A rectangular horn without any slots through the ends (i.e., the horn is either unslotted or only slotted through the thickness). If the horn is slotted then the width dimension (the side of the horn) is usually substantially greater than the thickness dimension (the end of the horn). Bar horns are often designed for gain by making the front thickness smaller than the back thickness.
The dimensions of a bar horn are specified in the following order:
Example: a 75 mm x 15 mm x 40 mm bar horn has a face width of 75 mm, a face thickness of 15 mm and a back thickness of 40 mm.