Consider heavyweight wardrobe boxes from U-Haul. Agree w using rigid foam but want to add a couple of caveats:
1. Reinforce the corners before you put in the foam sheets.
2. Make sure that the speaker and the foam CANNOT MOVE AT ALL inside the box.
3. Place the speaker in a sealed plastic bag or wrap w shrink wrap before putting in the foam sheets.
4. Peanuts are useless for heavy, dense items like speakers.
5. Remember that if they go UPS or Fedex Ground, they should be packed to survive a 6' fall onto concrete.
6. If possible, strap to a pallet and send them freight.
1. Reinforce the corners before you put in the foam sheets.
2. Make sure that the speaker and the foam CANNOT MOVE AT ALL inside the box.
3. Place the speaker in a sealed plastic bag or wrap w shrink wrap before putting in the foam sheets.
4. Peanuts are useless for heavy, dense items like speakers.
5. Remember that if they go UPS or Fedex Ground, they should be packed to survive a 6' fall onto concrete.
6. If possible, strap to a pallet and send them freight.