The most fragile speaker that i met for B&W 800D2 tweeter

Hi , i got a B&W 800D2 serial No. 0001373 & using mcintosh MA6700 to test the sound n when i push up to volume 40 the twitter surface start crack line. but my twitter still perform very well the sound.
could any body advice when causing this n how to repair?


Richard Ling