I'm thinking of installing an 8"or 10" subwoofer in my RX-8. Should I get 6 1/2" door speakers or would smaller 5" or 4" speakers be better and lighter? Does the bass in the 6 1/2" duplicate much of the subwoofers frequencies, so that a smaller speaker would be adequate?

 

The speakers do need to overlap so that they blend well. Depending on the components and the subs, a 6 1/2" set might blend in better, especially if the subs are in a ported or bandpass enclosure. With proper crossover settings, nothing will be "duplicated".

---jps