Hanging a carbon filter?

Lets say I just hang the carbon filter in my grow cab....will this do or must it be placed before an exhuast outlet?

The nose knows. Dont ask us, ask your nose! I can't smell it can you?

Are you talking about just hanging it from the ceiling with no vent attached? If so, that wont do anything.. You need to push or pull the air through the carbon scrubber to filter out the smell..