It's a deep notch, maybe 20dB. I think it's the driver since 2 other drivers on the same horn don't have the notch, or not as bad. Both 288s do. I have someone helping me make it go away. Will try a different horn if I can.
The notch is narrow, about 1/7th octave, but I don't like it. I've tried to blend the tweeters over it, but no real luck. Too bad because with the proper HP shelf on the 288 + 1005 it can be flat to 15KHz. No need for a tweeter.