Since I'm interested in Altec I found out that there are two philosophies: The people who say bracing is important and the cabinet should sound "dead" and the people who say that the resonances are part of the speaker's conmstruction. The original 825 cabinets also had the thinner material, so I built up these. Of course I still have the chance to add another line of plywood to the ooutside walls.
But I'll do it step by step, since I'm just at the beginning of my journey. ;-)

I have the A5 for 1 1/3 years now. In the beginning they sounded pretty terrible, there were several room problems and I had to get to know the speaker, but now I'm at a point where it sounds pretty good. At this stage I really want to try something, that's why I'd like to know how to include a tweeter to my Hiraga 2 way crossover. Could someone help me please?

After trying that I want to do some "modifications" to the cabinet...

I found a picture of the speakers. Today they are placed slightly different and are more pointing to the listening place.