How to pack speakers w/out original boxes?

you can get heavyweight boxes from u-haul- their small wardrobe boxes will probably fill the bill. I would fully line them w rigid foam and wrap the speaker in both directions w large bubble wrap. Make sure that the speaker fits very snuggly, there should be NO room for the speaker to move. And take pictures. Or have UPS store or Kinko's package them to that they take responsibility for making sure it meets their packing requirements.

For packing material use swimming pool noodles. They are these hollow closed cell foam tubes about 4 feet long. Kids use them to help stay afloat. They are cheap in off-season if you can find them. Just cut them with a knife to the size you need.

Once you have the boxes, use ridged Styrofoam, and plenty of it on all sides, not anything soft. Snuggle is the way to go for it their is any movement in the box itself damage will result.