Does anyone know.....I already have plenty of bass in my truck but I dont want to replace the stock speakers. Can I just buy tweeters separately and get the same kinda loud music I want? Like just the voice, I have plenty of bass and dont need a midrange.
Of course you can add only tweeters (with the proper capacitor filter which is usually supplied) and keep your stock speakers.
The result you'll have depends on the specifications of tweeters you'll use (sensitivity, response, quality).
For example a sensitive tweeter (over 90dB) will have more efffect in your music than a less sensitive one. Another example is that a narrower range tweeter (i.e. 6KHz to 20KHz) will amplify only high frequencies leaving the rest as you hear them today, while a wider range tweeter (i.e. 2KHz to 20KHz) will also add a cleared result even to vocals.
In conclusion, it seems that you can do anything you like but you'll need some experimentation first.