Notice how the speaker grills wrap around to the back of the keyboard, apparently, with some sound coming out in that direction as well. That’s something I’ve been requesting of Yamaha on the PSR series, for those occasions where no external sound is needed, but just that little extra provided by the internal sound system-----so that some of the sound projects toward the audience and not all of it directly up toward the player.
It looks like just a bass port not a speaker in back...the truth will emerge when you see and hear demos of MZ X500 players in their house.....not a company promo edited one.