Someone mentioned JBL, which kind of makes sense. I once built two cabs loaded with 15" Altecs based upon a JBL design that looked almost exactly like that.
EDIT: And by "once", I mean back in the mid-70's. The design was based on a pair of JBL 15" PA subs.
EDIT: And by "once", I mean back in the mid-70's. The design was based on a pair of JBL 15" PA subs.