Speaker help?! -please-

[gav]

Personal speaker problem, -i'm totally clueless-
*any help atall,is hugely appreicated*
basicly my brother had a party and when i got back hes managed
to break the speakers - a pair of JPW, 70 watt -
apparently they 'just stopped working'
and i havent been able to find out what happened.
I've been desperatly searching the net trying to learn
how i can fix them. I'm totally un-willing to throw them
out unless i'm totally sure they cannot be fixed
-having said that i cannot afford to send them to a repair shop.
i'm hoping its going to be a case off replacing a component
i'm handy with a soldering iron but i dont know what needs to
be replaced.
visably there is no damage to the voice coil,
also no visable damage to the cone, and it can still move,
i cannot see any broken wires atall
... yet still no sound can be heard when connected, not even hiss.
heres some pictures

if you have any idea of what i can do, i will be VERY greatful for your ideas.

 

[avkid]

I'm going with the crossover being messed up. Possibly vibrated a cold solder joint to the point of failure.

 

[Eboy87]

Are you handy with a soldering iron? You should probably touch up all the solder joints on the x-over. Also, the tinsil leads might be broken down around near the gap. Unfortunately, those are a little harder to check. But from the problems you describe, it sounds like power isn't getting to the voice coil at all.

 

[gafftaper]

No visible sign of damage to the speakers and both of them suddenly stopped working. That sounds more like a problem in the amp and not the speakers to me. Did you try a different speaker on the system so you know that the amp itself isn't toast? Check for fuses.

 

[TimmyP1955]

It looks like a simple first order crossover. For both drivers to be dead owing to the crossover, both the cap and the choke would have to be kaput, which is not likely.

Touch - just for a second - a battery (9V or 1.5V - either will do) across the woofer terminals. If it does not pop, the woofer is dead. Do the same with the tweeter. Pop is good, no pop is bad.

 

[gav]

thanks for all your help guys, i really apprciate it.

The amp is fine.
-But, Timmy, i hav just followed your advice with the battery and no pop
from both woofer and tweeter.
i'm going to assume this means i'm screwed?

 

[Peter]

Another thing to try, can you place an ohm meter across each pair of the terminals going into the drivers and see what the reading is? Make sure nothing else is connected when you do it, but if you get 0 Ohms, ya, your not in a happy place, but if you get more like 2-10 Ohms at least you dont have a solid block of copper in the driver!

PS: Someone else can jump in and verify my #s are correct, that's what you'd expect to see on a larger PA speaker, but I think these speakers shouldnt be too much different.

 

[Chris15]

Peter, I'll help out. For an 8 ohm speaker, I'd be expecting a DC resistance of about 5 ohms. Figure a proportional sort of number for other impedance drivers.

Now, just because the voice coil appears to be fine doesn't mean it is. I've seen dead voice coils devoid of obvious damage. Now here's another trick that might be worthwhile... disconnect your drivers. Then you can try the battery trick, (that's a nice trick to check if all your boxes are in phase also) or you try touching the amp outputs directly to the drivers, low volume. Only keep them there for long enough to see if the drivers work. If the drivers are fine, something in the crossover is dead, otherwise, you've found your dead drivers. The cabling between input & cross over could be problematic also...

Just remembered another thing. If these were being driven hard and aren't so new, there might be hot glue in the crossover. Old glue, when hot, can become resistive so it may have shorted out your connections. Not all that likely, but definitely possible. Some cabinets are known for desoldering themselves under duress and setting themselves alight... literally.

 

[gpforet]

If the driver is toast, you'll see either 0 ohms (shorted), or infinity (open windings). You're right that anything between 2 and around 10 would indicate that the driver coil is o.k. The reason then numbers can't be exact is that the speaker is rated in impedance (which is resistance to AC and which changes based on the frequency of the voltage), and the ohmmeter measures true resistance (resistance to DC).

Since the person wasn't there, it is possible that the speakers were UNDER-driven with clipped power, and each driver failed individually.

 

[Eboy87]

Since the person wasn't there, it is possible that the speakers were UNDER-driven with clipped power, and each driver failed individually.

A very good point; under-powering speakers is the fastest way to kill 'em. Well, fastest would be to play a very loud transient at an ear splitting volume, but you get the idea. I've seen more drivers fail from cooking the VC from under-power, as much as an oxymoron that seems. I've also seen more drivers fail parallel parking than anything else.