[kdh454]

Depending on your existing setup, adding tweeters to the A pillars may not produce a very desirable sound.

Ideally, you want your left and right speakers equidistant from the center of your head. Of course, that is not practical in a truck cab, so the best you can do is to get the distances as close as possible. Generally this means placing the speakers as far away as possible to minimize the difference. Moving the speakers higher in the cab, as with the A pillar pods, drastically shortens the distance to the driver side speaker and slightly decreases the distance to the passenger side speaker. The end result is hearing sound out of the speaker right in front of your face and not being able to hear the passenger side speaker. This effect is even greater with higher frequencies (tweeters).

If possible, I'd suggest temporarily affixing a set of tweeters in that location and see how it sounds. Tweeters are very sensitive to the direction they are pointed so make sure it is as close as possible to the location they would be mounted in the A pillar. If you like it, go for it. If not, look into another location to mount them.

If your at all handy with fiberglass, it would be pretty simple to make your own pod and affix it to your existing A pillars. Doing so would allow you to play with the position and determine what sounds best. Some people (and some manufacturers) angle the tweeter towards the windshield and bounce the sound off it to get the best sound. Do whatever works for you.