mixing ohms in a crossover

the measure rating that they give you is the lowest it will ever go, but what you want is an impedance( resistance at work) meter (very expensive). while at school we used one to check the impedance on a 4 ohm rockford punch 12. between 20 hz and 120 hz we got readings as high as 92 ohms and as low as 5.3 ohms.  the rating they give is always the lowest that the speaker can go.so don't worry about trying to get lower on a tweeeter . or midrage. sure  if you lower the resistance than you'l get more power to them , but you;ll lose sound quality too. keep them in as they are. the crossover will be okay. and sound ok. . good luck