Here is how this dual resonator combo works:

The first one is “impedance-matched” to the open air or whatever is surrounding the absorber – this provides a convenient route for sound waves to pass through. The second resonator is there to cancel out any scattered noise produced by the first, and it’s this combination that achieves the 99.7 percent absorption level, no matter what the volume of the noise.

And below is a cool video about a sound proof room.  Most say it would drive a normal person batty but the ever brave Veritasium had this to say:

Is 45 minutes really the longest anyone can stay in a perfectly silent, pitch-black room?

I was not surprised to find that I could stay in there for as long as I liked and feel perfectly fine.

We hope you enjoy the video.

thanks to sciencealert.com for the great info

thanks to applied physics letters for the great info

thanks to the us navy/wikimedia for the pic