I really thought you had a better understanding of science than this. Alnico can be cast into shapes, unlike neodymium, and it has a higher flux density than steel magnets. Alnico also retains its magnetism under higher temperatures than other magnets, making it better suited for some applications. Alnico use in audio products looks like pure nostalgia, like tube amps and vinyl. I don't know much about microphone design, so perhaps the ability to make castings is somehow an advantage, but it looks suspicious. For speaker magnets, neodymium is an audiophile's best friend.
I'm not saying the AlNiCo is the only thing that makes the difference in speakers but aside from those, it was used in guitar pickups, not microphones. In speakers, some have designed them to use either a ceramic or AlNiCo with no other modifications and the sound IS different. As I originally wrote, whether it's actually 'better' is up to the user.
These aren't audiophile applications that I'm referring to, but differences can be heard. The AlNiCo is slugs, like many other magnets and I would think that part of the difference IS in the shape of the magnet since the ferrite is usually more of a donut and is outside of the voice coil, unlike the AlNiCo.
IMO, I would guess that the different shape/dimensions of the magnets matters more than the material (taller slug vs thin donut), but I haven't seen any data on the fields vs flux in the gap. Most guitar speakers aren't able to move far and they don't need to. I would like to see Salk's explanation for why he chose this.
