I've heard you don't really need a crossover when yout do a midrange in the door and tweeter elsewhere type system. The fact that the tweeter doesn't work below (example) 3 kHz automatically makes its lower crossover 3 kHz. I know that crossovers make it cleaner and also give you the control about where its crossed over but even with that control can I honestly say where the best crossover point would be?? So if I didn't use a crossover with a co-axial and a tweeter; I would still get highs in the lower door's co-axial as well as get ambience highs in the tweeters that were mounted higher. Does this make sense??

 

Who told you that sending a full range signal to a speaker will just automagicly make this happen?

 

An ideal speaker could play all frequency ranges accurately. However, because no traditional speaker can do this an "ideal speaker" is created by combining two (or more) speakers. The purpose of the crossover in component speakers is to blend the two speakers together such that they sound as one and let each speaker perform in the range it does best (lowpass for the midrange and high pass for the tweeter).

To say that a tweeter automatically doesn't work below (example) 3kHz is simply not true. While it is true that tweeters do not perform well at low freqs, they do not "automatically" turn off. The added purpose of a high pass crossover for a tweeter is protection for the tweeter from these low freq. signals. This is the reason that all two way speakers contain a high pass filter for the tweeter (be it a fancy external 3rd or 4th order crossover in the case of most component speakers or a simple inline capacitor in the case of most coaxle speakers).

Not using a crossover (esp. for your tweeters) just does not make since either sonically or for the protection of your speakers.

Brett