Why not horns?

Unsound imaging issues? Never experienced any weakness in horn based systems to image. If well designed as any loudspeaker should be, horns image wonderfully and can be used in near field if designed for as many of the pro monitors are. I design many for professional use most of the music today is monitored with horns just to bad they record much of it so hot today. This is not the fault of horns. Many of the professionals I deal with engineers scientists medical material researches etc could have loudspeakers of most any design but horns are the better choice for many of them. For audiophiles only a few buy horn systems though I try. They opted for more conventional design. Mostly out of fear since horns have such a greatly undeserved poor reputation.

loudspeakers transfer energy within the medium[air], does not transfer mass

Check out this link http://www.ndt-ed.org/EducationResources/CommunityCollege/Ultrasonics/Physics/wavepropagation.htm

JohnK, I might be mistaken, but I thought horns were used more to monitor pop recordings and typical dynamic speakers were preferred for classical recordings.

O.K. you guys- Springsteen's gone - get those wimpy horns out of here and bring in the typical dynamic speakers - we've got a string quartet to record in less than 2 hours.