Quote Originally Posted by magnarc View Post
And there is now a two piece pair of 511A's. Mind you these appear to have been drilled for three bolt hole drivers too.

I've never seen 511A that were not 2 piece?

Altec drivers were 3 bolt originally, same pattern as JBL uses

Here is a field coil unit but early permanent mags were 3 bolt also.

I think the 2 piece horns were easier with the 2 bolt.