Like the title says. When would you use one frequency over the other?
Depends on whether you want to talk to aliens near, or far... adjust your tin foil hat to suit.
As my deaf friend would have said; "What that mean?" Willie
well 50khz is good for deep water but 200khz is better for finding fish!
This may shed some light on the question: http://www.pavementinteractive.org/article/compaction-equipment/
For example of using both - The rock we work here, to get it to compact to good levels, For a single drum 12 Tonne Dynapack roller, we do 4 Passes on high vibes, and a minimum of 8 on low. That varies obviously but that gets our rock down and down well.