Why IDEEL?
Simply put: other options were found to be lacking. In our opinion, any audio connector for cables should be designed to support rotation of the cable, thousands of engagements, and guarantee polarity without user thought. Any connector that does not support these three features at a minimum are not suitable for heavy IEM use.
What about MMCX, you ask? MMCX was designed for RF applications where cables may be attached a few dozen times at most (500 is the design target, but we would rather not push that design target), and the cables are glued-in-place as rotations/movements of the cable will affect RF transmission efficiencies. This also results in the “four finger” connector which is not suitable for multiple rotations. So MMCX is out because it’s really not designed for a few hundred (or thousand) engagements, or for near-continual rotations if needed.
There are the two pin solutions from a wide variety of vendors. However, all of them require a specific alignment for proper polarity. This leads to consumer frustration (witness the Type C/Lightning connectors versus the older micro B style), and can be forced to engage even if not properly aligned. And an out-of-phase channel leads to a terrible audio experience. Add in plastic as the main mechanical engagement method, and there will be wear over time.
Thus, we decided upon IDEEL. Take a standard 3.5mm TRS. It’s designed for literally tens of thousands of insertions. It naturally supports a near-infinite number of rotations, thanks to the large engagement surfaces and the single-point connections of those surfaces. And it’s completely polarity free, thanks to the coaxial nature of the connections. So the decision was to make IDEEL a half-diameter, 1/3rd length TRS connector, thereby granting all the benefits of its larger cousins in a form factor that would fit in any IEM. Lay out the connectors along the length of the plug and the metal plug is supported only by the metal connectors in the jack, for incredibly long life.
Why Three Conductors?
Headphones are getting much more complex. Many are no longer just a speaker on the end of a wire. Microphones, sensors, indicators, controls - all exist in our ears today. A speaker (or group, fed through a crossover) needs at least two conductors. A 3rd conductor opens up a world of other possibilities. A microphone could be fed (along with the ground of the speaker, much like as in headphones with in-line mics) on the 3rd leg. Using a 1 wire serial bus (like that from Dallas Semiconductor) allows for multiplexing a variety of digital data AND power on the single conductor. You could even provide a bias voltage for an electrostatic solution, if so needed.
Bottom line - no one ever complained of having an extra conductor around in a cable harness. So we did it. Supply the two you need for the speaker, and leave a spare for custom applications.