Recently I had the great honor of having a pacemaker inserted into my poor old body. Among warnings to avoid various microwave emissions and MRI and other strong magnets, was the caveat about keeping away from large stereo speakers.
I know they have big ol’ electromagnets. The question I have, is when there is no signal being sent to them, are the magnets still active?
I have no powered subwoofer, just two rather large speaker boxes with woofer, mid-range and tweeter. When not being used, is it safe to be close to them?
You are partly right about the electromagnets in speakers. Each one has a big fat permanent magnet, active all the time. There is also a little coil of wire attached to the speaker cone. When the signal goes through that coil, it becomes an electromagnet, and it moves, relative to the big magnet. That’s what makes it talk and sing.
Now in the age of home cinema many stereo speakers are shielded so that they do not interfere with CRT TV sets. My guess is that they would be less likely to interfere with pacemakers also (though not sure, if I were in you position, I would want to test this out). Now that CRT sets are no longer the thing to have, maybe shielding will wither away too.
I second ticker’s “less likely” hypothesis. Big picture tubes are sensitive to magnetic fields, because electrons in the electron beam curve in magnetic fields. I think they are sensitive enough to change a little if you reorient the set with respect to the Earth’s magnetic field. So if the speakers don’t change a TV visibly, it’s hard to imagine they’re going to mess with your pacemaker.
It would probably be hard to build a pacemaker that didn’t mind the magnetic fields in MRI machines, but those are strong, IIRC around a Tesla or two of field intensity. But Earth’s magnetic field is I think 5e-5 T, and the speakers are something like that if they’re compatible with picture tubes nearby.
So I bet you’re OK with them.
Of course, I’m not betting anything, much less my life.
What’s your pacemaker’s web site say about it?
Also, if you get a compass, place it on the table, then bring the speaker into the room, how close does it have to get to overwhelm the background Earth’s magnetic field? Well, I mean, if some volunteer does those things for you. It’s hard to imagine your pacemaker cares about fields about as strong as the one we already live in.
Thanks, all, for the interesting info. As my speakers are about five years old, they well may not be shielded.
In any case, as interesting as these suggested experiments are, I think I’ll just forget them and give the things a wide berth. If anything ever has to be done to them, I’ll let my wife do it. That is, until she needs a pacemaker too.