Let's mention the two camps:
electromagnets VS permanent magnets.
Permanent magnets: field strength tops off at 2 Teslas, REGARDLESS magnet material (Fe, Neo, AlNiCo - ANY of these will get you a 2T driver).
Want more? You need an electromagnet!
How strong can that be? Mighty hard to make one significantly greater than 2T on a comprehensible budget, yet today technology tops off at 10T(!!!) althought there's only one magnet like that, and it's used in the large hardon collider at CERN (building a driver with such magnet would get you in the budget of about 100 million dollars, making today's million dollar ultra-boutique speakers little more than a weak laugh).
However 1 thing Zupa clear: future is NOT NEODYMIUM drivers.
FUTURE IS FIELD COIL We just need to make it smaller and more affordable. (Yeah, and find a room temperature superconductor first! Cheers ;)
Opening credits:
Current densities of 100.000 A/mm2 to 600.000 A/mm2 are feasible in the temperature range of 4 K to 20 K (-269 degrees Celsius to -253 degrees Celsius) compared to 35 A/mm2 in state-of-the-art copper motor coils at room-temperature.
https://phys.org/news/2020-12-revolut...