I've just saw this excellent sound library by echo collective where they used a stethoscope mic to record it http://ecbiz115.inmo...rgotten-zither. I didn't know such thing even existed. Is this actually manufactured by some company or it must be hand-built (in the last case, the question is how would someone do it?)
I did that recording.
(your link is broken btw. Here's the link.)
the mic is a Rode NT5 plugged into a stethoscope that I modified using a rubber end to a chair cap. Stethoscopes are really just the main chest pieces connected to some rubber tubing. Here are a couple of pics:
I got the idea from some diego stocco vids.
The key is to form an airtight seal around mic leading in from the tube. This setup has some pretty massive low end, but it does roll off the high end quite a bit. The recordings combine the stethoscope mic with the overhead CM3s.