You are correct about all the odd stuff with this cabinet. The cabinet dimensions are unusual. The grill cloth appears to be the 1st style diagonal pattern (similar to early Traynor cloth). The large back panel is separate from the rest of the cabinet.....must be fastened from the interior. Also note this panel has rounded corners at the top. The small back panel looks like a modification....note that the tolex does not appear to wrap that panel. Looking at the front, the top of the cabinet has an extension on the face, while the sides and bottom of the cabinet do not have this. The angled bottom edge of the cabinet is odd, as is, what appears to be, a port at the bottom edge. The horizontal port between the speakers is familiar, but it lacks the angled interior panels that typically form the horn. And the speakers are front-loaded into the cabinet .....but this makes sense as the rear panel must be fastened from the interior.
So, was this a one-off prototype? Was this an in-house experiment at Sunn. Or possibly something built by a Sunn employee as a personal project? I doubt that this is a complete modification of a standard Sunn cabinet. due to the odd outside dimensions.
The rest of my Sunn brothers weigh in!
