Sverre,
Answering Brian and Ivan's questions would def. help a lot. There are some speakers that might even be able to do this (or come damn close) within a somewhat broad freq. range not just one frequency. Maybe not "full-range" at that level but some that come to mind are the Community Leviathan II, Community R6-51, Community RSH462, some EAW KF Series (i.e KF910F, KF920) etc.
These are "sky's the limit" devices, large, rightfully expensive and as far from the "average" speaker as one could imagine.
If full-range or "broad-range" isn't a concern, heck there's a good deal of horns out there ...
ScottH