I would checkout http://gr-research.com/diysubwooferkits.aspx

Danny is a great guy and his youtube channel is really informative.

Got the equipment yesterday, and so far, here is what I am doing with an old sub cabinet. If it does not work out, then I will just make the recommended cabinet for the new sub.

https://ibb.co/hV38HKg

Man, Do I! As expected, some systems come together better than others, regardless of the components involved. In this case, I found something very rare for my liking. The bass didn't just improve,>> it's the bass that I haven't heard for years. Just the right level and integration, and the use of a Velodyne SMS-1 provide the balance that I missed so much. To be clear, a Velodyne SMS-1 is a bass management system that measures the room using a mike and your sub, and then adjusts the EQ accordingly. At first, I was using the Velodyne just for the crossover to the main amp in my system. The reason for this is that the line level crossover in the GR Research amp lost one channel. I have no idea why and don't care, because using it means long runs of interconnects to and from. Ok, so as I stated, the music is quite moving now, not only in the bass, but above the crossover frequency of 70 hz. I have listened to numerous albums, mostly with surprise of the fact that there is the best bass to be had, and sometimes not. Point is really good recordings are overwhelming to me. That is because I haven't heard them 'correctly' in some time. You might wonder why I am using servo sub with DNA2 speakers. Simple really, in my room speaker placement isn't much of an option concerning the best placement for bass. Fortunately, the midrange on up is fantastic using the Mark Audio 12P drivers. They do pretty good bass, but are rather made for frequencies above say 80-100hz IMO. Since the DNA2 sound is fast to begin with, a servo sub was the best choice as it blends perfectly.

GS,

  Yes, it was shot in the dark for me with this cabinet, although I knew that the Cu Ft, I think around 1.8 was right in the ballpark to start with. The cabinet is beyond well braced, and I tried something unusual>>> The magnet of the bass driver was quite close to one of the braces for the opposite panel. I used a heavy bead of silicone to attach the magnet to the brace. Because of the shape of the brace, which is cut in a half circle, I was able to attach with silicone in two places on the magnet, one attachment on each edge of the magnet. I mention this because I have seen speaker designers use a similar technique in cabinet design, but with bolts. Anyway, the total outcome from this enclosure arrangement is quite beyond my expectations. I have toyed with the idea of using a subwoofer stand offered by Iso-acoustics, but doubt that I will try it. I couldn't possibly be more satisfied with the present arrangement. I do believe that the Velodyne SMS-1 helped out by it's measuring and correcting for what it can with the room.