I'll try seeing if changing it around 50 does anything, I remember trying 51, 52, and 53 but it didn't really do anything. I'll try Dan's suggestion, it sounds more like my problem because I think the sound is being distorted from mine.
Like I said, try to keep it around 50 (that's what it says in the documentation, anyhow). Did you try it at 51/52/53? Or 49/48/47? I'm not quite sure what it does, to be honest. You might ask Lucas Garron, I know he currently maintains the project. You might also ask Walter Sousa (might have spelled his name wrong, owner of Prisma Puzzle Timer), as he has included stackmat compatibility in his project.