Soundproofing Doors at Home Depot

Instead of trying to change your door, why don't you try deadening your hallway. Hang some decorative burlap on the walls. Get creative. If the hallway is big enough, a few plants might help out, too. Place a few rugs on the hallway floor. As it is, I have trouble with the idea of sound leaking out from under your doorway, especially the mids and highs. Of course, bass freq will go right through your walls.

Here are some suggestions in the order of being effective (and most likely the most costly first)
1. Change the door and frame to an outside door with a wooden threshold and insure there is good weather stripping.
2. Change the door to solid core, weather strip the entire door, add a threshold at the bottom and use one of the rubber gaskets on the bottom of the door to seal the bottom.
3. Change the door to a solid core door and weather strip,
4. Add layers of sound absorbing material to both sides of the door (this can be done to any, but will not have much benefit on solid core doors).

The other aspect to consider is that having mass and an airgap makes the best sound barrier. Studios use 2 doors with an air gap in between in critical areas. If you have a location or way of adding another door with an airgap (need only be 6 inches), you can make great strides.

Another approach could be to put a carpet runner in the hallway that extends under the door, and maybe a decorative textile hanging (with some thickness and weight to it, not a linen) on the listening room side of the door itself.