This is a Rectify Series drop-in speaker system for Athearn Genesis ES44AC/DC locomotives. More than just a box, the enclosure features Diapasonic Tuning™, which allows the lower frequencies to accurately develop and resonate, clears the midrange of excess resonance and tunes the upper-mid/high response. The speaker has two pins that locate the system in the frame, just like the stock speaker. A single screw-removal is all that is needed to remove the stock speaker/frame. This system then simply drops-in and I use a bit of carpet-tape to keep it in place.
 
The speaker comes fully assembled and tested.
 
Overall dimensions are 31mmH x 18mmW x 28mmL