Thank you for undertaking this incredible work! I've contacted Thingiverse/makerbot about why our stethoscope isn't even showing up in the search results at this point. It's odd for sure. I have a few comments that I think will help contextualize some of the decisions our team made and hopefully improve your stethoscope as well! Please think of this as us with our academic thinking caps on, trying to make your project better.
This ties into why our design has hardly changed since we validated it - we found even small changes altered the acoustics in unexpected ways and occasionally brought us back to square one. I suspect that taking away plastic in the head would affect the acoustics significantly, but obviously I can't know without testing.
re: the spring: This is great and I'd love to copy back your design into OpenSCAD after trying it out. We've been noticing and are working on the same issue if you see our newest github branch that mixes this with a few other eartube modifications (straightened_eartubes)
Please change back the latex tubing to silicone. At this point, latex is not an acceptable material for medical devices unless completely unavoidable. This is due to allergies in between 2-17% of healthcare workers depending on reference, and anaphylactic (potentially fatal) reactions in a non-trivial number of people in the population. See: https://link.springer.com/article/10.2165/00139709-200423020-00005
Also, our goal here is to bring down the cost of high quality stethoscopes available to everybody. If a company goes and makes a huge run of your stethoscope design, the result of that is they will drop the cost of high quality stethoscopes available to doctors - our goal. If they make money doing it, that personally doesn't bother me, as it's their tooling, etc. I think most companies in the biomedical space would be sufficiently worried that they would probably try to license your design even if you don't require it. Adding the ShareAlike clause means that any modifications made would have to be shared back to you.
In short, to make your stethoscope design not a hobby project but something meaningful to doctors and patients everywhere, pick CC-By-SA.
All of this to say: It is beyond wonderful that you have done this, and I think your design is an important contribution!
tarek : )