The speakers are rated at 140 watts. They sound great without an amp, but if you add an amp, you can run a good amp like the Biketronics Titan BT480 or Hawg Wired equivalent. They are designed to run with the stock Harman/Kardon headunit, but J&M does state that you can run them with an external amp with no problem. I just installed them in my 09 Street Glide today and I can tell you that you really don't need an amp.
Shawn