Alnico

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amo

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Joined 2003
#1
An externally hosted image should be here but it was not working when we last tested it.


I was admiring this sexy driver from Davis Acustics on the PE site today, when I realized that I really do not know what are the benefits of using Alnico drivers. Can someone please comment on this? Are they usefull in open baffle or dipole applications? Are they worth it if you are going to limit their bandwith in a 3 or 4 way system? If you are driving them directly from an amp?

Thanks!
 
#2
I was very atracted to this driver also, befor I biught some Phy-HP. I've never heard them but I think it's a pretty damn good driver. It's originally designed as a mid driver for big systems but will do very well in a small TL enclosure. You can use it up to 4kHz without any problems. It has a very high Qm of 12 or something, wich indicates it's got a very lively sound, that's also what an alnico magnet does. Lively and dynamic. Might be a very good partner for a ESS Air motion transformer.
 
#3
One of the oldest members of our magnet family, Alnico remains the workhorse of the permanent magnet industry and can be relied upon to deliver impressive flux density at an economical price. Alnico also boasts the lowest temperature coefficient of any commercial magnet material (.02% per degree centigrade) allowing for excellent stability over a wide temperature range.
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So, the best flux density, stability and temperature resistance for the money.
 
#4
It has been mentioned in this forum that far from being an archaic material that was surpassed by something superior, alnico simply became too expensive so it was replaced by ferrite.

My question is this.

Suppose I have two ten inch woofers. One, with a ferrite magnet, has a 2" voice coil diameter, a .25 in, (6mm) linear throw, and a Bl of 10.

The other has similar specs, but uses an alnico magnet.

My question is: how much would the ferrite magnet cost for such a speaker? And how much would an alnico magnet cost for such a speaker?

Of course, approximations are welcome. Estimate the clearance between the voice coil former and the pole piece, etc. I am just looking to assess the relative costs of alnico vs commonly used ferrite grades in speaker applications.
 
#6
markp said:
Alnico cost up to ten times as much as ceramic per unit.
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Thanks, Mark. But per unit of what? Weight? Magnetic strength?

If you use a smaller magnet to get the same Bl, that would affect the cost, I am sure.

For all the discussion of alnico vs ferrite, I am just wondering what the cost really is, and how much more expensive it would make the speaker.
 
#9
Magnets have many properties, most of which I don't know or don't remember. However, I do remember that AlNiCo can be demagnetized far more easily than ferrite, which is why much taller magnets are required for the same purpose, even though they're stronger per unit of cross-sectional area.

Casey, Samarium Cobalt magnets are used where performance at high temperatures is required, eg: in industrial motors. You could also use some metallic material that can carry a lot of flux as a buffer to protect neodymium magnets from high temperatures, not that the magnets heating up to 200 degrees C would ever be your biggest problem.

CM
 
#10
CeramicMan said:
which is why much taller magnets are required for the same purpose, even though they're stronger per unit of cross-sectional area.
CM
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Sorry CM, but simply not the case. AlNiCo magnets can had handle
much higher flux than ceramic, of the same order as iron, its the
fact that ceramic magnets can't which is why they are flattened.

🙂 sreten.
 
#12
sreten said:


Sorry CM, but simply not the case. AlNiCo magnets can had handle
much higher flux than ceramic, of the same order as iron, its the
fact that ceramic magnets can't which is why they are flattened.

🙂 sreten.
Click to expand...
Look up Hc: Coercive Force and Hci: Intrinsic Coercive Force. In this sense even the worst ceramic magnets are better than the best AlNiCo ones.

Note: This is not the same as flux density properties.

I agree that the lower flux density of ceramic magnets means that they need to be wider, like I already said in my previous post. But because ceramic magnets are much harder to demagnetize, they last longer, and they can have bucking magnets attached. To partly counteract this weakness of AlNiCo magnets, designers need to make them a lot taller, which is consistent with speakers and photos that I've seen.

CM
 
#13
About alnico

In the mid 70's the price of Cobalt went up so much that companies had to change for ferrite magnets. But Alnico had some advantages : they were smaller, shielded and recognized as having less distortion than ferrites due to flux modulation reduction. But they were slightly sensitive to demagnitization because of heat. JBL was one who recognized this and took the problem in a different way since the cobalt price affected them also. In the beginning of '80s they redesigned all their driver with ferrites but they add a modulation ring for flux modulation reduction. They also redesigned their top plates they called Symetrical Field Geometry. At this point their problem was solved with even lower distortion ratings than their previous Alnico config.
I think that using Alnico is just a marketing buzzword now since they don't have any advantages left considering the inexpensive solutions available. If shielding is a must Neodynium can be considered as their price is going down.

Luke
 
#15
Ap said:

For referrence Fostex alnico drivera are about double the cost of standard.
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Okay, but that is after the markup.

Let me try it this way. How much would a typical 40 ounce magnet for a 10 inch speaker cost if it was made of standard ferrite?

Now, how much would the magnetic strength equivalent of that 40 ounce ferrite magnet cost if the magnet is Alnico? Notice I am not saying 40 ounces of Alnico, just as much Alnico as it takes to give the equivalent of 40 ounces of standard speaker strength ferrite.
 
#16
amo said:
An externally hosted image should be here but it was not working when we last tested it.


I was admiring this sexy driver from Davis Acustics on the PE site today, when I realized that I really do not know what are the benefits of using Alnico drivers. Can someone please comment on this? Are they usefull in open baffle or dipole applications? Are they worth it if you are going to limit their bandwith in a 3 or 4 way system? If you are driving them directly from an amp?

Thanks!
Click to expand...

are these available in canada ?

Who sells them?
WHat is the web-page..
 
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