Most economical way to ship large speakers?

 I work in the shipping industry as a truck driver. I assure you that you will find some shipping options cheaper than others.  I can also assure you that the cheapest ones are most likely to destroy your freight. They will probably even give you a hard time when you file a damage claim. I would talk to some freight brokers at length, discussing not just shipping cost, but also insurance, willingness to honor a damage claim, reputation etc.  I myself will not offer my opinions on who to use. That would make too many people in my field unhappy. You want absolutely guaranteed damage free delivery? Rent a trailer or a small truck.