Need help with a speaker problem.

[srvprodigy]

I'm looking for any suggestions on a speaker problem I have. I have an 18" sub-woofer that keeps cutting out on me. I have checked the crossover by using an identical speaker with it and both work perfectly. I tested the ohms on the speaker in question and it reads normal (3.9 ohm). The cone moves just fine by hand (definitely not in DC) and the tensel wires look fine at the solder joints and where they meet the paper.
I need help from this point. What should I check next?
What the speaker does is sit quietly for a while, then suddenly blast out a quick burst of sound only to cut back out again.

Enzo.... You out there buddy?? I owe you a beer or two already for the help you've already given me on other projects. Much appreciations to you my friend. Thanks.

[Twist]

I've seen many speakers that behave like you described. It's typically where the two braided wires are attached to the voice coil and unfortunately it's under the center dust cap buried with epoxy. I have in the past cut the dust cover off and located the bad connection and managed to resolder it but it's not really worth the effort. Some speakers are crimped at that point.

[trevorus]

Run it outside the box with a test tone. See if it cuts out. See if you can replicate the cutting out, and then fiddle with stuff until it comes back.

[bbartilson]

What the speaker does is sit quietly for a while, then suddenly blast out a quick burst of sound only to cut back out again.

Enzo.... You out there buddy??

Second questions first - he's probably not. Saturday night is usually his only night off... hanging out with the wife and what not.

As for your speaker:

There are two likely scenarios:

1. The cone moves, but does it make any kind of scraping noise? Long term overpowering (or, too little power with too much distortion) causes the voice coil and former to get hot, and the varnish they finish those components with melts and gets all gooey. It then physically sticks the driver in place, and high power peaks will break it loose momentarily.

2. Solder going to the voice coil former could be broken, or the voice coil itself could be intermittent.

Either one of those scenarios has one answer: repair (recone) or replace the driver.

Remove it from the enclosure and drive it fairly hard with a suitable amplifier. If you can make it cut out, can't see any badness on the tinsel wires or other connections to the terminal strip, it's safe to say the driver is bad.

At that point, the best thing you could do is to experiment, and learn.

Sometimes the tinsel wire doesn't make contact to the little wires leading down to the voice coil former. On some drivers those little wires are easily seen, sometimes they are under the dust cap.

Whatever the case, find those wires. A soldering iron is sufficient to melt the glue and expose the little wire. Sometimes a little solder or some paste flux can help you expose it. Once you've done that, find a way to solder the tinsel wire to it - resistor lead, wire wrap wire, whatever. Just make a good connection.

Now reconnect the speaker and test it again, and see if the symptom changes. Fixed? Then you now now how and where the driver failed. If it doesn't fix it, try the other lead.

If either of those happens to make the symptom go away, you could always get real creative and apply some speaker cement and call it 'fixed'. Likely it will not stay fixed, but if your customer is on a budget, or has a gig tonight, you can delay the real repair while you order a replacement or the customer has the cash for the new driver. Really the important thing is that you learn how and where speakers fail. Shipping a questionable speaker is not something I'll do anymore.

Now, if neither of your attempts at a repair yields any success, you're safe to cut the speaker cone out of the basket. Looking very carefully (or sometimes not so carefully) will likely show where the coil was rubbing and failed, or a big black mess, or a single burnt spot. Again, this isn't moving toward a repair, just a good thing to know regarding the failure mode. The answer to the mystery, as it were. Usually you can find the source of the problem. It doesn't take much of a scrape to ruin the insulation on the VC wire.

If the speaker is eligible for recone, cover the magnet gap with masking tape. The recone guy/gal will thank you.

Regards,
-Bill

[Enzo]

Take the speaker out and sit it on something like a table. Clamp your ohm meter leads to the terminals - don't rely on holding them there.

Now press the cone down as far as it will go, it may generalte a little voltage pulse as it moves, and that confuses the meter, but as soon as it stops moving the resistance reading should return. Does it?

Now get behind the cone and lift it as far as it goes. Same deal, is the continuity interrupted?

Now with it sitting there, leave the cone alone, and grasp the tinsel wires and flex them around. Is the continuity interrupted at any time?

I am testing for broken tinsel wires and intermittant connections.

Bottom line it this, you subbed another speaker in and it worked OK, so you know the speaker itself has the problem. it will either be a relatively simple tinsel wire fix, or you need a recone or replacement.

[srvprodigy]

Thanks for the great info guys. Much appreciations!
Enzo, I seriously owe you a beer sometime. Name the time and place my firend. You shouldn't have to give advice for free.
You are Loved! ha-ha-ha.