Summary

So this thing has been on my mind for a long time and I finally pulled the trigger and built it.

I should say up front there are a couple issues you might want to solve before you start building this project - the led holders scale is a tiny bit off for the particular leds I used, this is not a huge problem but you aren't getting the maximum light out of a couple leds. It is really hard to line everything up - maybe use a slow curing glue? I didn't put in cutouts for power or for connecting to the arduino (perhaps one in the same) - you should think about this :) (i ended up drilling a little hole in the back of the box for a cable, not as pretty as i would have liked.

Arduino code, I did a slight modification of this code to remove the pot. I also found that the 'full' version didn't run very fast on my nano, your mileage may vary - https://learn.sparkfun.com/tutorials/interactive-led-music-visualizer/all

Ingredients -
Cuts on 3x 12"x6" 3mm Birch Plywood
LED holders (3D print) are not required but they make LED alignment easier
1 arduino nano (or similar size unit, an uno won't fit in this box)
1 adjustible gain microphone - something like this - https://www.adafruit.com/product/1063
RGB LED strip - this project uses 16 leds (sorry, not positive how to spec this, its the tight spacing version)
16x 1"x1" acrylic pieces 6mm thick (1/4")

Good luck!