With CVD diamond and alpha corundum ceramics we have already two of the very best membrane materials on earth, so why search for a new one?
Let's summarize it: CVD diamond is definitely the best material available. It's stiffness to weight ratio is unsurpassed, the internal sound velocity unrivaled. However, until today, we can only make tweeter and small midrange units, cost and serious technical problems prevent the manufacturing of larger cones. It is quite similar with ceramic domes, these are second to and almost as good as diamond (still better than anything else exept diamond) but also restricted in size. The largest dome we can feasibly produce is a 160mm dome for the C220 series.
Doing research for larger bass cones we found some interesting results. Laser scans of moving membranes taught us that the voice coil area is the most critical and deformation is strongest here while the outer area is fairly stable (this is however only valid for concave domes like we build, not for different membrane shapes).
So we took a special, exclusively made for us, white honeycomb membrane and doubled it up with a fitting, asymmetrically shaped ceramic dome (to put one and a half year of tedious research into one sentence). Let's look at the benefits:
* Large cones (up to 15 inch basses) are economically producible
* Stiffness in the VC area is even better as with a pure ceramic cone
* Outer area has very high damping factor, the unit is easily usable with a first order passive filter
* The ceramic part of the dome (S280 and S220 models) has an asymmetrical (Wankel) shape, killing resonances
* The aluminum honeycomb sandwich of the AS models (AS 250, AS 190, AS 168) has extremely good stiffness to weight ratio and an acoustic center in front of the speaker baffle
* The cone is almost indestructible, even at severe overload (remember, you can still burn the voice coil!)
Bandwith and resolution is almost, but however not as good as with a ceramic cone but this, after all, is not so important for a pure bass unit.