up if it's 3 ohms off, which you can't really do wiring up 4 speakers unless one is blown. You can get 4, 8, and 16 ohms out of any kind of wiring, series, parallel, and series parallel, you can't get 13 ohms, unless, something is blown, or you are missing part of your load.

EDIT: ^ That may be true.
It's not!

Even assuming it was, a simple individual check of each driver separately, would find the culprit. The bad coil would either read open, (infinite resistance), or lower resistance than the others due to the insulation being burned off the windings, causing them to short together.
Last edited by Captaincranky at Sep 24, 2011,
#8
Quote by ethan_hanus
It's a speaker, it's not like everything is gonna blow up if it's 3 ohms off, which you can't really do wiring up 4 speakers unless one is blown. You can get 4, 8, and 16 ohms out of any kind of wiring, series, parallel, and series parallel, you can't get 13 ohms, unless, something is blown, or you are missing part of your load.

EDIT: ^ That may be true.


Don't be talkin if you don't know what your talking about.
http://en.wikipedia.org/wiki/Electrical_impedance
There's an article on impedance. It's way more complicated than simple DC resistance. That said, measuring DC resistance gets you close to the impedance rating and I'd say 13ohms DC resistance is probably the correct 16 ohms impedance.
#9
Quote by LeviMan_2001
Don't be talkin if you don't know what your talking about.
http://en.wikipedia.org/wiki/Electrical_impedance
There's an article on impedance. It's way more complicated than simple DC resistance. That said, measuring DC resistance gets you close to the impedance rating and I'd say 13ohms DC resistance is probably the correct 16 ohms impedance.


Read my edit.
#11
Quote by ethan_hanus
Why did you put a multimeter to it after you put 4 brand new speakers in it? If you wired it up the same way, it should work fine. You prolly aren't making a good connection with your multimeter, it's common to get a few ohms short if you don't make good contact.
Ethan, I don't know how you arrived at this conclusion. A "bad connection" would actually read as higher resistance, not lower.

Usually, you would do a rough check of an ohm meter's calibration by shorting the leads together. In this case, you should get a reading of zero. (No resistance).
#12
Quote by Initium
I recently got an empty 5150 cab to go with my 5150 II head, I put 4 Sheffield 1290 16 ohm speakers in it, and my multimeter isnt only reading between 12.5 to 13.4 ohms. Is this normal, Do I have a problem? I've never had to do this before so any help would be great.



Haven't read the whole thread so you might have heard this already but what you are experiencing in normal. Speakers are rated for alternating current and your multi meter runs direct current. This usually means that if you are checking the speakers with a multi meter they will read low. It's normal and not something to worry about.
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#13
Well like I said, I never had to fiddle around with anything like this before, and just got the amp so I don't want to **** anything up. So thank you to those who were helpful. Also, does it matter what output jack on the amp I plug the cab into?
#14
yeah it does, you have to match impedance of the cab (which ever way you wired it) to the impedance of the output (usually one to all three of these: 4, 8, 16 ohms)
Last edited by michaelbot9000 at Sep 25, 2011,
#15
A 13 ohm reading is about right. You've got nothing to worry about.

With a meter, you're only measuring 1 part of impedance, the real part, resistance. There's a complex component that your meter can't show you.
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#16
Quote by michaelbot9000
yeah it does, you have to match impedance of the cab (which ever way you wired it) to the impedance of the output (usually one to all three of these: 4, 8, 16 ohms)



It's a 5150, The outputs are left and right, It has an impedence selector switch. The cab itself only has one input jack on the back.
#17
the left and right is so you can run two cabs (full stack) so if you have only one you can choose either (just confirmed this with the 5150 manual online, the two outputs are in parallel).

You have to match the impedance of the whole cab to the output. If you changed the speakers to exactly the same impedance and exactly the same wiring, leave the switch where it was before. Otherwise, get your multi meter and look at the jack on the speaker. Measure the resistance between the tip and sleeve and pick which ever impedance is closest (remembering that the value you have on your multi meter will be lower than the actual impedance but close to it).

This is how i would do it, some one tell me if i am wrong
Last edited by michaelbot9000 at Sep 25, 2011,
#19
Quote by michaelbot9000
the left and right is so you can run two cabs (full stack) so if you have only one you can choose either (just confirmed this with the 5150 manual online, the two outputs are in parallel).

You have to match the impedance of the whole cab to the output. If you changed the speakers to exactly the same impedance and exactly the same wiring, leave the switch where it was before. Otherwise, get your multi meter and look at the jack on the speaker. Measure the resistance between the tip and sleeve and pick which ever impedance is closest (remembering that the value you have on your multi meter will be lower than the actual impedance but close to it).

This is how i would do it, some one tell me if i am wrong


I did all that, I just wanted to be safe and ask around. The cabs wiring wasn't confused me, it was the reading itself. But again, thanks to those who gave clear answers.