These are Rectify Series drop-in speakers for Intermountain F-Unit locomotives. Two A-Unit versions are available; early-run non-sound and current-run sound-ready.
 
Two B-Unit versions are available, fitting the space where the cab would be; early-run non-sound and current-run sound-ready. You can use these speakers singly or combined with one of the rear-mount speakers for maximum impact.
 
More than just a box, the enclosures feature 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 speakers use carpet-tape or a touch of adhesive to mount and no modifications are needed to replace the factory speaker.
 
The speakers comes fully assembled and tested.
 
Dimensions are:
Early A-Unit F700: 12mmH x 26mmW x 32mmL
Early B-Unit B700: 12mmH x 26mmW x 30mmL
Current A-Unit F701: 13mmH x 28mmW x 40mmL
Current B-Unit BOMB: 16mmH x 30mmW x 41mmL