The insulation in our building is average, but the huge weak spot is the door to the hallway. I don't have a big problem with hearing people out there (although a bit of reduction would be nice).
The problem is that I love to sing along to my music, but am to embarrassed to do it knowing people could be out there listening or giggling.
I do plan on putting weatherstripping foam around the doorway, although that won't be close to enough to make me feel comfortable. I was considering a 4x8 panel of egg carton foam over the whole inside doorway. Would that reduce the sound substantially, mainly vocal frequencies?
There is a local place that sells foam but I think it would be really cheap and not made for acoustics.