The disappearance of the traditional amplifier

Atmasphere, I asked this question over at AA and I'd be interested to hear your opinion:

I'm curious who believes that a FC motor is inherently superior to even the best AlNiCo magnets, and who, conversely, believes that there is no such inherent superiority, and the only advantage of the field coil is the ability to tune parameters with the coil voltage/current.

Hi Paulfolbrecht, I for one believe the FC technology to be generally superior, but like all other things in this sport, a lot relies on execution. So its dangerous to make generalizations on that account.

FWIW though, you can't really 'tune' the parameters once the motor is designed- if you have that ability, it means that the gap isn't saturated, and if the gap isn't saturated, the motor will not be performing very well, field coil or no.

Atmasphere,

If this is a sport, why have I gotten so fat?

What, you don't consider Sumo wrestling to be a sport?

I wasn't alive back then, but I think that field-coil speakers in the first part of the 20th century were actually significantly cheaper than permanent-magnet types of similar performance . . . they were NOT a "high end" design. This was an era when the labor and expertise for winding coils was cheap and plentiful -- even budget radios were chock full of inductors, chokes, and RF transformers that were typically wound in-house. On the other hand, high-permeability magnetic materials were VERY expensive or even unavailable - the infrastructure for securing the raw materials (especially cobalt) and making high-quality alnico alloys . . . this is all very high-capital-investment stuff.

The early Lansing alnico designs specified a flux in the magnetic gap of something like 13,000 gauss . . . I'm skeptical that any field-coil design of that era could even produce half of that. And as I understand it the move to ferrites in the 1970s was a reaction to geo-political events - the main deposits of cobalt in the world fell under the control of regimes sympathetic to the Soviets, and the price of alnico alloys shot through the roof in a very short time.

I am also quite skeptical of the claims for the superiority of ferrites vs. neo vs. alnico vs. field-coil arrangements . . . but all of these methods of making the magnetic flux allow very different approaches to the design of the motor structure itself, and this does have a huge, fundamental impact on the driver characteristics. The first generation of JBL professional drivers that used ferrites were very carefully designed to have the same magnetic characteristics as their alnico predecessors, and I've mixed and matched them in sound-reinforcement systems and couldn't tell a bit of difference (except for the odd alnico driver that's lost some of its flux).

But I will agree that the Alnico magnetic structures are so much more elegant in an engineering sense . . . with no stray field, and much easier on one's back when moving them around. And I can see some similar appeal to a modern field-coil speaker.