If you turn the mono-tone, vibrators to their lowest setting, they don't sound too bad. Not anywhere near their price tag, but one could do a lot worse.
At first I thought "these would be kinda fun for teenagers" the whole concept of 'car-rattling-sub-woofer' style sound. But it's implemented so badly. The Vibrators only activate at a limited range and cuts off around 30-40hz.... so if a song has some juicy sub-bass, the vibrator doesn't activate and you feel like putting the headphone in a microwave.