Acoustic doors?

There are 2 types of sound transmission, air born and structure born. Air born can be stopped mostly by mass alone. Structure born requires decoupling, which means a mass layer, air gap (or other low density layer), followed by another mass layer. Recording studio doors have mass layers and an air gap. They are usually very thick (3" or better).

Albert pointed out doing 2 doors with a significant air gap. This is also done in studios and is called an air lock. It is a greater air gap and thus is even more effective.

Last, I'll point out that STCs often quoted for things like this are often useless. STC (sound transmission coefficient) is for 125 Hz. Usually the problem frequencies are much lower, like around 50 Hz and are structure born.

Now the door probably is the biggest problem you have, but there's no point in buying a very expensive studio door if your walls are single layer sheetrock and offer little sound isolation. Sound isolation works like the old addage "a chain is only as strong as it's weakest link."

Probably the first thing to do is determine what type of sound transmission is the problem and go from there.

Here's a linke to our resource page. There is an article we wrote on sound isolation that might be of help.
Rives Resource Page

Thank you all for your helpful respsonses and references. One of the aspects I love about this hobby (or profession for some) is the chance to apply science and test theories in solving problems. I now have some more food for thought, and for a temporary fix for my leaky door I will try hanging my 30 year old Coleman sleeping bag over the door. This will ad some mass and create a 5" air gap. I will post the effectiveness shortly.
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?

For a cost effective and functional solution to your problem, consider this: . . . . headphones. You'll get to hear some really good tunes, and your wife will be able to sleep.

I have headphones and use them when I can. However, there are a lot times when headphones are not an option.
In any case, I was able to tighten up the door tolerances and temporarily hang two cotton and one wool blanket over the door. I have achieved a considerable improvement in sound attenuation and the Mrs. is surprisingly impressed my blankey solution. It's kind of like entering the yurt when you squeeze through the blankets
I see installing a solid core 1 3/4 exterior door with the best weight to price ratio and imploying a good gasket along with stiff framing and hinges as the best solution so far. Then I can see where the next weakest link is. I can't wait.

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.