Magnet? Magnot.
Apr. 10th, 2014 01:26 am![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
greatbear(Caution: electronics geekery ahead, if that ain't yer bag, skip to your next post)
Planned obsolescence? It's alive and well, even if it wasn't intentional.
Once again, out of the blue, I notice that a speaker has gone bad, this time in a portable TV set. The little set has a pair of them, the right channel was dead.
This in the third speaker that has failed in the fashion, and I've had hard drives and a tiny DC motor fail in the same way rather recently. What do these all have in common? Magnets. Small permanent magnets. And in all these situations, the magnets were all "rare earth" neodymium magnets. I love me some neodymium magnets. Tiny, strong as shit, make so many things more efficient, lighter and more powerful, blah blah blah. In my latest repair job, I noticed my little 9" Panasonic combo TV/DVD player was missing the right channel (don't laugh, this tiny set, which I used to take camping, is the third most-watched set in the house, it sits atop my studio/AV workstation desk, along with a DTV converter box to make it usable). The right channel was a scratchy, low volume mess typical of a stuck voice coil. This time, I had a pretty good idea what was going on, as I had replaced two speakers in two completely unrelated radios with the same problem. It's not as if I was blaring these sets at full volume or otherwise misusing them, quite the opposite, in fact, these devices are taken good care of.
In all these units, the speakers resemble those old-school alnico magnet speakers you'd find in any one of a bazillion transistor radios from decades past. These have the advantage of having a small magnet structure that is self-shielding. But rather than the slug of alnico making up the magnet inside the cup, these speakers now use a neodymium disk magnet along with a similar-sized pole piece atop the magnet to concentrate the field in the gap. What look like cheap little speakers are instead rather efficient and make strong sound from rather small amplifiers. These speakers have decent power ratings for their size (the TV ones are rated 1W, the radios were 3W, all speakers from different makers were 3") and belt out reasonable sound for what they are. What seems to be the trouble with all this cheapass speaker goodness? Neodymium magnets have a coating, in most cases a shiny metallic silver nickel or ceramic coating. Typical strontium magnets, those dark grey disks sandwiched between two pole pieces, are almost never coated. The material is inert, after all. The neodymium material, which is actually an alloy of neodymium, boron and iron, pulverized into a fine powder and sintered (pressed together and heated with a bonding agent) corrodes easily when exposed to air. These magnets are sealed to prevent this from happening. Well, such is the case in a perfect world...
Apparently these magnets had little if no coating to seal out the air, and it didn't take long for these magnets to revert to their original pulverized metal components. The magnets literally turn to dust, filling the magnetic gap with magnetic powder and jamming the voice coils in place. Of course, the mushy remains of the magnet become unbonded from the structures and flop around in the gap as well, freezing the VC even tighter. Nothing looks wrong with the speaker from the outside. Cutting out the cone, spider and coil, and lifting out the remains of the magnets reveal all. The magnet resembles a half-dissolved metallic aspirin sitting in a puddle of water.
I was able to root around in my stock of parts and find a decent pair of magnetically shielded 3" speakers to replace the ones in the television (though they just fit, being that the magnets were ten times the size of the originals) and everything worked out well and cheap (as in free), since I harvested the little speakers from a set of PC speakers I was discarding. I've also discovered it's damn near impossible to find these small commodity speakers that used to hand on the walls at the local Radio Shack for years until around 2000 or so. Even my usual parts suppliers don't bother with them anymore.
Think of all the stuff made with neodymium magnets these days. Anything with a hard drive. Many modern cordless power tools. Headphones, cell phones. anything with a motor, like DVD players. Motors like the starter in cars. You name it. This set is about ten years old, and the magnets died. In a couple cases where I had magnetic flashlights with these disk magnets, the coating became scratched and the magnet corroded in a matter of months.The dust is highly magnetic and can end up in places where it might not be wanted and difficult if not impossible to remove. Some older hard rives became unusable, and when I opened them up, the magnets were toast.
I have a feeling this is going to be a widespread problem. But, hey, since no one keeps anything beyond ten years anymore, it will just end up being tossed anyway. I'm not like that. In most cases, I keep stuff a long time, especially tools.
And you thought Juggalos had issues with magnets.
Planned obsolescence? It's alive and well, even if it wasn't intentional.
Once again, out of the blue, I notice that a speaker has gone bad, this time in a portable TV set. The little set has a pair of them, the right channel was dead.
This in the third speaker that has failed in the fashion, and I've had hard drives and a tiny DC motor fail in the same way rather recently. What do these all have in common? Magnets. Small permanent magnets. And in all these situations, the magnets were all "rare earth" neodymium magnets. I love me some neodymium magnets. Tiny, strong as shit, make so many things more efficient, lighter and more powerful, blah blah blah. In my latest repair job, I noticed my little 9" Panasonic combo TV/DVD player was missing the right channel (don't laugh, this tiny set, which I used to take camping, is the third most-watched set in the house, it sits atop my studio/AV workstation desk, along with a DTV converter box to make it usable). The right channel was a scratchy, low volume mess typical of a stuck voice coil. This time, I had a pretty good idea what was going on, as I had replaced two speakers in two completely unrelated radios with the same problem. It's not as if I was blaring these sets at full volume or otherwise misusing them, quite the opposite, in fact, these devices are taken good care of.
In all these units, the speakers resemble those old-school alnico magnet speakers you'd find in any one of a bazillion transistor radios from decades past. These have the advantage of having a small magnet structure that is self-shielding. But rather than the slug of alnico making up the magnet inside the cup, these speakers now use a neodymium disk magnet along with a similar-sized pole piece atop the magnet to concentrate the field in the gap. What look like cheap little speakers are instead rather efficient and make strong sound from rather small amplifiers. These speakers have decent power ratings for their size (the TV ones are rated 1W, the radios were 3W, all speakers from different makers were 3") and belt out reasonable sound for what they are. What seems to be the trouble with all this cheapass speaker goodness? Neodymium magnets have a coating, in most cases a shiny metallic silver nickel or ceramic coating. Typical strontium magnets, those dark grey disks sandwiched between two pole pieces, are almost never coated. The material is inert, after all. The neodymium material, which is actually an alloy of neodymium, boron and iron, pulverized into a fine powder and sintered (pressed together and heated with a bonding agent) corrodes easily when exposed to air. These magnets are sealed to prevent this from happening. Well, such is the case in a perfect world...
Apparently these magnets had little if no coating to seal out the air, and it didn't take long for these magnets to revert to their original pulverized metal components. The magnets literally turn to dust, filling the magnetic gap with magnetic powder and jamming the voice coils in place. Of course, the mushy remains of the magnet become unbonded from the structures and flop around in the gap as well, freezing the VC even tighter. Nothing looks wrong with the speaker from the outside. Cutting out the cone, spider and coil, and lifting out the remains of the magnets reveal all. The magnet resembles a half-dissolved metallic aspirin sitting in a puddle of water.
I was able to root around in my stock of parts and find a decent pair of magnetically shielded 3" speakers to replace the ones in the television (though they just fit, being that the magnets were ten times the size of the originals) and everything worked out well and cheap (as in free), since I harvested the little speakers from a set of PC speakers I was discarding. I've also discovered it's damn near impossible to find these small commodity speakers that used to hand on the walls at the local Radio Shack for years until around 2000 or so. Even my usual parts suppliers don't bother with them anymore.
Think of all the stuff made with neodymium magnets these days. Anything with a hard drive. Many modern cordless power tools. Headphones, cell phones. anything with a motor, like DVD players. Motors like the starter in cars. You name it. This set is about ten years old, and the magnets died. In a couple cases where I had magnetic flashlights with these disk magnets, the coating became scratched and the magnet corroded in a matter of months.The dust is highly magnetic and can end up in places where it might not be wanted and difficult if not impossible to remove. Some older hard rives became unusable, and when I opened them up, the magnets were toast.
I have a feeling this is going to be a widespread problem. But, hey, since no one keeps anything beyond ten years anymore, it will just end up being tossed anyway. I'm not like that. In most cases, I keep stuff a long time, especially tools.
And you thought Juggalos had issues with magnets.
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no subject
Date: 2014-04-10 07:40 am (UTC)no subject
Date: 2014-04-10 09:38 am (UTC)no subject
Date: 2014-04-10 12:55 pm (UTC)If speaker and electronics companies are truly interested in making a better product, perhaps you could patent a better coating for those neodymium magnets.
no subject
Date: 2014-04-10 02:16 pm (UTC)no subject
Date: 2014-04-10 07:36 pm (UTC)no subject
Date: 2014-04-11 09:07 am (UTC)One of the reasons companies that sell NIB magnets tell people not to let them slam together - aside from the potential for shrapnel, as they're rather brittle - is that if the coating (the ones I have are nickel plated) gets damaged - the process you describe starts.