These are drop-in speakers for the Bachmann sound-equipped FA and FB locomotives. 
 
The FA locomotive uses the RAPO-E8XR in the rear position and the LLPR-PAXF for the front position. Double-sided mounting-tape and/or a strap of Kapton tape is used to secure the speakers.
 
The FB locomotive uses one or two of the RAPO-E8XR in either position. Double-sided mounting-tape and/or a strap of Kapton tape is used to secure the speakers.
 
No modifications are required to replace the stock speakers. The speaker(s) come assembled and tested.