I designed and built my own planar ribbon drivers and made them into an iem! The whole thing took over two years and countless driver prototypes. Final product is a 2x 9.2mm dyanamic driver (in push-push configuration) for bass, and a dual planar ribbon driver for mids + highs. Sound is extremely clear and detailed, and bass extension is wow. The bass really feels like someone is punching your head.
I actually made two single driver full range prototypes before this, but the driver sensitivity isn't great, so the bass was very flat. I had to add dynamic drivers to get a bass shelf without killing the sensitivity.
Driver was very difficult to build, and I can't count how many different designs I've tested before ending up with this one. Ran into many obstacles, from what type of glue to use in certain places, the design of the traces, finding a factory capable of printint the diaphragm, and how to attach the lead wires on to the solder pads and diaphragm. I've mostly resorted to using silicon glue as it is more heat resistant and super glue will actually break the diaphragm. The driver can take a LOT of power, I can drive it on max volume on my AT-HA5000 for a long time without damaging it.
Why a planar ribbon? It was simply because I thought it'd be fun to build one since I haven't seen it done in an DIY IEM before.
Can the driver be mass produced? Probably not - it was very costly to make a single driver, and the successful rate of matching two drivers are pretty abysmal. The success rate of assembling the driver is actually VERY low considering that the diaphragm is printed and cut from a factory and pretty much all the parts are CNC'd for accuracy. Also, the treble is impossible to match, and many variables can change its response, including temperature, how much resin is used, or even if you looked at it the wrong way lol
Was it fun though? Yes! I'll keep working on the design improvements when I get the time (and money). I'd love to answer any questions if you guys have any :P
