Posted by Curtis H. List (Too Tall) on August 29, 2002

I have seen it once while we were testing a cheap 8" with a 300watt amp.
A friend of mine managed to set some Perkins cabinets on fire mixing Savoy Brown. He did it by trying to get a little more 600Hz out of the snare drum.

The voice coil has resistance so the more power that goes through it the hotter it gets. The reason we don't see it more is something else usually fails first.

It usually isn't low frequency because the driver hits physical Xmax and tears itself apart before it can melt. As they make drivers that can move further this may change. Something to watch for.

Next when the insulation fails from the epoxy melting the coil shorts or parts because it detaches from the former and it is dead. So the epoxy has to keep the coil insulated and held to the former long enough for the temp to go to 451F (Or whatever temp it takes to bring the epoxy or cone to flame). To many it is a worthy goal to shoot for. ;-)

The typical fire in a box is from inductors on woofers or resistors in series just about anywhere. I just scraped some ugly black lumps off a factory EV 1"/15" xover that used to be the volume control on the horn and a 50-ohm (you got to be kidding) resistor in parallel with a cap on the high xover.
Neither part had a fighting chance.

Too Tall


Posted by Marcus on August 31, 2002

I got it once with a yamaha board (The GA32 I think). If you catch the group/aux buttons just right they latch in a sort of mid-way position and set up ultrasonic osciallation. Turned several wedges into bona-fide smoke machines.

Marcus

Posted by Jim McKeveny on August 30, 2002

If I'm not mistaken, some early EV 180's had a knack for catching fire. While the electrical parts were OK for the nominal 1K power rating, in a failure mode arcing could and would set the cones alight. Nightmare scenario : mid-show, wood boxes in the air, flown by polyester spansets!!

EV's response to this was some nomex around the filament leads and FUSES(?) on them! Where'd the 1K rating go?


Posted by Curits H. List (Too Tall) on August 30, 2002

Typically the times I have flown cabinets with span sets they have been small and not very high up.

I never really thought about flown cabinets catching on fire from the inside. Pyro, yes, but not from the inside
Jeez!

Too Tall


Posted by J Ranger on August 29, 2002

I have never had it happen to me, nor seen it. Though, I know that in the right circumstances, it can happen. No DC, all DC does it push the cone to full excursion. It has to do with the voice coil reaching critical and setting the spider assembly on fire, from there glue can and will be set on fir, is its resin based, and explode itself out of the spider area.

How do I know this, if it hasn't happened to me, common sense. The voice coil is at pretty high energy levels (they do have a cooling vent in the cap), this combined with the proximity of the fabric web and glue/epoxy secured wiring ...

Anyway ... I would have wondered what is up, before it got to that point .. just and observation, the low end of the smile would send the low end drivers into some wild harmonic energy.

J Ranger