material for making the motor of a field coil loudspeaker

[arivel]

Hi everyone.
there are materials called soft magnetic and they are halfway between a permanent magnet and a ferromagnetic material.
I would like to try to make a field coil loudspeaker where the maximum amount of flux-density is very important but also the amount of current it takes to create the magnetic field.
there are materials like FeCo alloy (soft magnetic) that comfortably exceed 2T but I can't figure out how much current it takes.
if it takes much less current than a material such as the economic FeSi alloy, this would be very interesting, then the price must also be considered.
bye thank you

 

[onatirec]

Electromagnets are made of coils of wires. Magnetic field strength is proportional to both current and number of turns in series. 100 amps through one turn produces the same field strength as 1 amp through 100 turns - so it's not enough information to ask only about the current. The induced flux density is a function of the field strength; you can look up B-H curves of the steels you are trying to compare. You could look up e.g. hiperco or vacoflux vs silicon steel to get an idea of how the flux density changes for similar values of H.

 

[arivel]

I think there is a misunderstanding.
when I spoke of the current I was referring to something else .
use less current to have the same magnetic flux density (tesla) than another material

 

[IRstuff]

The go-to materials for speaker magnets used to AlNiCo, ferrite, and Neodymium. I've seen ads for speakers with other materials, but these 3 are it, and for cost, it's ferrite, and if not, then Neodymium.

https://blog.miscospeakers.com/magnet-materials-in-speakers

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[onatirec]

Op is asking about soft magnetic materials, ie electrical steel. Permanent magnets are hard magnets. Though it's not clear op understands this distinction, as ferromagnetic material can be either soft or hard - and silicon steel is already soft.

I will reiterate again, you need to look at BH curves to compare different materials. You can't just ask vaguely. There are many silicon steels and many cobalt steels. Better steels will absolutely be more expensive.

https://audioxpress.com/article/better-microspeakers-utilizing-hiperco-alloys

 

[Gr8blu]

arivel: The easiest material to magnetize is pure iron (Fe). However, it is also the loosest in terms of repeatability (hysteresis). As different materials are added to the mix, the level at which the combination saturates changes - sometimes higher, sometimes lower. The difference between the hysteresis slopes also varies. Proportions of specific materials can also affect what is going on - something with 1.3% silicon content has a reasonable excitation (current) requirement, compared to something with more silicon . . . but the overall saturation occurs earlier (i.e., a lower magnetic field strength).

Everything is a trade off. As onatirec noted, use the available B-H curves to determine which materials work best for your application - and which fall within your budget constraints.

Converting energy to motion for more than half a century

 

[arivel]

First of all, hello and thank you all for the replies.
I have no preferences on materials, as long as it is not a permanent magnet, now there are so many materials that did not exist until a few years ago that many, including me, ignored their existence. I am interested in a material to make an electromagnet that has the maximum flux density (higher than that of other materials) with the minimum electric current. therefore a material that can be the best alternative to materials commonly used for this purpose (field coil loudspeaker).
I mentioned the soft magnetics because I don't know them and I wanted to know from you if they have the characteristics I'm looking for.
hello onatirec it is not as easy as it may seem to find the BH curves
where do you recommend I look?

 

[onatirec]

Search around for Hiperco 50 or Supermendur. This material was invented in the 50's. Permendur has been around since the 30's, so I'm not entirely sure what you mean by materials that did not exist until a few years ago. I would think that anyone who designs electric motors would be aware of them; Carpenter and other manufacturers can be found at probably any large trade show. I suspect the drive towards smaller and more efficient electronics would increase the use of these materials.

It's indubitably good steel. I'm sure we would use it all the time if money was not a concern.

 

[arivel]

since in this forum there are smart people so I take the opportunity to ask other questions, if you want to answer them.
Is the material hiperco 50 workable on the lathe? does it rust?
if I put hiperco 50 in contact with other metals such as steel or relatively pure iron, does an oxidizing reaction take place at the point of contact in the long run?

 

[onatirec]

electrical steel is usually produced in thin laminations. What i can see on Carpenter, is that hiperco comes in .35mm and .15mm thickness. these are stacked into cores and welded or stitched together. we've turned down cores of silicon steel on a lathe here. you have to take light passes so it doesn't distort. i'm sure you could do the same with hiperco. I don't have any experience with it directly; we tend to use cheaper steels. I expect that it would rust... rust is an oxidizing reaction... not sure how the presence of another steel would have any effect.

 

[waross]

The speakers that I am familiar with use a very powerful permanent magnet.
The voice coils is most often copper wound on a non-magnetic form.
If you are replacing the permanent magnet with an electromagnet, greater diameter may be cheaper than exotic material.

Field strength within given dimensional restraints depends mostly on the gage of the winding wire.
If you double the number of turns, the resistance and the current are halved and the Amp turns remain the same.
BUT
Double the turns results in double the induction.
This may be a good thing as it will tend to smooth out unintentional variations in supply voltage.
This may be a bad thing as it will tend to retard intentional variations in supply voltage.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[arivel]

and instead , which is the material with the highest magnetic permeability ?

 

[arivel]

my idea is to use a full cylinder with hiperco 50 only for the central core wrapped in copper coils.
this, because hiperco is expensive and difficult to work mechanically, with it I can get the maximum magnetic saturation with less copper coils and less electric current. then instead use another material for the outer O-ring. I had thought of mu-metal because it is easily machined on the lathe, costs less and has a very high magnetic permeability, then I discovered that its magnetic saturation is very low. So my question is the following: which material can I use for the outer ring ?
maybe steel with low carbon content?. if I do this, however, I get a lower general magnetic saturation. Maybe it's better to use a material that has a lower magnetic saturation but greater permeability than hiperco? .
I await the correct answers from you.