When testing the tweeter be sure to feed the speaker a signal that will truly test the tweeter. B&W sets there crossover for the tweeter rather high for the 800 series floorstanders. All vocals and 95 percent of the fundamental frequencies from classical music are actually handled by the midrange. B&W does a pretty good job of integrating the midrange with the tweeter but if you divert your ear from the midrange (i.e. hold a piece of foam or some other absorbing material at 90 degrees to the cabinet just below the tweeter and listen directly (close up) to the tweeter, you can find the source material that will be a good test disc. You may be surprised. Rock music with high end guitar riffs is the easiest source to test the tweeter,or a test disc with a range of tones. Of course once you find the proper source material then increase the volume and move back. If the tweeter is damaged and still 'works' you will hear it at high volumes -likely as a very noticible intermittent 'rasp' it will be obvious and will not require any guesswork. Just be sure to listen to your source material on a known good system beforehand. Much more common for the top mounted tweeter is damage that can be observed by careful visual inspection, tykes and inquisitive adults have a habit of 'pushing the button' - jamming their finger into the tweeter.