These are Rectify Series drop-in speaker systems for Athearn RTR U50 (and very early Genesis U50) locomotives. The rear-mount speaker uses carpet-tape or a touch of adhesive to secure it to the frame. The front-mount speaker uses the factory mounting screws. No modifications are needed.
 
Depending on the stock electronics package, some PCBs may need to be moved (or maybe even removed). The RTR models I have seen have multiple PCBs and wires running everywhere - for no logical reason. A clean, simple decoder install sing a Decoder Buddy, Direct or PNP style decoder simplifies all of this and makes it much cleaner.
 
The speaker comes fully assembled and tested.
 
Dimensions are:
26mmH x 18mmW x 24mmL (rear)
10mmH x 18mmW x 29mmL (front)
 
VIDEO: https://youtu.be/f6jvmz6r66Y