Previous lessons learned from builds 1 and 2:
Allow more than 24” behind the AT screen if possible. 18” sub boxes are often 22” or 24” inches deep and it cuts it too close for comfort. I wired my speakon inputs on the side of the sub cabinets just in case, but 4-6 inches of extra depth would have been nice. Sand is heavy, but it is a worthwhile endeavor to get a solid base below your bass. 2x8s for the main cavity lumber seemed like a good height. If you are doing two steps, use cheap 2x4s for the bottom one. Why two layers of 3/4” plywood/OSB on top of the sandbox framing? Because
says so. Trust his experience and don't be stubborn. Plus, 1.5” of OSB/plywood makes for easy round-overs with a router. Leave a 1” gap around the entire sandbox perimeter so that it does not touch the wall. Sound dampening/isolation is the whole point of the sand. Don’t degrade that by rattling your walls and the china cabinet upstairs.
The height depends on your needs and the best angle to see over the first row of chairs while being able to view the bottom of the screen. I went with 2x10 with 1.5” of decking on top.
Add power outlets in places where you might need them in the future. Maybe you will want near field subwoofers behind the second row of chairs. Maybe you will want to have power for an iPad charger near each chair. You can hide outlets with black faceplates, but it’s very hard to add them after the fact. Really hard. Pink fluffy insulation is cheap. Line the empty cavities with it so that your riser doesn’t become a resonant drum, even if you are on thick carpet. If you want an LED or incandescent rope light lining the underlip of the riser, plan ahead for that. I couldn’t extend my lip after the fact and needed to black rope light channel strips to hide the bulbs. The channels disappear in low light and create a diffuse effect, but it would have been cleaner to have a proper lip to begin with.
An extra pair of hands can cut the work time down by 75%. I hired two guys off of Craigslist (the odd-jobs and gigs section) who were between construction jobs and paid them $15/hour. Best move ever. While it was my project and I was “in charge” - I made it clear that I wanted their suggestions and input, which definitely helped the project along. I had the vision, but they had the years of expertise and had a few tricks up their sleeves to make things go faster/better.
Accent lighting added a really great look to my room. I went with cheap 3” 50w halogen downlights ($14.99 each) and I’ll add in LED bulbs when they burn out. Buying them separately is oddly still much cheaper than starting off with LED housings. Some people go with 4” downlights - I liked the accent effect of the 3” bulbs; my tray ceiling was 10” so it seemed to be better balanced. It’s 1000x easier to add the accent lights when you’re building a tray ceiling. If you are doing it after the fact, just get the power up into the tray and then pull your Romex through. Don’t make the spacing between light holes too far or it is much hard to fish the wire through.
If your spouse allows it, painting the ceiling black has an enormous effect on the perceived contrast — night and day difference. I was tossing out my carpet so I didn’t care about the drips, but keep that in mind and carefully prep your space when you are painting on the ceiling. The blackest of the black paint still has some reflection so heed the advice that so many here give on making a wider screen frame made out of black crushed velvet. It is like a black hole for light and really makes a tremendous difference. Get MDF or cheap plywood and a stapler and you’re done in a few minutes. I used SyFabrics and loved the result. JoAnne Fabrics is probably fine too, but the price fluctuates too much and I just wanted it done.
Seriously, check out the DIY offerings from DIYsoundgroup and GSG Audio. Premium components and the only catch is that some assembly is required! Flat packs from them, and from Parts-Express are the best investment you will ever make. Pre-drill your holes for mounting woofers. Put your hand between the woofer and the screwdriver or you will be buying a new woofer when it slips (mine did, and I was being careful). If using sealed enclosures, get speakon receptacles that are air-tight. Parts-Express.com has speakon connectors with different colors (blue, white, green, yellow, red) and it might help your sanity to color code your cables at the speaker end (ex. red for Fronts, yellow for subs) and then with the same color at your amp end if you are using.
Double the amount of time that you tell your spouse that you will be working. Things always take longer than expected. And, if possible, take a night off and just do something nice for her/him and say thank you for being patient. I initially failed and this and got some deserved backlash, but was able to make it right eventually.