Re: 60 Degree DIY Mid Hi
The double 21 is nothing fancy. It’s basically just two B&C designs joined together.
The trick is to keep the weight down. The B&C 152’s weight 40 lbs each!
To do that I am going to use 19mm ply and corner ports because they brace the walls without adding weight, plus some additional bracing on the back panel & walls.
For me, weight is more important than port turbulence, so the port design is not fancy. The box also has to be the appropriate size so it can be combined with our existing double subs and can it be used as a base for ourTurbosound Flex Array as well as the DIY.
I considered building a design like this http://www.dasaudio.com/en/p/ux-221-2/. It gives you a bit more efficiency, but the box weighs 130 Kgs.
I have the drivers in stock and hopefully I can start building soon 
