How do you properly break-in a pair of speakers?

Just throw in a CD and let it go!

Various full scale music will work fine (classical with organ is good). I do not play new speakers loud @ first (if the sound becomes compressed or dry, then this is too loud, IMO, plus who wants to listen to this).

Most of the new speakers that I have owned loosened up in the first 100 hours (as far as increasing the volume goes), so try to be patient if you enjoy listening @ higher levels.

I don't know if a fairly high volume will actually damage the drivers in the beginning, but I try to treat them as I would a new automobile engine and this has worked well for me.

What speakers did you purchase? Could be that someone will be able to give you a time line based on experience.

Burra hit it right on the head. Just play a disc or run the tuner. When I was breaking in mine, I just let it play whether I was home or not. Not at high volumes. I only listen at moderate volumes anyway. The more you listen during the break in period, the more you will realize how much the sound is actually changing during the whole. Most manufacturers recommend to just play them normally.

Ryan's got it right. Even better is to boost the bass if you have tone controls (huh?). You'll soften those surrounds and spiders quicker....

While you are away from home run your tuner and tune for interstation hiss. This hiss contains all frequencies and will break in your loudspeakers lickity split. Of course, enjoy listening to music when you are at home.