Maybe it just me being a little (well a lot ) deaf, but I dont find my machines to be noisy enough to require ear plugs or head gear even on my Kubota RTV 900 which folks complain about being noisy. I dont see it. MY B26 has a loud transmission whine but not so loud that I would need to were hearing protection. And inside the cab on my LS it is super quiet. Sure I can hear the engine noise but it isnt loud and the vertical exhaust it at the top of the cab, but who wants to be totally isolated from any sound. One needs to hear the machinery "talking " to you when in operation so you can tell when something changes for the worse.
As for additional sound proofing, maybe some deadening under the cab mounting brackets or under the floor might help if you think the noise is too loud, but that would be about it. Most of the sound is going to be transmitted thru the glass which it 66% of the cab (all except for top and floor is glass).
If I wanted to further reduce cab noise, I would put a thick foam rubber floor mat in like the kind you put down to stand on around a work station. It think it would help in blocking any transmitted noise from the engine and frame a bit but that is about the only place you could do anything. I dont think you could achieve much from the top as it has a bunch of control cable etc under that that you couldnt do much anyway and most sound is not going to come radiating from the top. Only sound coming from below would hit the top and echo back, eliminate the floor noise and nothing would be bouncing downward anyway. My cab has a thick foam pad over my head so not much noise coming thu that except for the stereo speakers when I happen to turn on the radio.
If I ever get industrious, I may buy some of those interlocking foam pads and take out the rubber mat, use it as a pattern and cut out a total foam insert, then put my rubber pad back on top. There is some opening around the brakes and clutch that might could be closed up a bit for dust control.
