The best way to break in speakers.

I think if the loudness level is too low, the break-in period is unnecessarily extended. Consequently, I tend to to do break-in at levels somewhat louder than normal listening.

When I was working retail I'd always put each new floor model through the same workout.

I'd use a mono recording or take a Y splitter and feed a single source channel output into a stereo amp. Then I'd face the speakers towards each other and place them as close together as possible. I'd wire one speaker out of phase from the other.
Since both channels are not playing the exact same thing, they will cancel each other out pretty well. The point of this is to reduce the overall volume so that they aren't annoying while they are breaking in.

Then I'd put the source on repeat. Set the volume dial at about 20% louder than we would have it under normal listening conditions. And then let it run 24/7 for about a week.
Sometimes I would use special "break in" discs. But I found that, under these conditions, they really didn't work any better than regular dynamic music.
Kodo drummers was my favorite disc. LOTS of cone excursion combined with frequency extension. In other words, give them a good workout right from the start.

Anyone who says you have to take it easy on a speaker or do anything else special is giving you hogwash. IMO

There's a speaker and electronics break-in track on the XLO Test CD as
well as other Test CDs. The XLO track is put on repeat and allowed to play
fairly loudly for anywhere from a few days to a week or longer, depending
primarily on your tolerance for the racket on the burn in track. The speakers
can be placed directly facing each other to help things along. Blankets can
be placed over the speakers to reduce the noise.

Play them normally and enjoy. Test CDs might contain tracks that could damage speakers. Stereophile Test CD, for instance, contains track with high frequencies at 0dB that can fry tweeters if amp is set to normal listening levels.

Kijanki wrote,

"Play them normally and enjoy. Test CDs might contain tracks that could damage speakers. Stereophile Test CD, for instance, contains track with high frequencies at 0dB that can fry tweeters if amp is set to normal listening levels."

Maybe so. The break-in tracks on Test CDs, however, will not damage speakerst. It also helps to read the User Manual if you're, say, a newbie.