Is my driver broke??? how to tell??

[panduro]

My broder inlaw killed an old active diy "subwoofer" watching the latest Rambo dvd a while back.
He said that the súb exhaled some smoke before the silence.

I checked the amplifier for burn markes and their was one fairly big burn marke on the amplifier(hypex 80) pcb.


pushing the cones, no sound.
a small 1,5V batteri to plus, made a little sound from the speakers when tapping the minus poles with the speakerwire, and making xcursion. allmost identical sound from both drivers.

so i thought the drivers were fine.

so that was an easy fix, down to the parts dealer and get a new amp(got it realy cheap luckylie).

mounted it, turned on the sub, loud grouwling sound, smoke and then silence. another dead amplifier... god dammit i felt stupid.

got angry and kicked the sub to the kerb. I kept the 2 small 6,5" drivers (vifa pl18WO09).


how do i check which ones broke(or both), as i dont want to put my nakamichi or holfi amplifiers at risk?

best regards

panduro

[AllenB]

Is it possible that the voice coils overheated and some windings shorted? Measure the DC resistance across the terminals and compare with spec.

[chris661]

Sounds about right.

I cooked a speaker today, (cheap + nasty one, sounded awful). Turns out that a couple of shorted coils won't stop a speaker going. It let a lot of smoke out, but it carried on for a while. But yeah, some of the windings had definitely shorted as it (on bass notes) activated the over-current relay in my amplifier. Turned it down again, and you wouldn't know the difference.

I'd replace both drivers. It's unlikely that just one has suffered damage.
Chris

[panduro]

Hi AllenB, thanks for the respons.

The specs: voice coil resistance 5,8ohm.

mine: 7,2ohm both of them! to the daft part of this conversation, could you translate the result to plain english

best regards

panduro

[AllenB]

Did you subtract the resistance of your meter and leads? If not, short the leads together and take the reading, then subtract this from 7.2

It sound as if your drivers may be OK. Can't be sure though. Maybe you should try listening to your drivers through another amp, but use resistors in series (anything above 8 ohms, for example to protect the amp), and keep the volume down.

[panduro]

It measures 1,6ohm, so 7,2 - 1,6=5,6ohm.

hmm ok, dont have any resistors. guess im gonna have to wait til i can get some.

would it have a higher or lower dc resistance than in the spec if damaged?

best regards panduro

[AllenB]

Either way would be a problem.

If your DC resistance is good and your cone moves freely, I can't think of any 'typical' reason that your replacement amp should fail.

[panduro]

Hmm i apparently like putting my gear at risk,

i tried one drivers at a time connected to a nakamichi pa-5s2 though a digital xover(behringer dcx2496) from 200hz to 5khz at low volume, turning the volume slowly up, nothing weird from amp or drivers. just to check because drivers sound different when there's no enclosure i tried and old b&w matrix 6,5" driver. it sounded the "same".

then i tried 100-5000hz, same result.

50-5000hz, almost same result, one of the 3 drivers had a very small blur to it.

then tried 50 to 200hz just laying the drivers on the matrix 805 enclosure(vifa driver a bit bigger than b&w driver). one driver sounded ok, one made alot of bad noises, but only when I turn the volumen up.

so i guess thats the answear, one driver is dead, one still lives.


thanks for all answears

panduro

[AllenB]

With no enclosure, any driver will move a lot down near its resonance. For a 6.5" driver this might be near 50Hz. If the voice coil reaches too far and touches the end stops it will make a loud flapping noise which is normal.

On the other hand, if this happened before, the voice coil former might have changed shape so it makes more noise, and, if it overheated then some of the glue holding the cones may have melted.

[panduro]

Hi allenB,
yes, so its dead, oh well gott one driver left to play with.

best regards

panduro