Also:
2 tweeters that roll off at the example freq or 22khz and 33khz will also have a phase shift difference even well below their roll off freq, in the audioable range. Much of music is composed of impluses which are composed of the fundamental freq and some harmonics of that freq. If the phase relation of these harmonics are affected by the tweeter roll of freq, then you change its sound.
2 tweeters that roll off at the example freq or 22khz and 33khz will also have a phase shift difference even well below their roll off freq, in the audioable range. Much of music is composed of impluses which are composed of the fundamental freq and some harmonics of that freq. If the phase relation of these harmonics are affected by the tweeter roll of freq, then you change its sound.