Acoustic doors?

To reduce sound transmission you need one or more air spaces, this reduces the path that sound can travel through.

First option is two or three solid core doors where you create an air gap between each. I don't know your room or construction of your space so I can't elaborate on how and where to hang them.

I had a hollow core door on the utility closet housing our central AC unit. I replaced it with a solid core plus a fiberglass panel on the back and it reduced the sound enormously.

Upgrading the second door to solid core, the hall way door between the utility closet and my listening room removed all noise competing with the music.

Sound works the other way around too. Stopping it from going through to the bedroom is the same approach. Gaskets may be required if you have much space under the door and unless the walls are filled with fiberglass sheets like I've done in my room, the door may no longer be the transmission path after upgrade.

Nsgarch I think we are agreeing and disagreeing.

I agree with your comment on mass and that's why I posted the comment about two doors. However, the space between them is some benefit too, especially if a sound panel is attached. (Hals_den said aesthetics were second to performance).

This from Wired Magazine

How Sound Travels

Let's look at sound, and think about how it travels in order to better understand how to stop it or contain it. Sound is made up of energized pressure waves in the air that cause objects in its path (including our eardrums) to vibrate --objects like walls, floors, doors and ceilings. (Deep bass energy is the worst, as you may have noticed when you walk past a dance club or when a car with a booming one-note subwoofer passes by your home.)

Adding loosely packed fiberglass insulation in the wall cavities of interior walls further reduces the energy passing through, in effect making the air between the walls more lossy. Staggering the wall studs (see below) on each side prevents the bass from passing through because it has to move the studs and the wall, which is very hard to do.

This from University of Massachusetts, Amherst, MA.

Sound attenuation batts soak up sound and can improve the STC rating of a wall. We carefully installed 3-1/2 inch thick sound attenuation batts (Owens Corning http://www.owenscorning.com/ 1-800-438-7465) in all stud cavities after the resilient channel was fastened to the wall. We purchased batts that were sized for steel studs. These larger batts extend into and completely fill the hollow profile of the steel studs. Language on the package claims they can improve partition STC ratings by up to 10 decibels.

http://www.owenscorning.com/quietzone/products/products3.asp

Specification from Owens Corning including specification of attenuation with acoustical batting and sealing.

I agree with your comment about solid core 1-3/4 doors. In fact that's what I used in my home and what I suggested in my post.

I also contend two are better than one and better still would be if they did not line up with each other, but rather were staggered. However this is likely not possible in a residence where we have to work with what we have rather than constructing from scratch.

Hals_den

For a more permanent fix, I'm thinking a heavy exterior door with good seals would be the most economical solution. Can anyone recommend some good manufacturers of such doors?

I don't know where you live, but if there's a Home Depot or Lowes nearby they sell several quality levels of solid core doors. I opted for plain (no panel) paint grade since the other interior doors are this style. You can go solid for as cheap as $75.00 or $80.00 (I just checked via internet).

Alternately, if you have a builder supply in your area, they stock door and window in an amazing array of styles and finishes, hopefully to suit your home and your wife :^).

Often a local handyman will have a wholesale account at one of these places, you can go shop with him and pay him a markup on the door and his labor and everyone comes out great. I did that with my three solid core doors (two different contractors) and got great results both times.