box building

It's actually two questions. First, is bracing absolutely necessary? Everything in the build is sandwiched between the top and bottom and the subs will be mounted onto a double face. Secondly, when it comes to carpeting the box, is it better to cut out segments for each side or to wrap the box in one big piece of carpet? Thanks in advance.

It depends on the size of the box and the sound pressure levels it is going to to have to take. It's a good idea to brace the joints in high SPL setups. But if you use good glue and fasteners for standard applications it not absolutely necessary. I always use at least 3/4" MDF for 12" or above subs, and 5/8" MDF for smaller boxes. For long throw subs with a 1.5" excursion point to point (which is 3 inches total travel) bracing is a must! Its easier to use one large piece of carpet and double cut the seams by overlapping and cutting through both at the same time. If you don't have one large piece, cover the largest sides first then do the smaller sides last. Double cutting gets a consistent matching edge seam.

Idk if this helps but I have 2 Addictive Audio Version 3 12s. They are sharing a common port and each side will have 2.25 ft^3. The subs will be mounted onto a double face. <blockquote class="imgur-embed-pub" lang="en" data-id="a/V24AS"><a href="//imgur.com/V24AS"></a></blockquote><script async src="//s.imgur.com/min/embed.js" charset="utf-8"></script> This is the design and it's not to scale (obviously).

https://imgur.com/FsvCjNF

The SPL Specs are more telling than power handling per sub. Your subs are only .75" Excursion point to point (1.5" of total travel). Based on what I can see you should be fine if you don't brace the box. But in your design the angled braces should smooth out the air flow to the port. Use a good glue and plenty of fasteners and you will be good. If you were running some 12" Dual voice coil Cerwin Vega Strokers Dual Spider or the like which require 3.4ft^3 per sub and a 6" port per sub then you would definnitly need to brace the box seams.