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Old 17th March 2003, 08:25 AM   #1
Variac is offline Variac  United States
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Default Neodymium is now Mainstream?

It looks like Eminence now has a line of neodymium drivers up to 15"They say the weight is half and the price is "comparable" to conventional (ferrite) magnets.

http://editweb.iglou.com/eminence/em...eo/neomain.htm
Has anuyone actually seen these for sale?

Obviously there has been a breakthrough in the cost of production of Neodymium magnets.

Now many major pro driver makers have neo lines and I'm wondering how this chage in the industry will continue to
affect speaker design. Cheaper shipping so maybe better access to brands normally not worth shipping? Light weight PA systems that are easier to transport?

Less back reflection off magnet structures?
More small tweeters that make concentric designs possible?

But most important, many audiophiles seem to prefer Alnico magnets to ferrite. I wonder if neodymium sounds "better"than ferrite? I remember reading about a possible reason why ferrite might not be the best magnet material. Something about how the field varies so the coil "jumps" rather than having a linear response. Or is it that Alnico is more powerful and can concentrate its force in the gap better? In this case the neodymium might be a step ahead. Or is it all marketing?
Hmmmmmm
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Old 17th March 2003, 06:24 PM   #2
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Lightweight PA speakers--OH YEAH!!!

Unfortunately I think the roadies' union would kill the idea. :-(

I just built myself a PA system (going to be putting verathane finish on sometime this week) using a really clever (IMO) stressed-skin design, so even though they're 3' x 2' x 2', they aren't mammoth to carry around. (The downside is that they are still very large, and consequently, can still cause back problems if you carry them wrong. The next revision will fix this.)

Anyway.

For the next incarnation, I think some high-efficiency woofers with Neodynium magnets would fit the bill perfectly, especially when coupled with the awesome weightlessness of piezo tweeters. (The ones I just built are 3-way, and that was a mistake! The next ones will be 2-way.)

*shrug* I hope my next budget is big enough....
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Old 17th March 2003, 09:38 PM   #3
Variac is offline Variac  United States
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Some home audio speakers were made with honeycomb core panels as used in the aerospace industry. Mainly because they were rigid, not for weight reasons. But a material like that would be very light also. From what I've heard from others, piezo tweeters are best used for the highest frequencies only, so maybe the 3 way was the threorectical right way to go even if it came out flawed. Parts Express and others sell handles which make hauling the speaks around a lot easier. Also gotta have casters on the bottom!

Actually, my main question is if anyone of the type that prefers alnico has heard a neodymium woofer and whether the neo is better sounding than the ferrite ones. Since the new Eminences are called Deltalite, maybe there is an exacy equivalent Delta with a ferrite magnet so the two types could be directly compared.
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Old 18th March 2003, 02:56 AM   #4
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Neodynium has much more magnetic power than ferrite. I have heard the difference is considerably more than two-to-one.

They already have low priced neodynium tweeters that are no larger around then the dome itself. However, these inexpensive tweeters only seem to go down to 4,000 Hz or so.

My prediction is: more coaxial speakers using neodynium tweeters that go down to 2,000 Hz.

It would be nice to see a DIYer come up with a conversion for an Audax, Peerless or Vifa 6 or 8 inch woofer and a neodynium tweeter that crosses over at 2,000 Hz. With the tweeter in the middle of the midrange driver, the imaging should be great.

Thomas W said in another post that mounting a coax tweeter is no easy task. How far to set it in from the front is a problem that requires special equipment.

It seems to me a square wave test would be revealing here.

Anyway, I think that if neodynium makes no other impact, the ability to make high quality coax units would be a great improvement.
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Old 18th March 2003, 03:01 AM   #5
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Anyway, about the extra strength of neodynium. My understanding is that the greatest limit to speaker design is not so much getting the "juice" from the magnet, but getting the magnetic return circuit right. Apparently the best material for magnetic return circuits is hugely expensive. So maybe progress has to be made in the return circuit material before the extra magnetic power of the neodynium can be properly tapped.
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Old 18th March 2003, 04:40 AM   #6
Variac is offline Variac  United States
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There are some high end small neo tweeters. There is a Scanspeak for sure: D2904/6000-01 -perfect for snuggling up against a couple of 4" mids for a MTM that handles midrange up only. If you ground off the flange it is very little bigger than the dome.

Various Audax tweets are small due to Nedymium magnets. not their best though.

In fact, PHL (ex Audax people) supposedly has a 6" with a concentric (Audax) tweeter. I got pretty excited on these pages about it , but then got the word from people I trust (hint: they just came out with a fourway self powered speaker mentioned alot on this site) that the driver wasn't really very good.

It seems that coax's that use the larger cone to load the tweeter are never the very best. I have a lot of faith in the idea Avant Garde is doing with their latest, cheaper speaker: The tweeter has its own horn and sits inside a phase plug for the woofer.
Eton has a speaker with a big heat pipe/phase plug coming out the middle. I'm curious what a tweeter glued on the end would sound like......

There is a pretty big group of respected people that prefer Alnico to ferrite. There seems to be a thory as to why, but I don't think power of the magnet is the issue.
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Old 18th March 2003, 04:44 AM   #7
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We will see more & more Neo. As more plants licence Neo and production volumes go up the price goes down and makes it a more attractive design alternative, which means more magnets, which drives the price down, and on & on...

I wonder when the patents expire.

I have seen a number of discussions on alnico vrs Neo vrs ferrite. Can't remember the detail, but neo & alnico have inherent advantages (except price) over ferrite.

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Old 18th March 2003, 05:27 AM   #8
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Alnico and neodymium are not directly comparable, because they function differently, and give the designer the freedom to use different types of magnetic circuits. I should also add a caveat that the total performance will depend very much on the design of the magnetic circuit, and this may very well be a bigger variable than the magnet material used.

Alnico needs separate pole-pieces to function correctly, while the rare-earth magnets like neodymium can function with or without.

Using a similar grade of iron, an alnico will usually measure as having lower distortion than a ferrite, and particularly the midrange will sound cleaner.

There is another magnetic material called platiron which behaves like a super-alnico, and sounds like it, too. The price of this stuff is hugely expensive, however, and so far, only two phono cartridge manufacturers - Koetsu and Lyra (me) - have used it in audio so far. I reckon that this would make an amazing speaker magnet, but I don't have the finances required to sponser such a project.

On to rare-earth magnets. If such are used with polepieces, the distortion figures and listening results usually will both be better than a ferrite. OTOH, samarium-cobalt, presidymium and neodymium all sound different from alnico, and they also sound different from each other. Depending on personal preferences, some listeners may like the alnicos, while others may choose one or another of the rare-earths.

What I particular like about the rare-earths is their ability to be used in a magnetic circuit without any polepieces whatsoever. For a given design, improving the grade of the polepiece material nearly always provides better measured and subjective results, but in my experience, designs that eliminate them completely provide the lowest overall distortion.

But there are other prices to be paid. First, the efficiency goes way down. Next, neodymium is far more sensitive to temperature than alnico. Above 70 degrees C, for all practical purposes it is non-functional as a magnet material.

For applications where these issues are not a problem (MC phono cartridges), no-polepiece neodymium circuits work better than anything else that I have tried. But realistically, it will require more time before such designs can be used in speaker units.

Pricing-wise, the weaker grades of neodymium are becoming far cheaper than they used to be, but the most powerful stuff (BHmax 50 and 52) is very expensive.

http://www.ssmc.co.jp/what0205.html

regards, jonathan carr
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Old 18th March 2003, 09:11 AM   #9
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Default Re: Neodymium is now Mainstream?

Quote:
Originally posted by Variac

Something about how the field varies so the coil "jumps" rather than having a linear response. Or is it that Alnico is more powerful and can concentrate its force in the gap better? In this case the neodymium might be a step ahead. Or is it all marketing?
Hmmmmmm
Seach for Barkhausen noise. There was a link in one of the Manger threads to some page called celticaudio with an article called "Putting the science back into the loudspeaker". Barkhausen noise is the jumping of domain borders under an external field. The author makes the case that neodymium, being conductive unlike ferrite, can screen the external field generated by the current in the voice coil. I doubt that is is sufficiently conductive to be as effective as a copper ring on the pole piece. Copper is roughly 20x more conductive than typical iron alloys, so half a mm of copper do the same screening as 10 mm of iron. Also, I think what is happening in the iron return circuit is more important that what is happening inside the magnet.


Quote:
Originally posted by kelticwizard
Apparently the best material for magnetic return circuits is hugely expensive. So maybe progress has to be made in the return circuit material before the extra magnetic power of the neodynium can be properly tapped.
It is true that there are various grades of iron which can transmit a maximum flux of 1.2 to 1.5 T (I have seen this last figure quoted several times but I doubt there is iron that can have a magnetization that strong). The limit of what ferrite can do is around 1.3 T. whereas Neodymium can generate up to 3.5x the flux. So while the maximum Bxl that can be achieved for a certain geometry may slightly depend on the grade of iron used, the important part is that a properly designed Alnico or Nd system will drive the return circuit well into saturation. Having a saturated iron system is a great thing! It means that the magnetization of the return circuit is not modulated by an external field that is smaller than the amount that the magnet flux exceeds the saturation flux of the iron. So the field in the gap is just the linear superposition of iron and coil field. The coil field cannot cause the iron field to sag. So this reduces intermodulation distortion.

Besides this, we don't have to worry about Barkhausen noise in the iron or the magnet (a saturated return circuit cannot transmit the external field back to the magnet). What is more, voice coil inductance is lowered because an iron core that cannot react the the VC field does not increase its inductance.


Jonathan, have you been able to make these comparsions on one driver, just by exchanging the magnet? Do you have any explanation for the sound differences you have perceived?



Regards,

Eric
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Old 18th March 2003, 09:19 AM   #10
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I should add that in the 2nd/3rd and 5th harmonic measurements that the two speaker builder magazines in Germany publish regularly, there was no systematic trend that Nd tweeters, mid-woofers or woofers performed systematically better than conventional drivers. They were good average to very good, but not as low as the best ferrite designs.

Audax has a line of Nd tweeters with low distortion, but their ferrite models appear to be just as good.

Scan speak has a new 12 cm revelator out with Nd magnets. Distortion performance is average. The 15 cm ferrite revelator is better but still not excellent.

This may mean that some designs have just enough magnet strength to get the iron close to saturation, as ferrite does. So maybe, these manufacturers are saving on the amount of Nd.

Or it may mean we are doing the wrong kind of measurements. Siegfried Linkwitz maintains that IMD measurements are much more revealing than HD measurements.
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