Acoustic panels are used to make the room sound better by reducing or eliminating reflections and excess energy that muddy and smear what you are listening to. They aren't for soundproofing that's something entirely different. You'd use these in a home theater or music room to improve the experience.
As the car guys say: "There's no replacement for displacement!"
Thin panels only work on higher frequency sound and don't even put a dent in the real problems that exist in all small to midsized rooms. These are 51/2" (140MM) thick and are made to be spaced off the wall by that same amount. That gap between the panel and the wall makes the panel more effective, especially for lower frequency sound.
The interesting part of this build is how I fastened the cloth using the grooves and splines. I didn't want to use a billion staples to attach the cloth to separate frames and then try to figure out how to attach the frames to the boxes to make it all look neat. The splines worked perfectly and greatly simplified the process.

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