Horns are very good at directing sound and have high efficiencies. Horns are usually mounted under the dash. By doing this, difference in distance from left and right speakers are greatly reduced over conventional mounting locations. Since horns play mids and highs, tweeters are not needed. Even though horns are mounted under the dash, they give great imaging.
Horns cost more than conventional speakers and require customization.
In many installations a good equalizer is required to compensate for their high sensitivity. Left and right channels have to be summed up. The volume level of the center channel should be lower than the other speakers, since it is only supposed to make subtle changes to the total sound image. The best place to mount speakers in the front, in custom kick panels. By doing this, the path between the speakers and ears is minimized giving the best possible sound without having to add time delay circuitry.