For the BLI SD40-2s, the ALMA-QSI1 speaker replaces the stock speaker.
 
The ALMA-QSI1-RC1 is a half-round shaped system that fits within the a-frame speaker mount and fires down over the drive-shaft. No modifications are needed to install the speaker. Simply remove the stock speaker and use strips of double-sided mounting tape to secure the Scale Sound Systems speaker within the frame. See the second photo showing the steps to do this.
 
Note that you need to set the master volume to around 60 on the Paragon 4 decoder. Doing this even with the stock speaker will reduce the crackling and rattle that occurs out of the box. This volume setting still produces plenty of volume and the broader frequency-range of the SSS speaker will greatly enhance the overall sound.
 
The speaker comes fully assembled and tested.
 
Dimensions: 16mmH x 18mmW x 27mm Dia.
 
VIDEO: https://youtu.be/DyBwqmKRy2I