I recently built some light and sound absorbers, and thought I'd add my experience to this thread.
The house I'm renting has a living room with beige walls, and I've installed a ceiling mounted JVC RS4910 and a Seymour AV retractable AT screen. The image quality is stunning, but I knew the contrast was suffering on high APL scenes. My goal was to fix the most egregious area, which is a large section of bare wall near the screen. Since I can't paint the walls, and I didn't want to just drape velvet over them, I thought I'd kill two birds and build some DIY sound treatment panels and wrap them in velvet.
Since computer graphics is my jam, I thought I'd get a rough idea of the impact these panels would make by doing before and after simulations using raytracing. So I modeled my living room and did a comparison.
(NOTE: these two images are computer graphics
! Don't be fooled, like the other folks I've showed these to
The difference in the light hitting the "black" areas of the screen is pretty plain to see, without resorting to subtracting the second image from the first. This is meant to be representational, and not 100% scientific. To get it just right, I'd need to more accurately determine the material properties of both the screen and the wall. But regardless, it was enough to convince me that it would be worth the effort.
It took pretty much a whole weekend to construct the panels, cover them in velvet, and hang them. The panels are basically Roxul stuffed inside 1x4" furring strip frames, and held in with twine and black plastic. Here are some photos of one of the larger panels.
Front side, before being wrapped in velvet:
Back side, before being covered in plastic:
Back side, after being covered in plastic, and with hanger hardware attached. I future proofed them by adding hangers for both portrait and landscape orientations.
I then wrapped all three panels with Syfabrics black velvet, which as others have pointed out, is identical to Joann Royalty 3 (which I used on a previous project). Using steel wire, I was able to hang them all in series from a couple of hooks in an exposed ceiling joist above the wall. They don't quite sit flush on the wall, but close enough.
Here's the actual wall before:
...and with the panels in place:
This location is the sweet spot for being near the screen, and also roughly hitting the first reflection point from the speakers to the MLP.
And the obligatory screen shot, where you can see the panels working hard eating up light on the right side:
The room is still nowhere near being a bat cave, but these panels made a noticeable difference to overall contrast, especially for scenes of around 50% APL. I'm really happy with that outcome, and while I'm calling it done for this room, I'll certainly be carrying on the theme (to more extremes I hope!) in my next room.