Put your hand on the screen (with a glove, if you have grubby fingers) and you'll feel it vibrate in the way of a speaker cone. Don't worry about blurry images: you don't see the vibrations, because it operates at such a high frequency. Low-frequency notes, which would be visible, are handled by the separate subwoofer.
How does it sound? To my surprise, rather good. Admittedly, I've never heard this technology before, so I have no frame of reference, but I'd say it sounds better than plenty of regular TV speakers that sit at the side/bottom/rear. It's a clear, detailed sound that never hardens, even when it gets loud (and it gets loud), and there's a good amount of weight to it, too.
What's really surprising is the way the sound follows the action on-screen and off. You can track voices to people's mouths and explosions go where they should. The stereo image is good enough that the sound does a great job off-screen, both vertically and horizontally. Such precision in effects placement is something I'd only associate with surround sound systems, or Dolby Atmos, or really clever Yamaha soundbars but not a TV.
Granted, it isn't the cinematic sound you'd get from a pair of proper speakers the A1 doesn't have the dynamism or room-filling power but it does a great job on its own. I'd love for this to become a standard feature on OLED TVs.