I thinks horns should stay out of the car altogether. Horns,specifically for tweeter point of view, were designed to disperse wide and get loud. Wide dispersion + getting loud with horns is not a combo imo for cars. You'll get lots of radiating sound flying all over the place and really start to hear 3rd order distortion, especially if your dash is not very symmetrical. You never had a ringing sensation after listening to a horn setup in a car?
What about tonal issues? Things always sounded hollow and empty. No wonder beefy midbass's are required(drowning out that sensation lol). Another peeve is the lack of stage height and depth when using them. Maybe with some tuning you can fix the depth issue but requires way too much tuning.
To me the end results werent as satisfying compared to a decent tweeter that you can mount virtually anywhere due to the size of tweeters.
Dont even get me started on ribbon tweeters and planars. //content.invisioncic.com/y282845/emoticons/eek.gif.771b7a90cf45cabdc554ff1121c21c4a.gif
edit: Nickelback is lumberjack music just like Creed

lately ive been jammin on Buckethead