I've got a solution. This device is easy to make yourself. You just need a few basic supplies:
  • a thin piece of plywood to serve as the backing material
  • a copper sheet
  • four screws
  • glue
  • lamp cord
Here's the assembly procedure:
  1. Cut the plywood into a square about the same size as the top of your speaker.
  2. Cut four squares of copper small enough to cover most of the plywood but to leave some room in between each piece.
  3. Glue the copper to the plywood.
  4. Take the lamp cord and separate both the negative and the positive side into two separate strands, for a total of four strands of wire.
  5. Screw the negative ends of wire into plates diagonal from each other. Screw the positive ends to the remaining diagonal plates.
  6. Place your new Cat-Zapper on top of your speaker and then plug it in.

Really, you can use this to protect any horizontal surface from naughty felines.