Here’s a question I received recently that I thought could use a Mailbag post:
Can an antique permanent magnet speaker catch fire?
Interesting question. Short answer? Maybe. Longer answer? Well:
It really depends what the source of the fire is. Pretty much all speakers are made of some flammable parts like plastic or nylon wire lead insulation, a paper or plastic cone, and potentially some other fabric. Something would catch fire and burn if you held a match to it, but I doubt that’s the kind of failure you’re talking about.
A permanent magnet speaker lacks the high-current, high-voltage field coil sinking 50W+ of heat directly into the frame so there’s much less to go wrong. Such speakers are typically made of a metal frame, thin carefully wound voice coil, and the voice coil cover, cone, dust cap, and surround. Some models might also have an output transformer mounted to them if they’re very old. A failure in the output transformer might heat up and release some smoke, but the winding would likely go open and cut the power before anything really bad happened.
The voice coil itself, similarly, is unlikely to heat up enough to catch the cone and insulation on fire. Nearly impossible for most kinds of speakers you’re likely to encounter. The voice coil, while it does carry some current, needs to be light and flexible enough to respond quickly to audio and move the cone. Even in the event of a major failure that put a high voltage with lots of available current onto the voice coil,, such as a primary-to-secondary short in an output transformer or a shorted output transistor, it’s much more likely the voice coil would blow out and go open in a single loud “whomp” of the speaker before anything put off a lot of heat.
A vintage cabinet speaker with a crossover network is similarly unlikely to set a speaker driver on fire, although there are a few more possible failures in the crossover network itself. Poor ventilation, incorrect parts selection, or both can cause crossover components to heat up and potentially burn. It’s very unlikely to be a problem with any quality speakers, but speakers which haven’t been refurbished and have dead capacitors in the crossover network – or are being driven far over their power ratings – could fault in a way that releases some smoke and potentially ignite if the fault isn’t caught. It’s happened before. (Don’t leave your stereo playing if you’re not there to listen to it!)
So, in conclusion: an antique permanent magnet speaker is very unlikely to catch on fire, but you should follow safe handling practices for antique and vintage electronics anyway, as failures on older gear can be a lot more dramatic than they are today.
Speaking of vintage speakers, if you do need your crossovers repaired in a vintage speaker, Rain City Audio can take care of it for you.