How to pack speakers w/out original boxes?

Help! I need advice on how to pack speakers,[Dahlquist 9c's], that don't have their original boxes. Speaker dimensions, Height: 23in., Width: 15in., Depth.: 12in.. Does anyone sell boxes big enough to ship these? They weigh 55lbs. each. What other packing materials should I use to protect them? Thank you in advance for your experienced Audiogoner wisdom! I'll take any advice that you all can give me.

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.
You've had some good suggestions so far. I've used structural foam from a store like Home Depot or Lowes. Get the good stuff, not the white, brittle stuff. Once you find decent boxes, use at least 1.5-3 inches of structural foam on all sides, top and bottom. Get a couple of different thicknesses, if necessary, to add up to the width you need. Use a drywall T for marking and as a straight edge for cutting the foam with a utility knife. Make sure the wrapped speakers fit tightly in the foamed boxes so there is ZERO movement. This will eliminate breakdown of the foam and possible abrasions. Clean the speaker with a damp cloth, then dry, before wrapping the speaker with stretch plastic kitchen wrap. Stretch the plastic wrap tightly around all sides, top and bottom of the speakers. The plastic wrap will eliminate any abrasions.

I've shipped a few different speakers and audio components this way and the packaging I created was WAY better than most factory packaging I've seen.
Being fairly paranoid about shipping, when I sold an amplifier to someone in Thailand. I double boxed it with foam between the boxes but went beyond that and used construction adhesive to bond 1/8" plywood inside each of the four surfaces of the outer box. That worked well both to make the box more rigid and, theoretically, to prevent something from penetrating the cardboard and foam, like the toe of a delivery driver's boot, for instance.
I agree with the foam insulation from Home Depot recommendation. I used 2" thick (4' x 8' board) and wrapped the foam covered speakers with cardboard that came with my plasma TV. Lots and lots of 2" packing tape.

I sent my speakers cross country and the receiver raved about the job and speakers were fine.
We ship aerospace parts. No matter what box you use buy four of them. Cut two of the boxes up and line the assembled boxes with the cut up cardboard pieces. You will in essence be building a double walled box. Much better and stronger. Double tape all the sides/corners of the assembled boxes on the outside.
Using the methods noted above, you should be in good shape.
Good luck, John
Thank you for all of your great advice. I really appreciate it. I feel much more confident, that my speakers will arrive safely at their destination. Thanks again.

Forgot to mention re0infrcing the corners. Sfar's method sounds like it should do the trick; for very heavy items, perhaps use 1/4" plywood.
I'd recommend a piece of plywood in the bottom of the carton, and perhaps attaching it to the speaker underneath with screws. That's what I'm thinking anyway. Further.. build a mini-pallet for each which will force the shipper to use a hand truck. Please comment on any downside to this idea.
"How to pack speakers without the original boxes?"
Very good advice here and just wanted to add....I use the heavy duty extra large trash bags to wrap speakers in to keep them clean from the styrofoam debris.
Use the 2 and/or 4 inch round foam noodles especially in each corner. They are usually sold in 4 foot lengths, and can be cut to size across or in half lenghtwise. Use them and double box even if you have the original boxes.
Whatever you do, don't let the UPS store package anything of value for you. They completely destroyed a pair of PBN speakers that they packed for me a few years ago. I usually don't have problems with shipping claims, but that time it was a real bear to get them to pay up.

They used a single outer box (no inner) with popcorn packing material for an 90 lb. speaker. That's it. No end caps, no hard or soft foam. Just popcorn.

If you know how to pack, you can make boxes stronger than the originals. It takes a little time, but you can use thicker and better foam sheets, cut round foam noodles for the corners and line the second box with protection also. I always keep the original boxes for everything, but I also add protection to the inside box and use an outer box on top of that. Pass on or split the shipping with the buyer. Better safe than sorry.
01-02-13: Shakeydeal
Whatever you do, don't let the UPS store package anything of value for you.

I agree 100%.
Find some hardboard corners are used for shipping pallets, these are up to 5 feet long and go around each corner about 3 inches and are about 1/8 inch thick. Incredibly strong and fairly light as well, can be cut with tin snips or a hack saw. Perfect for shipping speakers - use on outer corners of box and strap or tape in place. If box is dropped these will absorb the majority of the damage.