This is a Rectify Series drop-in speaker system for Athearn RTR RS-3 locomotives. The speaker replaces the plastic tray in the long hood and no modifications are needed to replace the factory speaker.
 
Shown is a mock-up of the speaker installed with a Tsunami2 PNP board placed over the motor. The top PCB mounts may need to be slightly filed down for a board like this to fit correctly. A small hardwired decoder should pose no fit problems.
 
The speaker comes fully assembled and tested.
 
Dimensions are: 9.5mmH x 18mmW x 40mmL