I am still building. What I figured out is that it is very much about the cabinet volume and not what dimensions you use to get there. Unless you are skilled enough to build or want to spend thousands on really complicated cabinets.
The 12" golds work best apparently in cabs of 90 to 205 litres. WxHxD x .61 or convert cubic inches to litres on line. Mine ended up an interior size of approx 125 litres after calculating in driver and bracing. 38" T x 16 x 13.75. 1" Baltic Birch. This is apparently a favourable size.
I am now going through porting and tunning. I am lucky enough to have professional help with this stage of the build. Correctly tuned, this cabinet should get me down to about 33hz which is very good.
I did not mitre I used but joints and re veneered the tops and bottoms to cover the end grain. My finished product will resemble the DeVore Fidelity Orangutan 0/96
https://www.google.com/search?q=arangutan+speakers&oq=arangutan+speakers&aqs=chrome..69i57j0...:
This is a fairly simple design to build. I have not built Cabinets before but do have solid basic wood working skills.
I would be happy to answer any questions you have about my process or tricks I learned along the way. I have never actually heard Tannoys so am really looking forward to it. I will post my impressions when I get there.
Cheers. Paul