The bars don't function as tuning forks. I tried something like this years ago with a piece of all-thread and some brackets that were bolted to the mirror holes. It didn't do a thing. If this thing works it is because it is absorbing some the vibration.
I was Kinda wondering that. Actualy that was the reason that I was using the soft rubber tips. Do do recall how much torque you tightened your all-thread to?
All I know is while riding; if I press hard on the end of my bars, the buzz goes away.
Either way it works, and its worth looking into. I'm to damn cheap...errrrr I mean frugal for Heli-bars and the such. I was just looking for a cheap yet affective approach to reduce the "buzz of death"