Looking at the Polk Monitor line (and most other floorstanding speakers), there are floorstanding with one, two, three, and even four 6.5'' midrange drivers, but all of them only has a single tweeter.
Can somebody explain to me why a floorstanding version of a speaker may have 2 or more identical midrange drivers, but only one tweeter, no matter how many midrange drivers a speaker has? Why aren't tweeters added?
Also, I know for every doubling of the number of drivers, there is a 6dB increase in sensitivity. Why can speakers achieve the 6dB increase in sensitivity with only doubling of midrange drivers?