How big are your LMB? An 8-9"+ LMB should prey on 3-4" Crappie. If the crappie survive and grow, though, they compete directly with your LMB for food and could have a negative effect. Your pond is 4 acres, right? In water bodies that size and smaller, crappie and LMB don't play well together.

"Only after sorrow's hand has bowed your head will life become truly real to you; then you will acquire the noble spirituality which intensifies the reality of life. I go to an all-powerful God. Beyond that I have no knowledge--no fear--only faith."