cubic target selection functions improperly

i have a repeating command block pointing at a chain command block.

in the repeating command block set to unconditional and always active i use this command:
testfor @a[x=-617,y=57,z=-734,dx=-567,dy=57,dz=-694]

and in the chain block set to conditional and always active i use this command:
say IT WORKS

What i expect to happen, is when i step into the area within those coords, i want the chain block to say "IT WORKS!" repeatedly, but to stop saying it when im ouitside the area.

However, it seems to say "IT WORKS" whenever i am at y=57 and above, and seems to say it when im in an incredibly large area outside of the x and z coords i typed in.