Jack -

Cardboard egg boxes can sometimes help make a decent recording studio, but they don't work very well for a space where the sound is mostly conversation/communication.

For a recording studio, practice room, or auditorium, the goal is to prevent the loud noises you intend to make there from getting out at sufficient levels to annoy the neighbors.

For an office space, the first goal is to not have noises loud enough inside to leak out.

There are, of course subsequent steps in getting the final result wanted in either case.

For a studio, you likely would also want to absorb the sound at the wall so it doesn't echo back and drive your mics crazy. For an office a small reflecting surface close to the person speaking can sometimes reflect back enough to improve the clarity of what both the speaker and a nearby listener hear, with the possibility of reducing the tendency of the hearing impaired to "speak louder." In the latter case, the "echo" must come back before there's enough lag to make it sound like it's not part of the original speaking.

Some home architects, and "decorators" actually have paid at least nominal attention to acoustics at ordinary sound levels, although it's hard to find enough info all in one place to put together many basic principles, or to know when to use which ones.

John