It doesn't get any simpler than this: simple, organized and precisely drilled holes for sound resonance and absorption.
The names explained
The names are references for the spacing and hole diameter.
For example, in the BA16-6A:
"BA" stands for "basic"
"16" is the diameter of the holes in milimeters
"6" is the spacing between holes in milimeters
"A" means that the holes are placed horizontally
Note: if the end letter is an "U", it means the holes are placed diagonally