That pdf had a bit of BS, but I'm interested in hearing this stuff.  Should be an exciting year.

First post here in a long while, hopefully not too controversial! The white paper is indeed dodgy in some of the things beeing said. Coming to mind (I gave up half way thru):

1. Porous layers are non linear in their acoustic characteristics. Well, that's news to me (and shocking after all the time I've spent modeling / measuring fibrous materials and never ever seeing this supposed non-linearity).

2. Headphones all have free resonance characteristic of tweeters, e.g. Somewhere in the kHz range. Well, I am sorry to say, this is incorrect for the most part. I think the author is confusing the poor radiation efficiency of small suze diaphragms and high frequency of resonance. We all know for example that planars and other stats have a free air resonance in the 100hz range or lower.

3. Equating the efficient acoustic coupling of sealed earpad cavities with speakers loading a vehicle cabin. Well, actually the analogy is right in the sense of the acoustic impedance felt by the driver and resulting coupling. But the faults with a car woofer typically come from the first cabin modes (which you'll never get in a phone below 2kHz or so), not due to the loading mecanism.

Now, it's always exciting to hear about some innovative transducers so I definitely curious about this. My understanding of piezzo transducers is their very very limited displacement range (thus making them practical only as tweeters, I used to work with the famous Audax HD3P, quite something). So, I have my reservation about how you can get around this but I am very curious!

Cheers,
Arnaud