No barriers on air for smart alecs (4-4)
I believe the answer is:
know-alls
'smart alecs' is the definition.
(I've seen this before)
'no barriers on air' is the wordplay.
'barriers' becomes 'walls'.
'on' says to put letters next to each other.
'air' becomes 'k' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'no'+'walls'='nowalls'
'nowalls' put after 'k' is 'KNOW-ALLS'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for know-alls that I've seen before include "Smart alecs" , "People who think they have encyclopedic brains" , "People who behave as if they are conversant with everything" .)