These are two different Rectify Series drop-in speaker systems for current-run Athearn Genesis and RTR locomotives that come with the "dual-cube" speaker or weight. The speakers use the factory mounting screws to mount to the plate or into the locomotive and no modifications are needed to replace the factory speaker or weight.
The UNI1 fits many of the new Genesis units, including the AC4400CW, Dash 9s, SD70ACu, SD80/90MAc, F59PHI and others. It will drop-on to the current RTR SD40-2s mounting plate, but I do make a specific speaker for these that replaces the stock plate and sounds a touch deeper: https://www.scalesoundsystems.com/product-page/athearn-rtr-universal-sd39-40-2-current-run
The UNI2 fit's the current-run SD60M, SD70ACe, SD70M-2, DDA40X, RTR SD40T-2 and will drop-in to the weight of the current Genesis GP38-50s. I do make a specific speaker for the GP38-50 that replaces the stock weight and sounds a touch deeper: https://www.scalesoundsystems.com/product-page/athearn-genesis-gp38-39-40-49-50
Simply measure the stock speaker or weight to determine which size of UNI you need.
The speakers come fully assembled and tested.
Dimensions are:
UNI1: 13mmH x 17mmW x 38mmL
UNI2: 13mmH x 13mmW x 34mmL
VIDEO: https://youtu.be/qSH9YU--1Dk