I kinda figured with your handle, you could just hook up a sub-woofer and get a far superior effect to that of a french horn. I remember one festival where we made the "sitting box" basically just a box with two sub-woofers in it pushing enough peak electricity to power my grow. We painted it and put LEDs in it to make it look a little less like a multi-person rectangular sybian, but that's what it was.
I played my electric cello at that event through the ograsma-box, I collected a nice set of groupies shortly after laying into my low C string while playing my Drum-n-Bach set.