Troubleshooting Subwoofer

SSTJ

SSTJ

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Any audiophiles out there?

I have an 8" Rockford Fosgate subwoofer that isn't giving me any output. The speaker cone still moves up and down freely when I press on it. But when I connect a multimeter to the + and - terminals, and set the multimeter to "Ohms" (resistance), I get "Overload". I've read that if I get NO resistance, there may be a problem with the coil. But what about when I get infinite resistance, as in "Overload".

To add to the mystery, it doesn't always read "OL". Sometimes it reads something very high, like 4M (i.e. 4,000).
 
I don't know what overload means, you probably are pushing on the cone with the meter hooked up and generating voltage that is freaking your meter out. Measure the resistance without touching the cone. It should be steady. Change the meter to voltage and very gently push the cone, it should read positive and negative voltage. You can also tap the terminals with the meter set to resistance, the speaker should click as you touch both terminals.
 
Thanks. "Overload" is when the multimeter can't push any current through the circuit because either the circuit is open, or else because the resistance is just too strong.

And no, I'm being careful to set the sub upright and level, with nothing pushing on the cone when I test the Ohms. If I do push on the cone, up and down, while the multimeter is connected, the Ohms go up and down like crazy.

Ok, I can try setting the multimeter to V (direct, I assume) and push the cone. Will see what happens.
 
Yea, that's what I've heard. Just wanted to ask around, because everything I've read says that when a coil is damaged the multimeter will read "0" resistance, but I'm getting "OL", which suggests maybe a different problem. I'd like to repair it if possible, but I'm learning as I go.
 
SSTJ said:
Yea, that's what I've heard. Just wanted to ask around, because everything I've read says that when a coil is damaged the multimeter will read "0" resistance, but I'm getting "OL", which suggests maybe a different problem. I'd like to repair it if possible, but I'm learning as I go.
Click to expand...
The voice coil can short which would lead to a low resistance similar to connecting the probes on the meter together. The voice coil can also break or burn out or the wires connecting to it can break which would read on the meter just like not touching the probes together or open circuit.

Does the speaker move smoothly when you gently press on the center with no grinding or rough feeling at all? Does it tick when you connect the meter to the terminals to read resistance.

There are very few repairs you can do to a speaker unless you are pretty experienced.
 
Thanks again. When I move the speaker cone with my hand, I do get a little bit of grind at the lowest point. And yes, if I move it up and down while the multimeter is connected and set to mV, I get about 100mV at most.

No, when I connect the multimeter set to Ohms/Resistance, I get no tick from the speaker at all.

Sounds like maybe the coil is broken or burnt or something?
 
SSTJ said:
Thanks again. When I move the speaker cone with my hand, I do get a little bit of grind at the lowest point. And yes, if I move it up and down while the multimeter is connected and set to mV, I get about 100mV at most.

No, when I connect the multimeter set to Ohms/Resistance, I get no tick from the speaker at all.

Sounds like maybe the coil is broken or burnt or something?
Click to expand...
Ya, that's a pretty common thing but if you are getting voltage when you move the cone it might still just be the wires connecting to the coil. Sometimes they crack right at the joint where the terminals connect or at the blob of glue on the back of the cone where they enter. It is possible to resolder those connections carefully and patch any holes with epoxy or hot glue at the cone but you are pretty likely to break the speaker at that point - might be worth trying before the trash.
 
Ok, thanks. So far, I have removed the outer edge of the cone from the metal base. But the speaker cone is still connected to the coil, and that is still connected to the magnet. How do I remove the magnet? Just pry it off, or does it twist off? I can upload a pic later perhaps.
 
I think if you remove the cone you have to replace the lower support with a new one when it goes back in. That type of disassembly is well above and beyond my personal experience. Good luck with it.
 
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