I forgot about the lower volumes
Heres a suggestion that might help the meadowlarks .
You,ve already said you,ve got them on slabs , so its not much of a chore .
go get a couple of bike inner tubes .
stick one under each slab .
you,ll have to slide the speakers around a bit till you get them balancing properly . Mark the positions on the slabs . Take the speakers of the slabs and put a few blobs of blue tak down (i,m wondering that if the speakers are sitting straight on the slabs that your introducing some very small rocking )sit the speakers on the blu tak somewhere near your marks .
It is a temp solution , but I think you,ll get some mileage from this .
speakers sat on air plats don,t move when the music is playing , only when you give them a push .
trust me ....... i,m an idiot