What Ohm is my cab?

Quattroste

The cab is a Mongotone 2x10 with Jensen P10r's in it. When I bought the cab i was told it was 8ohm. I had it working using the 8ohm output from my amp but then it stopped working. Anyway I'm trying to fix this issue so I opened it up to test the wiring(which is fine) but I noticed the 2 Jensens are 16ohm.

The wiring is basically 2 red and 2 black wires coming straight from the input jack and one of each wire going to the speakers. Does this half the ohm value?
The two speakers are not connected together in any way.

Also which colour wire is usually + and which is – ?

Gaspode

Where's Eoin Madsen when you need 'im!

feylya

Red is + and black is - usually. Sounds like your cab is wired in parallel so the formula is 1/Rt = 1/R1 + 1/R2 so that's bring your cab to 8ohms if your 2 speakers are 16ohms each

Voodu Child

Yep, what he said^
The speakers are in parallel, so its 8ohm overall.

Quattroste

Thanks lads. All the wiring is fine.

How can you tell if a speaker is blown? I never had it loud enough to blow but I am getting nothing from the speakers. This is p*ssing me off now. I tried connecting the wires from the stereo speakers to test but nothing! :mad:

DeadSkin

Do ya have a multimeter handy?

Quattroste

Nope! No multimeter.

Paolo_M

Best way to test for a blown speaker is to

• Turn of your amp
• Grab a 9V battery
• Disconnect the speaker cable from the amp output
• Connect the battery across the tip and sleeve of your speaker cable
• If the speaker is ok it will produce an audible pop noise
• You can also use this to check that the wiring is correct. The speaker cones should all move in the same direction otherwise you have a speaker wired out of phase

Eoin Madsen

Nice bullet pointing! :pac:

Quattroste, did you figure out the problem with your speakers?

Quattroste

I still have to do the nicely bullet pointed test that Paulo mentions. I'll do that tonight and report back.

Tha speakers are rated at 25 watt and the amp is 7 watt and was never loud as I was basically only testing it in my house for a couple of hours. It was working fine. I moved the amp and cab when rearranging furniture and then the cab no longer worked after that. I cannot understand how the speakers would be blown (if they are).

Eoin Madsen

It's often easier to blow higher rated speakers. If the speakers aren't getting enough energy to push past their basic mass/momementum, they won't move much air. When the speaker level is low, it's easier to crank up the amp past clipping without realising it. Clipping creates square waves, and square waves make speakers die.

In saying that, what you describe does sound strange. The fact that it happened after moving the amp is probably not coincidental. I'd move them back. :pac:

Paolo_M

Quattroste wrote: »

I still have to do the nicely bullet pointed test that Paulo mentions. I'll do that tonight and report back.

Tha speakers are rated at 25 watt and the amp is 7 watt and was never loud as I was basically only testing it in my house for a couple of hours. It was working fine. I moved the amp and cab when rearranging furniture and then the cab no longer worked after that. I cannot understand how the speakers would be blown (if they are).

Hey, I hope I didn't do all the bullet pointing for nothing!! :pac:
What's the story, are your speakers ok?

Quattroste

Paola. Your bulleting was not in vein. I didn't get to it last night as I am up to my bollix in work and was only ready to sleep when i got home. Back to the same crap today but I'll give it a go tonight if I'm not too late again. :mad:

Quattroste

Right I just did the battery test and no pop, not even a crackle or snap :pac: nothing.

New speakers required I guess. I'm thinking Greenbacks.

feylya

If you can get a loan of a multimeter, check all the resitences across the speakers and the wires. Sounds strange that both speakers are blown.

Quattroste

I know all the wirings work as I took the jackplate unit and tested that none of the circuits were broken. Does anyone have a spare 10" speaker I can borrow?