no difference for me, although mfr says they are designed to play with them on. at best, I think with grills on, you keep dust and other particulates from settling on the components and damaging sunlight out too. (I am a little ocd about keeping things nice and clean.)
my Samoyed loves to sleep smack in front of the speakers with my music playing
my Samoyed loves to sleep smack in front of the speakers with my music playing