Yes, to stiffen but more importantly, the tubes are arranged standing up next to each other. This has a special effect on how the audio is presented but you need a scientist not an audio engineer
I seem to remember reading about proposed membrane speakers using CNT's, where the membrane isn't actually stiff, and the sound is produced by direct application of an electrical current, which causes the membrane itself to produce sound, as opposed to simply exploiting the stiffness of CNT's to manufacture a conventional stiff driver dome which is driven in the typical way by being suspended in a flexible surround and moving air by being pushed to and fore by a normal voice-coil like a piston.
I guess that current iem CNT drivers are still using the latter? (could be wrong here, I hope I am!)
If membrane CNT drivers are eventually used for sound reproduction then things could get interesting, as it might allow for the production of sound from a thin, flexible film, like planar tech' such as Electrostatic, magnetostatic and magneplanar, but without the interference of bulky magnet arrays or stators between the drive surface and the listener/ear. It would probably be more like NXT distributed mode tech' than current planar drivers, with nothing to block sound distribution.
I imagine that'll likely be exploited to produce high freq' sounds before bass, as bass requires more displacement, but perhaps the 'tubes stacked together like straws' arrangement can be coaxed into making bass too somehow, dunno.
I'm curious what an iem with just bone conduction drivers sounds like?
I know there are plenty of examples of 'skull-phones' like the Aftershokz, which I've heard, and was surprised by, but in-ear might be substantially different. I wonder what freq's Bob's bone drivers cover?
I certainly wouldnt choose the Aftershokz for critical listening, nowhere NEAR enough bass, quite apart from fidelity! But they did surprise me by not being totally unlistenable.
Exciting times for iem driver tech'.