Klipsch Heresy Speakers circa 1976...Cabinet wood question.

Cabinets... they  look like they are made of plywood but when I called Klipsch they were not sure, but  said that they may be   made of MDF material.
The back says ....TYPE MDBR.  Serial # 25P287.  
Are they made of wood or MDF ?  Opinions please
Never owned a pair but memory serves me as a kid back then visiting the local shop they were real wood laminated veneered plywood.
This may sound idiotic, but was MDF even invented or in use in 1976?
MDF came much later. Chip board was used a lot with vinyl wrap on lower priced cabinets and better cabinets used particle board with wood veneers like say JBLs of that era. A lot of manufactures with particle board boxes did use plywood for the front baffle as well. No doubt cabinets are made much better today with materials and bracing. Pretty sure the older Klipsch were plywood though and nothing wrong with that.

Quick Google search shows MDF was developed in the 1960’s. Be curious to know when speaker builders started using it. Possibly  MDF came later when they started doing more internal bracing. My guess it was B&W, only because that was the first company I recall advertising the importance of bracing in their cabinets.
Mine were plywood.  You can pull a driver to see the unfinished edges.  The commercial version may have been chipboard.  Those were always textured black finish if I recall???
My Klipsch Heresy circa 1980 speakers came in unfinished birch plywood - the cheapest version.  You should be able to tell from the back of the speaker.  There was no MDF option available back then.
I never owned the heresy,but the Khorns and Cornwall’s,I had from that era we’re definitely plywood and no mdf.

My vintage Heresy's are unfinished birch plywood. And I've had Altec Seville's that were also made of plywood. Same for my Rogers LS3/5A's.