How do pack a pair of large speakers

Use a moving companies shipping section. I've used Day and Ross a few time to move larger heavy speakers with no issues. They come to my house, wrap them up in padding and protection put them on a pallet and take them away, delivered to the other end's door. never had an issue, actualy easier then smaller items that i have to lug to the post office/etc.  

UPS has pack and ship as an optional service at SOME, not all locations. Give them the weight and dimensions, destination, they give you an estimate.

You drop them off unpackaged, they give you a final price, a bit more, a bit less ... They are responsible for packing and delivering, and the deal is done in your name.

I have used it to buy when a seller says ’local pickup only’, even bought from Canada, had shipped here. Tricky but it all worked out. Just need to have them drop them off unpackaged at the UPS location with Pack and Ship nearest them

IF you are selling, give the weight/size info to the buyer, let them make the deal with UPS in their name, you just drop them off. You can find specs online.

Carefully.

strong outer protection (box) speakers are secured inside the box with thick surrounding ( of bubble wrap..) Themocol/sponge spacers (3-6" thick) which keeps object in place no matter what. securing Corners are very important. Plastic cover to take shower. Imagine what abuse box is going to get during transport. Handlers not aware of how fragile, sensitive or expensive is product inside. Handlers may throw from 15feet high. Box may sit exposed to all elements. Forklift may brush the carton.

I recently moved and had the moving company do "custom crates" for heavy, expensive monitors. Turns out they charged $300 bucks for it and all it was was a guy taping some cardboard he cut on the fly to the speakers. Fortunately they weren't damaged and I got my money back but definitely go with original packaging or pay service that does this and only this.