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802 "D" Stands for the the fact the tweeter domes are made of pure diamond.
The "S" Suffixed models a less costly aluminum dome used in the Nautili.
The manufacturing process involves chemical vapour deposition at 1,000 degree Celcius and then laser trimming. The reason B&W chose diamond is because it is the stiffest material on earth so in theory it should produce the stiffest dome which in turn ensures its first break-up resonance is at a signifigantly higher frequency than an aluminium alloy dome. Disadvatnage might be they are heavier than beryllium, titanium, aluminium but they claim the advantages out way this problem. Where the resonace peak of the S line is around 32kHz the diamomnd is around 74kHz some two octave above the human hearing.
Other new features like new surround material also have lowered the fundemental resonance and thus allowed a gentler-slope, single-component, first-order crossover feed. Also a new capacitor from German company Mundorf was also specialy developed for the 800's speaker range.
All new 800 series use B&W surroundless FST midrange driver (minus the 805). The idea being the midrange driver does not need to make the substantial excursions required for bass/mid drivers and therefore can make use of special material to absorb the vibrations of the woven kevlar driver. The use of Klippel's computer modelling techniques helped refine the FST driver over the previous generations and why they use of a plastic "bullet" polepiece extensiosn, as metal is better avoided here.
Also new bass units in a sandwich diaphram made from 8mm thick Rohacell structural froam, laminated between woven carbon fibre, providing high structural stiffness and minimising the transmision of sound from inside the enclosure.
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