Ripped apart my dash today to see if I could squeeze a center channel speaker in the vent.
It's great the vent runs like a tunnel. Starting on the wide (left) side it is 7" wide and 1.5" on the Small (right side inside. The a/c duct also is pretty deep then reduces down in size. Also the vent in the dash has two parts! The outside part that everyone uses to adjust air alow and a inside grill part which can be removed for more clearance. Just have to figure what will sound best having a 4 mid laying down pointing up or angled almost vertical. Plenty of room for my 2 tweets also. Hello bostons here I come.