My active xover doesn't include a notch filter in the tweeters leg so something had to be done to tame the effect of the waveguide. The filter shown is quite simple and provides a very useful response that can be shaped into anything really, when using only a bunch of high pass filters.

No doubt I could have changed the filter values to make the impedance a tad easier on an amplifier, but I had to work with the components I had on hand.