Bowers & Wilkins Zeppelin Owner's Manual page 41

Midrange The twin midrange drive units that
supply the bulk of Zeppelin's amazing sound
rely on glass fibre cones, optimised using laser
interferometry. Strategically placed resin-filled
slots in the cones dramatically reduce the
unwanted effects of standing waves, leaving
music sounding cleaner, clearer and true to life.
Ultra-wide sound The less physical material
there is around tweeters and midranges, the
better they sound. Zeppelin's rounded, tapering
ends aren't there just for show. By minimising
the baffle area around the drive units, the
cabinet reduces diffraction effects, making
for ultra-wide sound dispersion and a much
smoother response. In other words, it sounds
as good as it looks.