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How can I tell if my woofer is blown?

Moth R. Superior

Moth R. Superior

Active Member
This seems like an obvious question, I know. However, I've not ran into this before.
I recently purchased a pair of Fisher XP55b's (I know they're not exactly the "Cadillac" of loudspeakers), because A, they were practically free, and B, they match the set of XP44's that my wife loves. (she just really likes the appearance, the grills and all).
Typically I've found that the XP's of this vintage are pretty decent sounding speakers, after a recap, and all 4 are practically "showroom" new looking.
So I hooked them up and one of them sounds even better than I expected, which makes 'em keepers for a time anyway, the other, not so much.
At first the low end was somewhat present, but with an extremely ugly sounding 'rattling.' After about a minute and a half the bass fell out all together. Before that happened, it had a lot of, well, I guess I'd describe it as "static". I removed the grills, and was expecting to see little to no foam surrounding the cone, however the foam was completely intact, even near perfect looking.
I guess what I'm asking is how do I diagnose exactly what's wrong with it?
I'd like to keep them and pair them with the others for out little bedroom set up, but I'm not gonna invest too much into them.
Any help would be greatly appreciated. I am still a student in the restoration department, and I like working on things, I just don't know where to start...
 
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I would start by gently pressing in on the cone and see if you can feel the voice coil rubbing. Since the foams look to be in great shape, they must have been replaced at some point. The voice coil may have not gotten centered and is rubbing the pole piece.
 
Hello Moth. I've never agreed with the whole "push the cone in" method. I've owned some extremely closely gapped JBL that were perfectly aligned, but you couldn't precisely hand push the cone without feeling rub.

Second, pull the woofer out of the cabinet, disconnect all wiring to the woofer, and measure it with a VM (ohms).
 
Thanks a lot everyone! I'm going to try all of these suggestions, and one way or another I'll get to the bottom of it! Just hope they're salvageable.
 
Pull the woofer out & drive it directly from the amp in mono. That should confirm that you have blown the driver. If you can get your hands on a signal generator so much the better. There's nothing complicated in this. A noob should be able to do this. Report back.
 
Lesterbest said:
If you can get your hands on a signal generator so much the better.
Click to expand...

There are many phone apps and computer downloadable signal/tone generators available for free. Easy to get, but first step is to use a DMM to see if the VC is open. If nothing else, just grab a AA battery and touch the leads with that and see if you get movement or an audible "thump".
 
Lesterbest said:
Pull the woofer out & drive it directly from the amp in mono. That should confirm that you have blown the driver. If you can get your hands on a signal generator so much the better. There's nothing complicated in this. A noob should be able to do this. Report back.
Click to expand...
Great advice.
 
I don't know if I am supposed to do this but, I usually tap the woofer and if it doesn't sound normal [you can tell the difference] there is a high chance it could be blown. That's also how I test for how well it might give off bass, if I can't connect it to an amp or receiver at that time, such as at a store.
 
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