I really liked Dan Chen’s Instructable Ex Machina Sound Reactive LED Wall. It was so easy to follow, and the results were great. I created a temporary version using cardboard and vellum, as you can see in the image with the red LED lights in the middle – note the Arduino and breadboard hanging off the side!
The temporary version was great, but I wanted to create a more permanent version I’ve simply taken Dan’s idea (along with his Arduino code) and created a sound reactive light box. The design are simple translucent bars, created by a laser cutter to allow light to penetrate from the box. Check out the full build instructions at my Instructables page.