Good way to dampen tonearm?

If you want to dampen your tonearm, I suggest water.
But I'm pretty certain you want to damp your tone arm. If you use the foam, it's permanent, you won't get it out. It will work and would certainly make an excellent dielectric.

I suggest instead you try compressing a piece or two of polyurethane foam and sticking it in the tube. Or possibly those soft orange ear plugs available at Home Depot for pennies, or maybe you have some at work.

Now dry off that tonearm and get going, PS, adding water to the spray foam will make it expand even more. I strongly suggest the tonearm be dry.

loon

I think that is a very bad idea especially since this would be permanent. What if it sounded like crap? You would be buying a new arm.

DAP makes a foam that can be cleaned up with water, but the other stuff (Great Stuff?) is polyurethane based, it is very sticky, and you need something like acetone to clean up. It might attack the coating on your wire and will certainly expand out of the tube and make a mess that will be hard to clean up. You will also have to compensate for the extra weight.

While I assume it is a dielectric (insulator) it's dielectric properties will be different than the one it replaces (air) and may alter the sound.

You will also be changing the effective mass and resonant frequency of the tone arm and your cartridge may no longer be a good match for it. Check out http://www.gcaudio.com/resources/howtos/tonearmcartridge.html

If you want to experiment I would go with the other ideas above that are easily reversed.

BTW dampen was used correctly in the original post.

damp·en
v. damp·ened, damp·en·ing, damp·ens
v.tr.
1. To make damp.
2. To deaden, restrain, or depress:
3. To soundproof.

Dampen is a verb and was used correctly. Damp is a noun or adjective so it is used incorrectly in the phrase "damp your tone arm."

The real issue is your adding quite a bit of weight, especially with Water, you might not have enough counterweight, especially if your cartridge is a higher gram cartridge. Beyond that yeah permanancy of it is dangerous, and how would you really Seal water into a tonearm safely? I sure would not want it coming out on my equipment or record labels. By the way they make Tonearm damping Gel's of some type, and at least this would be a gel not hardend foam or runny water which you could still pull wiring and stuff thru I would guess, I think KAB turntables(?) somebody like that sells it.

There are a couple of inexpensive ways to dampen your tone arm that are easily reversable. One is to wrap the arm tube with plumbers teflon tape. Simply wrap the entire arm, or alternately, two or three spots with multiple layers of the tape. Another is to purchase some shrink tubes from Radio Shack. These are 4" long plastic tubes that can be slipped over the arm tube and shrunk snugly onto the armtube by gently heating them with a hair dryer. Either of these techniques will have a dampening effect and you can decide whether or not you like them. If not, simply remove them and you'll only be out a few dollars, at most.
Finally, Herbies Audio has HAL-O JR dampers that might work as well and if you don't like them just return them for a refund: http://herbiesaudiolab.home.att.net/jr.htm

Why not dampen it with something from the outside instead of the inside? I remember a local audio dealer that did this with a Well Tempered table (not sure of the arm). He had it wrapped just as you would re-wrap a tennis grip. It was a rubbery material maybe 3 millimeters wide. I'm not sure what it was exactly, but this is certainly an idea to explore. Good luck!