Serowbot wrote on 06/21/12 at 10:10:11:360,... I put some spray in, expanding foam insulation,(sold for home wall outlet insulation)... in mine...
It is said to reduce harmonic oscillations without adding weight...
Very messy job though....
It expanded, all over the place...
...
Can't say if it did anything or not.... didn't try the bar hollow...
... but the theory sounded good...
LOL, I know. I've used that stuff before and it's like attack of son of flubber or something.
I've been doing some research and found that various "fillers" don't suppress as much as they move the resonant frequency up or down the scale. Completely empty, the bars are like a bell with a natural resonance (in fact they ring if you hang them up and hit them with a wrench). If their natural ring or any harmonic is close to the bike's vibration at a given rpm, then you will get a combining amplification factor. In any case, if I could just rid the primary vibration at hiway speeds of 60..70mph (rpm?) then I'd be semi-pleased.
I've looked at various things like mixing lead shot with silicon gorp, or inserting hollow lead round stock with a bolt thru it to expand and pull it tight inside the tubing. There are also several companies who make "tuned mass dampers" that vibrate at the same frequency, but opposite phase (i.e., counter vibrate).
I even came up with a design with a microcontroller that reduces oscillations dynamically at any rpm using counter vibration feedback. The problem is you have to drill a hole in your bars and run 12V inside, and the gadget also wears out eventually.