I think some other sound variables come into play such as are the train room walls closed in as in covered with sheet rock, is there a ceiling or just open rafters, height of the ceiling, bare floor or carpet, etc.
My last layout was 6 X 15 located in a finished 14 X 18 1/2 room with sheet rock ceiling (8 foot) and walls as well as indoor/outdoor type carpeting on the floor. I used Mianne benchwork with 3/4" plywood sheets covered by 1/2" Homasote. My Ross track was embedded in Ross Roadbed, attached to the Homasote using the Gargraves # 4 screws, then ballasted. When the trains were running, there was train noise such as wheel clicking over the track joints and the MTH locomotive sounds effects, but no "rolling thunder" which I've read the most complaints about over the years in terms of layout noise.
Here's a video I shot on the layout using my cell phone sitting on top of a PRR-style signal bridge. The sound in the video is what it was that night in the train room. I think the Homasote in combination with the foam Ross Roadbed helped to prevent the "rolling thunder" sound. I'm sure other brands of foam or even rubber roadbed would help in the same way if used with Homasote.
Incidentally, if I had the MTH locomotive sounds turned on, you had to raise your voice a little to speak to someone four feet away. Don't laugh, but I like to have the locomotive sounds on when running the trains.
