Musical instrument repair is clearly more complex than this—it's a skilled, improvisational profession that would probably welcome this kind of trick. I feel that, outside of Mega City One, those specialists just would not exist, their skills wouldn't be sustainable as a source of employment. That's the economic side of this—it's cool to come up with new techniques for instrument repair, but try being an instrument repairer in a city on the periphery. It's scary that this kind of (fairly mild) specialization is so precarious.
Made lots of these as a kid.
In my search I found this fascinating page on the physics of brass instruments. But this  is the best image I could find.
Does it rely on eddy currents in the steel ball? Wouldn't copper work much better in that case? Will the ball be large enough for eddy currents to be big enough to have much effect?
Now when the stop bar is struck by the mass, the magnet is violently moved away in a short amount of time. For a brief moment, the force is unbalanced, because the magnet has lost contact with the wall; only the ball is pushing on it.
The magnetic attraction may not in and of itself be strong, but the impulse is.
In physics, FΔt is called impulse. The impulse applied to an object changes its momentum: FΔt = Δmv.
If we keep the Δmv the same, but decrease Δt, we can raise the F.