Hello Lads,
I had posted before on Altec 515B cabinets, but since then I have changed directions, as I came into a pristine pair of Altec 416B woofers, and have decided on building a pair of full size Onken cabinets for them with my 288C drivers with the German Jabo conical horns sitting on top.

I am contracting with a cabinet maker to acquire the wood and do the cuts, as I do not have a table sayw that can do the precision cuts needed for a tight build, and his big shop saws can do. He will also cut out the speaker hole and drill all the screw holes for me. I will end up with a "kit" that I can assemble in my garage.

I need to make final decisions on the build before wood hits saw.
He can get 13 ply Baltic Birch plywood in a high quality form. I can order 3/4" or one inch thick sheets, The problem is that one inch sheets adds $40.00 per sheet over the 3/4" That's $240.00 extra to the total cost of the six sheets needed for a pair of cabinets.

So the question is, IS 3/4" adequate? or does one need to stick to the Hiagra 25mm or 1" thick sheet stock? is the 1/4" extra going to make that much more difference in the end?

Next is insulation. Following the Hiagra build, it appears he is using lambs wool felt applied only on the back and upper 3/4's of the sides of the baffles.
I see from Onken build sites on the web, that many new builds are using a full insulation with an additional back insulation of what appears to be audio grade foam sheet. except on the ports of course

And lastly, does the Onken box box sound best flat on the floor, on a plinth or riser, or even casters? My house has wood floors with area rugs, and my current floor speakers are the Sansui big 5500 the large mid horn filled version. These are on a 3 inch plinth and produce a very good full bass even on the bare floor.

Any Onken builders or speaker experts in the crowd, I could use some input on these questions before I start writing checks.
Thank you,
Donald Bowman