When Carl-Mikael visited I got a home a package of a bunch of piezo disks. So we decided to try out an idea that Kristian Blåsol (link below) tried when he visited me. Lots of visiting. Putting 2 speakers up against the piano and connecting contact mics to the strings that thru a mixer goes to the speakers will create a wonderful feedback loop! YOOU SHOULD TRY IT!