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Many people know that CHINA is the worlds #1 source for the rare earths used in many applications including the worlds strongest magnets.
Well, China restricts exports and thereby not only keeps the price UP, but makes less expensive uses non-starters.
I saw on the news / sci channel or discovery or history last nite that a large, open pit mine has been opened in the good ole USA. This is good and will make us somewhat less dependent on the Chinese.
Rare Earths are neat. Each in that series.....Elements 57->71 are not only difficult to tell apart, but have very similar chemical properties. They ALL have 2 electrons in the outer 'binding' shell. Additional electrons are added to vacancies on lower shells, as you go up in atomic number.
One thing I didn't know what that Neodymium is only PART of the magnet to which it gives its name. The majority is good old Iron with a trace of Boron. Both fairly common.
Why is this of even passing interest to a stereo / hifi addict? Well, speakers sensitivity can be predicted from magnet strength and the gap distance. A very strong magnet, very close can make a very sensitive driver, indeed. My poor panels? They use something not any better than refrigerator magnets. I've always wanted a panel with very strong rare earth magnets.
A very sensitive speaker needs far less amplifier, which is an attractive idea to some.
Be careful, you can damage yourself with a 2-magnet 'pinch' if you get in the way! Or, even damage that old CRT TV or Monitor you use in the garage.
Too much is never enough
Follow Ups:
In addition, India, Australia, Sri Lanka, and Brazil are also major producers of neodymium. Neodymium is the 26th most abundant element on earth, about the same as Copper. Cost is incurred primarily because refining costs are high: as you noted, the rare earths all mimic each other with the two outer shell electrons.
The other rare elements are critical in the products of flat screen video sets, and thus critical for ipads, Kindles, phones and such: That's how China was able to hold Japan hostage in their recent trade bargaining talks. Neodymium was in great part responsible for the leap in computer memory and motor speed.
Neodymium is already being used for speakers. One of the earliest was Lowther and their DX series of speakers, although sensitivity is not that much increased over their more conventional offerings. There are quite a few tweeters which also use the neodymium type magnets.
There's an excellent book entitled "Nature's Building Blocks" by John Emsley which goes through all the elements one by one and explains them.
Stu
If I remember correctly, the Lowther has a field strength of 1.2 Tesla. That is way strong,
Again, if you want a more sensitive driver, increase in magnet strength is maybe the easy way?
I don't know. But the OTHER way is to decrease the gap to as small as you can maintain in production.
For planar drivers, increase in magnet strenth and increase the 'gap' may increase power handling capacity, since you won't get mylar slap quite so easily. This would be with no net increase in sensitivity.
Thinking about panels....and possible improvements is what got me going down this path.
Too much is never enough
Lowther DX drivers have the ferric coating and the VC gap is quite small. Just goes to show that that there are many ways to skin a cat.Stu
PS can you imagine the issues you would have with a planar speaker full of neodymium magnets? I suspect your vacuum cleaner hose, among many other objects would be stuck to it.
Edits: 04/09/12
Fortunately, the polarity reverse with each magnet srip. There are some planars that do use neodynium magnets -- Graz's super Apogees, the big Wisdom in-walls, the smaller BG "Neo" and Eminent Tech drivers. Also some true ribbons.
The reason they aren't usually used in big planars is that they're so expensive. The more efficient speaker would cost the customer more than a larger amp would.
I hadn't thought of that. I guess if you were within 10 yards of a CRT TV you'd mess it up, too.
Not to mention your fillings.
The vac? That's a disaster waiting to happen.
how about on a push/pull panel? would that 'short out' the magnets?
Too much is never enough
My Lowther DX-4 when I moved it to within 2 feet of my computer CRT turned the whole screen into a prismatic array. My greatest fear would be that the magnets could attract something sharp and tear into the diaphragm.
Stu
If I ever come over, I guess I'll have to keep my distance. That steel plate in my head, you know!
Too much is never enough
Graebener planars ( still available at Parts Express I believe) use a mess of BIG neo magnets, arranged so the mag field is kept within the speaker. I have some discards that David Graebener gave to a friend.. Scary strong, foot-long by 1/2 inch square monsters!
cheers
Adam in Ashland Oregon
That is an expensive $$$$$ magnet if made os neo. Also, strong enough to be dangerous while ALSO being somewhat brittle.
How do they sound? Sensitivity?
Too much is never enough
Those are the BG's that Satie uses (Neo 8, these are the bigger brother Neo 10). They apparently sound excellent.
The ones I heard were in an amazing home theatre demo, coupled with attic-mounted tapped horns. Very dynamic, great imaging.
According to the spec sheet below, 93dB sensitivity.
Yes, to both of the above.
China in particular is not our 'friend' or only to the extent they can get the US dollar while leaving the Yuan as cheap as possible. If the Chinese Yuan were to float to a more real value, some of the trade imbalance would go away. Weak Washington Pols? World Bank? IMF? 'Them'?
As for the pinch? Consider yourself warned! I suspect such behavior is WHY Magnepan does NOT use such magnets in the construction of panels. Buy a couple DB of sensitivity? For Sure. Raise prices to cover additional cost? absolutely. Higher insurance claims from the magnet handlers getting 'pinched'? Yes again.
Too much is never enough
You get an amazing sensitivity increase. But Wendell Diller's answer to your question is the same as his answer to just about any question about why something isn't in Maggies: too expensive!
It is ironic that many of the metals that are making our modern world are experiencing 'shortages' - though mostly what they are facing is barriers to market/profit motives. Many of these metals are also used to make the high-strength steels for Oil & Gas exploration, pipelines and power plants. From a geological perspective, there are many places on earth where these can be found; however many of the mining companies do not wish to be fettered in their extraction efforts, so, they are not producing these materials in the continental US or some of the other 1st world areas where they could be.
There also has not been the concerted effort to develop recycling programs for these materials that could mitigate these effects.
Happy Listening
At our lab we've been working with some 3 inch x 1/4 inch ring magnets. I went to pick one up from a group that were carefully laid out separated from each other. It decided it liked its neighbor more than me, the neighbor jumped up about 6 inches, and the two clamped themselves onto my ring finger. Reflex response took over and I pulled the finger out, but it looked like I had smashed my finger with a hammer. Three days later the lovely purple hue is starting to subside.
This all happened WAY faster than I could have reacted to.
Kids, be careful out there!
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