You'll need flexible filament for this one! Here's a quick video of how effective this turned out to be:
Okay, so as should be apparent, the point of this is to reduce the sound level of a banjo, which is not a quiet instrument. It's a simple block that clamps over the bridge and strings to absorb vibrations, and it does the job reasonably effectively.
However, it certainly doesn't improve the quality of the sound! If you've ever used a metal banjo mute, you'll know it ends up kind of guitar-like, with softer, more sustained notes. This printed mute muffles things instead. That said, it does work, so hooray! This was really just an experiement to see if it was at all possible, so from that point of view it's not a bad outcome. I'm not likely to actually use it, though, unless I can't find my fancy commercial mute :)