Hardness (harder is better)
Flexibility (more is better)
Weight (light is better)
And TI figure out which is which.
Regardless... a car may have a V12 engine, but the outcome, how fast the car does a quarter mile or 0-60 is what matters.
Actually, I have a book ( "High Performance Loudspeakers" by Martin Colloms) which goes into this. It actually has a table that lists the material properties of a whole number of materials suitable for driver diaphragms, including Bextrane, Beryllium, Boron, Carbon fibre composite, Copper, Diamond, Magnesium, Wood, etc.
The science of it all is way over my head, but it specifically notes that:
I wish I could scan this stuff in but sadly can't get my scanner working atm, may try again later. But it lists the relevant figures as: Density (p), Young modolus (E), Specific modulus (E/p), Sonic Velocity ( Square root. (E/P), and the all important Q).
So essentially what it seems to suggest is that its a huge variety of factors and science that is far beyond what is actually provided in marketing materials. It repeatedly cites different manufacturers, particularly KEF's research in these fields. And this is just in regards to the material of the diaphragm - not the cone shape, voice coil, suspension, magnet, enclosure material, standing waves, diffraction due to enclosure shape, psychoacoustics, etc!
I don't know how this scales down to headphones but I'd imagine much the same, though probably they can experiment with more exotic materials / have greater challenges of miniaturisation.
If anyone is interested they perhaps might like to get a copy of the book :)
The FX40 and FXT90 both have carbon nanotube drivers. They've been shown to have excellent detail reproduction.
I'm intrigued by the fact it appears to be a(n arguably) more balanced, refined take on the FXT90.. which was definitely one of my favorite IEMs in recent memory. Tame the FXT's (mid)bass down a touch, add some clarity to the mids and coax some sparkle from the treble.. and hopefully widen the soundstage.. then JVC has a winner on their hands (and worthy successor to the FXT90), IMO.
That's what I'm banking on & my appreciation for the FXT90 was enough to warrant an FXD80 pre-order. Plus, they look badass. I've never been a huge fan of micro drivers but it looks like JVC is doing some pretty cutting edge stuff here.. my wallet must oblige.
Micro-drivers are awesome because you insert them deep in your ear canal which results in the transducer being closer to your eardrum which results in a different presentation of sound which is quite intimate, good with electronic music etc.
Apart from all the science a_recording (thanks!) posted the driver position (angle), distance, and size are all important factors to take into account, perhaps curvature too.
Why am I not aware of this thread earlier? My poor wallet... I'm in! In love with my FXT90, except for it's tendency to highlighting sibilance when a song has it, and the a bit too punchy bass.
The FXD80 looks really nice, I like the styling of them a lot. They use the same drivers like whats in the FXT90 but I hope they sound different because I'm not big on the sound signature of the FXT90. JVC has stepped they're game up the past year or so and have some nice IEM's now and even though the FXT90 isn't for me I still respect its technical capability.