Anybody have ant thoughts re using 2 Herbie's tube dampers on 1 tube?

I'm already using Herbie's UltraSonic SS on the 6SN7s in my amp. I'm definitely happy and believe they make a positive difference. I've noticed that in some pictures of a number of tube amps that some folks are using more than one of the "rubber" style dampers on their tubes. Does anyone have any ideas?
Two balance out vibrations the same way holding anything in two places does. 
However test, listen and see.
But first, try the tubes again without dampers to be sure you weren't just fooling yourself the first time. I prefer no damping. 
More than 1 will deaden and over damp the tube.Herbie are the best because they don't over damp like all the others.
its all trial and error ya know
Interesting question...I use one on each tube in my pre. I never thought about using more than one.
remember for any signal tube, what we are trying to do is to MANAGE microphony, not eliminate it
Save your money and get these, not too tight just a snug fit, measure the diameter of your small and big tubes and reduce it by 2mm for the ID of the o-rings needed, for them

They are high temp very high quality silicone o-rings, for industrial purposes. They stop the thin glass of todays cheaper Chinese/Russian tube from ringing, they WILL NOT! stop a faulty tube that has gone microphonic, neither will any other tube damper. 

BTW!!! There is no such thing as overdamping the glass envelope of a tube

Cheers George
Glad you said it, @georgehifi. An '"overdamped" tube glass envelope is the same as an overdamped loudspeaker enclosure: an oxymoron. Both should be as non-resonant as is reasonably possible to make them. The cases of electronics as well, for that matter. And turntables, tonearms, and phono cartridges, and the walls, floors, and ceilings of listening rooms.
Looks like we have another division of opinion! You can hear over-damping. It dries out the sound and dulls the music. Like everything in audio, it's mainly down to personal preference. 
I’ve used the same silicone O-rings as George (but- from McMaster-Carr), for decades.      Also agree (from my personal perspective); there’s no such thing as over-damping resonances.      I consider anything that adds or subtracts anything, from an original signal, as distortion or coloration.      Then again, when I had my shoppe; I catered to all tastes/preferences.      This is definitely one of those try-it-and-see-for-yourself situations.      iow: EXPERIMENT!

Damping is the absorption and (hopefully) dissipation of mechanical energy (vibrations). I don't know why one would want to leave the glass envelopes of his tubes free to "ring". Of course, that assumes the glass actually IS ringing. If it's not, it doesn't need damping, right? How can the glass be "over-damped"? Once the ringing is eliminated, it can't be reduced any further.

If one tube damper stops all ringing, obviously no more are needed. If that damper leaves some ringing, why wouldn't you want to add more damping? That's just like bracing a loudspeaker enclosure well enough to reduce it's flexing, but stopping short of eliminating it well enough to reduce the resulting resonance to below audibility.

I really like the enclosure design Albert Von Schweikert came up with a few years back: each panel is constructed of multiple layers (three, I believe), each layer a different material (to "scatter" the resonant frequencies of the combined layers), and constrained-layer damping is applied between each pair of layers.

An opposite approach is that taken by some of the UK loudspeaker companies, who intentionally leave their enclosures under-damped, using the resulting resonance to create sound output. The problem is, once an unbraced enclosure wall starts ringing in response to a vibration fed to it (music), that ringing is not necessarily going to stop to stop when the music does. Not good! Danny Richie of GR Research is constantly measuring speakers sent him, and the waterfall plot of many reveal LOTS of uncontrolled enclosure resonance (ringing). One reason dipoles sound so different from boxed speakers is the lack of that enclosure resonance.

Wow, I just love this hobby. Never thought that my question would precipitate such a lively discussion. Thank you all for the very provocative input.

I'm in the "you can't over damp" group and the "you must experiment" camp.

Thanks and best regards to all. Please stay safe!!
Just remember the basic Audiogon Forum rule: the more microscopic the topic (e.g. orientation of after-market fuse in fuse socket) the more ferocious the debate.

(Like any good rule, this has a few exceptions.)