At the time the BBC engineers were very ingenious in creating the LS3/5A. It is a fundamentally good piece of engineering and creative thinking, which is why it still exists in many clones. All good.
But many new technologies have come along since then. A new favourite in high end speakers is aluminium, as regularly used by Piega, Magico, Wilson Benesch and others, with odd examples in the ranges of a few others. Added to that is now carbon fibre, as in Wilson Benesch who use a hybrid alu/CF enclosure.
I'm in the process of making aluminium speaker cabinets out of commonly available 150x150mm aluminium box section, which can be any height you want for stand mount or floor standing. It can be reinforced with added aluminium sheets to create more thickness e.g. on the front panel. The 2 things you nave to deal with are...
- How to cut large holes for driver units if you DIY. Hole saws in larger sizes have too much friction, and you probably need a jigsaw.
- How to damp the panels. I've just posted another thread about this with some details from Piega - please respond!