This stethoscope head has a 0.2mm membrane that is enabled by modern 3D printers' excellent first layer continuity. Good printer cooling enables printing without internal supports despite steep overhang geometry.

Be sure to plug the top-hole with your finger if using the membrane side directly. The sound quality is not perfect, but I can at least get a sonogram of my heartbeat when I connect to a microphone. Since amplification is low, the room must be quiet to hear a heartbeat properly.

The 7.5mm outer diameter, 4mm inner diameter tube adapter will fit inside a silicone tube with 1/4" internal diameter with some stretch. The earpiece to ear gaskets can be made of the same tube. I used this tube size because I had some on hand.

A smaller tube may enable better sound amplification, but I've not tried this. Let me know in comments if you want parts made for other diameter tubes.