I'm inclined to agree with bowtie's analysis. But that doesn't shed any light on who originally made them, alas.
I'd add that the holes appear to show different colored layers, which means plywood, which in turn, suggests an early date. I don't know exactly when particle board became the standard enclosure material - I assume mid 60s - and I know that many DIYers and high end makers favor plywood for better acoustical properties, but the drivers in these, and the plywood suggest a 50s date to me.