EDIT: I was writing this while Aaronz was writing his, may be some repetitive content.
1. Right, I confused myself with the attenuation and electronic vs. passive.
Most you can attenuate the tweeters 0dB and -3dB for example. You can buy separate electronic crossovers for car audio for serious tweaking, but the average listener doesn't need it.
2. Crossovers create a certain passband to send certain frequencies to the different types of drivers in your audio system. Passive crossovers are fixed, but with electronic crossovers you can modify the settings. I was talking about active crossovers here. You don't send a 20hz signal to a tweeter and you don't send a 5kHz signal to a subwoofer.
You do criss cross the frequencies between drivers to gently mix them together- but you generally don't want to send 500hz to a subwoofer, why would you do that when your mains speakers can handle 500hz just fine? It is well known that different sound sources producing the same frequencies can cause cancellations... quote from acoustic designer Bill Fitzmaurice:
Originally Posted by Bill Fitzmaurice
...you'll get major cancellation issues if you're running into the subwoofer range with either monitors or cans.
Of course a lot of other things can cause cancellations too, like reflections off walls and room modes and such, but this is more useful in a different setting, and car audio and home audio are vastly different so I should have mentioned that. The steep cabin gain of a car makes room modes moot. And I definitely encouraged playing with crossover settings?
Originally Posted by forester06x
It's fun to play with the crossover and see how your settings influence the sound. There are no specific rules that you MUST follow, just use what sounds best to you.
3. Right again, I confused myself with my 100hz lowpass on my subwoofer and 80hz localization frequency. I believe that "localization" is kind of user-defined. I mean, if you go to the middle of a field and put one subwoofer 50 feet from your left ear and play a 60hz tone through it, you should be able to tell that the sound is coming from the left, right? But is that true "localization"? Could you find a subwoofer producing a 60hz tone in a living room with your eyes closed? But generally, 80hz is considered to be the cutoff frequency for localization. Again I mentioned that this is more useful in home theatre.
I need to have my memory checked.