I have long been curious about Altec's move in the early 70's from welded magnetic structures to non-welded structures in loudspeakers using alnico magnets.

Recently, i discovered this footage of Elvis from 1970 at the Culver City studio(three A4's for playback) . He's singing into the Satan of microphones, the EV 666. Watch carefully early in the video, he gets a hellish shock on the nose from it, even makes a comment to the boys in the booth.



This led me to do some research on the Electrovoice 666 family of mics. In the sales slicks they tout as a selling point a "non-welded magnetic return structure".

It now occurs to me that the "new and improved cast steel return pots" that Altec advertised for the newly introduced 416B/802G drivers didn't contain any new design features or characteristics that made them particularly special. It seems more likely that the sole improvement was the elimination of welds in the magnetic circuit.

My guess is that the welding process creates irregularities in the grain structure of the alloy that cause a discontinuity in the magnetic flow through the structure.

Can anyone expand on this or offer a more accurate explanation?