also the power to make the higher frequency levels is much lower than it is when you start to get into the lower frequency levels. also the small size is relevant to what the speaker reproduces. since the wavelength on higher frequencies is shorter, you need a speaker that can react extremely quick to reproduce that frequency. as for lower frequencies, thats why speakers start to get larger in size. this is because the wavelength starts to stretch out and the speaker would move drastically slower than the cone of the tweeter. hence why cetain speakers only do certain things. if you get the chance find someone with a good setup in their car and watch, at a safe volume, the subwoofer or other large speaker during a sine wave track or a "sine bomb" some refer it to, and you can see how the speaker reacts at the different frequency levels.