Might muffel sound but I wonder if the metal infront of what would be the speaker opening should stay and some relatively sound transmitting fabric covers it?
Further research has learned me that is for either rear defrost air inlet or speaker- one or the other. My car was luxuriously optioned with neither. I may use that opening for a speaker with a 1965ish grille/cover but the project at hand is the rear seat and carpet trim with their the 47 thousand screw holes under new carpet.
