But Dr. Toole the only thing memorable about the NS1000 was its Beryllium drivers. Why?
Not just because they were exotic stuff! As I've said, beryllium made possible to manufacture a midrange dome of 3.5in capable of operate from just below 500Hz to above 6kHz.
As you say, directivity is determined by dimensions and I'll also add shape. A dome is omnidirectional provided it doesn't start to exhibit breakup modes! That's what characterizes dome tweeters. Now try to produce a dome that is able to operate in such wide frequency range at 90dB (1m, 1 watt) with materials other than beryllium. ATC being able to produce a proper 75mm (3in.) soft dome mid-range driver is some sort of engineering miracle (but it doesn't go as high in the frequency range nor it has the same efficiency)! Midrange transperancy is greatly enhanced with such dome drivers and I bet beryllium has the edge (pun intended) over textile domes. Isn't that why Revel uses metal drivers after all?!
Two-way loudspeakers, by definition, don't benefit of such midrange dome, so for every two-way design there will always be that inherent limitation, which will always be their biggest enginneering challenge if one wants decent bass output.
I guess that paper simply wasn't good enough of a material for such big cone and made it even worse in the NS10M! Monitor Audio latest Silver 100s are a two-way design with a 8" woofer and an even higher crossover point (2.8kHz against 2.0kHz of the NS10M) and don't sound remotely as bad.
But I'm sure that a beryllium tweeter would have allowed to lower the crossover frequency in the NS10M (as it happens w/ Revel Performa Be models range) and therefore would have helped to mitigate the phenomenon.
Oddly enough, when using the NS10M "recording engineers sought to dull its treble response by hanging tissue paper in front of it, resulting in what became known as the "tissue paper effect".
As for the driver motors, stiffer, lighter driver materials allow the usage of bigger, more powerful motors for the the same (or less) driver net weight, which helps heat dissipation, meaning they run cooler and hence with less heat compression at high SPLs, while keeping efficiency by virtue of the reduced weight.
On the other hand, one can see in the NS1000M owner's manual
how the elevated axial frequency response can be tamed with the level control set to -3dB.
Finally, the same way smartphones, laptops and the likes have paved the way for electric cars with the battery tecnhology becoming increasingly better and cheaper, I also believe that automotive industry will help carbon fiber to be readily available for many other applications at a competitive cost, such as loudspeakers drivers!
Revel Salon3 CF... sounds goooood!!!