Do Undercover Car Speakers Sound Good?

I have a 1962 ford falcon. The sound system is horrible as expected. I don't want to extremely modify my car, so what i'm looking into is purchasing "undercover" car speakers, which are powerful speakers that fit conveniently under my bench seat. My question is will they sound muffled being under there or will it be a clean, crisp sound. Also I will be putting a new radio in the glove box so i don't disturb the original one, will it be a hard hookup to get this set up properly? Thanks, Robby