To improve acoustics we attached a thick felt carpet pad, that also had a rubber backing, to the inside of the enclosure door. Felt is great at absorbing sound energy, and the change of densities between the felt, rubber, and wood door also help reduce sound transfer. I knew what kind of door backing we wanted and it turned out a carpet pad was the least expensive way to buy bulk felt.
The door of course will work in concert with the rest of the enclosure which is lined with batt insulation. We want this to be a pleasant bedroom so minimizing HVAC noise is critical.
Kelly also got some painting done tonight on the doors while I fussed with the above door installation.
We are slooooowly getting back into renovating and finishing the house. : )