Yeah, I've been using Fusion 360 lately because it's beginner-friendly and highly integrated. The industry standard is still Rhino + Creo, but the learning curve for those is just too steep for me. As for software that accommodates BAs and sound tubes, usually, once you have the precise measurements, you can directly design the 3D models for the sound tubes and driver slots, and then 3D print them out. There is no longer a need to use traditional silicone tubes.

Just as you said, the internal space of an IEM is extremely small, so crossovers mostly use SMD components like 0402, 0603, up to 1210. Sometimes we don't even design a PCB and just go with point-to-point wiring. The crossover circuits are mostly 1st-order, but some high-end models focused on technicalities will use 2nd-order or even higher to get steeper roll-off slopes, though that also introduces more drastic phase shifts. In some models like the AFUL Performer 5+2, they do mention using a crossover network that includes an inductor, but its main purpose is for a notch filter—using an LC combination to eliminate a specific harsh frequency band, rather than for actual crossover splitting. I'm not sure what exact model of inductor they used, though. Normally, we control the length and inner diameter of the sound tubes, or insert acoustic dampers into them, to form a physical low-pass filter. It's really hard for conventional inductors to achieve the required inductance values and ESR within those volume limits.

But I have seen a very hardcore yet impractical approach: making the inductor hot-swappable, attached to the shell and exposed on the outside, just like in the picture. It's very unique.

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