Ok, I tested multiple sound units on two different fairings. The two fairings I used were a Windjammer III, and a Windjammer IV. The results between the two fairings were pretty much the same. I didn't notice any issues with the older smaller speaker units vs the newer larger speaker units. The larger speaker Cycle Sound and Vetter sound did seem to fit a little better, they were tucked back more and utilized the bracket to tie into the upper windshield bolts. Also, the older units just bolted the unit directly to the upper windshield bolt vs using a bracket. You will see in the images I tool below.
Windjammer III older smaller speaker Cycle Sound (I put the bracket on for reference) Notice the screwdriver in the windshield mount holes.
Windjammer III with larger speaker Cycle Sound
Vetter Sound with larger speaker (only way Vetter Sound units came) on a Windjammer III
Larger speaker Cycle Sound mounted on a Windjammer IV. Using the brackets
This is an early (can tell by the sticker and not and emblem) Cycle Sound, smaller speaker on a WJ3