Though most interior doors are 1 3 8 inch thick exterior doors are typically 1 3 4 inch thick.
Sound insulation under door.
The thicker the door the better it reduces noise transfer.
Using curtains for soundproofing a door works in very much the same way as it does for insulating a door.
The key is to make sure that the fabric you use is thick and multilayered the more layers the better as this helps muffle sound waves you could even get a consider getting a specially made acoustic curtain.
You can actually go one step further than a solid core door and buy a sound blocking door.
Doors made specifically for blocking sound typically utilize 1 2 inch thick particle board sound board an interior layer of lead and integral interlocking thresholds and sweeps.
Just be aware that replacing a 1 inch door with a thicker one will involve some carpentry modifications to the door jambs.
Fill the gaps with a draft stopper either purchased or homemade.
Norsmic car sound deadening roller 0 7lb extremely smooth sound insulation roller metal noise deadening sound deading tool 1pc 1 69 inch by norsmic 9 99 9.
Maxtid under door draft stopper 32 to 38 inches grey adjustable insulation sound proof door air draft blocker for noise light smell stopper 4 0 out of 5 stars 4 749 19 99 19.
The thicker the door the better it reduces noise transfer.