ebay dreamers...

That looks very much like one of the old Fern Audio cabs that powered the Musicbox in Manchester for many years, from what I remember they originally had Beyma drivers and sounded ok until the usual happened and the system had a long lingering death of loosing drivers, some replace by what was around, some not replaced. All sat letterbox hence the HF slot that way, All run from a hernia (is that the collective noun?) of dusty Amcrons.

I'm sure there's and engineer or five that worked in that sweat box on here somewhere to correct me....