I had run across this a little while back, quick search and found it again, DIY clip on mic for harmonica in a rack
image.jpegHey ,I've been.making hands free harp holders so I can play harp one handed since I lost my left hand years ago . I have one you mite find useful. I make them from aluminum stock and they screw onto a Shure 58. The slot has wiper blade that hold the harp and act as a seal.Here are some photos .image.jpeg
Just sent a post with some photos ,but the ones displayed aren't the ones I sent ? How to fix ? Ron
I'd do it the same way musician's have done it for decades. Small lightweight bracket around your neck that holds harmonica and has a clip on mic. A mic like that will work so much better than a piezo. You could use the C.B.Gitty Tin Can Mic if you want that old time echo effect.
Clip on mic a few inches from the front. If too close, it will pick up the nearest holes more than others. Neil Young on 'Rust Never Sleeps' seems to have 2 mics mounted on his rack. Some sort of Piezo might work but again it might pick up some notes more than others.
or what this guy did <iframe width="475" height="267" src="https://www.youtube.com/embed/66cBRiZQOTU" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>
In the photo you see a harp with a contact Mic/transducer attached, I just tried it and it picks up the nearest reads ,as mentioned by Fergus, but also all the touching and extra noises.
Then I thought that this might work. Also in the photo is my Green Bullet Shure harp mic, it is normally mounted on a mic stand [you can see the modified fitting]. It is the same stand that I use for vocals, but has two booms side buy side, one for vocal mic and the other for the harp. I just swap between them as needed, but I play using my hands. If I wanted hands free I would mount my neck harp holder to the boom and then have the harp set up for best sound in front of the mic. I am constantly swapping keys so having the mic not attached to the harp is good. Food for thought.