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I have a Sony TV A9S with those actuators and, well, while it's far from bad, the cheapest Sonos Ray soundbar was a night-and-day improvement over the TV's "not-technically-speaker". Maybe it's good enough on the iPad though.
 
Touch can dampen sound by absorbing vibration. Apple could likely mitigate this with sensors that determine how the iPad is held, adjusting the vibration pattern accordingly.

"You're holding it wrong!"
 
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