OK, I watched it -- bottom line for those who do not have time to watch -- they took decibel readings of a cheap generator and then put slanted sheets of plywood or sheetrock around the generator to deflect the sound down toward the ground. The slanted plywood left a lot of air circulation around the generator.
The decibel reading dropped by 10 decibels -- supposedly four times quieter, but I have no idea if dropping it by ten decibels really cuts the noise by a factor of four. (Is the decibel scale logarithmic?)
I may try the slanted plywood trick on my generator, just to see if I can hear a difference at all. Plywood is cheap and is easy to transport. I'm a skeptic, as you can tell.
Or slanted rubber foam mats?? I doubt they have the mass and composition to cause any meaningful deflection.
