My thought is trains wil only be pulling in and out at slow speed. I have L girder with cut out roadbed and my yard is plywood only a little wider than the 4 tracks. So I don’t think it needs sound insulation. I use the pressed cloth type carpet padding under all other tracks. Track is Gargraves. Will I regret having the track directly on the plywood in the yard? It will eventually be ballasted and ground cover.
From my experience any track that does not have some kind of insulation under it will transmit sound even if no trains are on that particular section of track. I personally would insulate it.
Well, real trains aren’t that noisy, I’d use the sound deadening material. I like the sponge padding used under pre-fab wood floors, it’s less than 1/4" thick but works very well.
Why not run a quick test in an isolated area of the yard and determine for yourself whether it’s too loud or not? Try it with nothing, then add the carpet if need be, etc…
Hey V8: In my humble opinion, you will be sorry. I have Gargraves track with Ross switches. Every inch is over cork roadbed. Even so, it’s still noisey. Me likes the noise, trains are noisey. Makes it more realistic. The roadbed raises up the track a bit so you can landscape and ballast. Go for it! later.