Where to mount them then? Kick panels, sails or elsewhere?
We often see tweeters mounted up high on the sail area on the door or down in the kick panels. Both these work well but can suffer from similar issues. The problem with the sail mounts is this; think about the position of your ears in relation to the tweeters. One speaker is belting the high pitch tunes out about one foot from your ear where as the other tweeter is triple, quadruple or quintuple that distance away. The image has no choice but to be right out the side window. Sheer laws of physics govern this fact. If you place the tweeters down in the kick panels then the right speaker distance is about three feet and the left speaker is about four feet away. The problem is not utterly eradicated but it becomes a lot less noticeable as the distance separation is reduced (by up to half sometimes). However using the kick panel method the stage can be a tad low (the kicks are often used on cars with no factory tweeter location to avoid the cost of custom A-pillars or sails too).