Tom the air tube suspension is widely used currently, like Aricci suspense rack, Townshend sinks, and bright star air mass etc. Of course big bucks buys you vibraplane where shelf rides on a cushion of air, no tube needed. Never tried fluids in a tube, as you describe can be a challenge to perform, glad the results worked good for you. I have some fear of using water tube in my system because it is left on all the time, and if I am at work and tube leaks I could have nasty surprise when I get home, at least I know air is perfectly safe.
Tom_nice - I could be wrong, but it is possible you are going round in a circle. Using air bladders at first comes like a breath of fresh air because the peakiness of structure-borne resonances is removed. But on the other hand, the sharpness of the outlines and of leading edges is diminished. Your use of fluids may be giving you a half-way house that may be ideal for you. I will have to try an oil-filled bladder now, darn it. But after trying bladders I have had more success by getting rid of the bladder and focus on reducing the peakiness of the structure I use. As to leakage problems, you can deal with this by sitting the bladder in a shallow leak-proof box, but my experience is that leaks of this nature start out being very slow ones.
Megasam, I knew already that air bladders are commercially used--isn't that implicit in my post? But thanks anyway for the information, even though for me it wasn't. Redkiwi, I've come to respect your expertise from other posts, but if "the sharpness of the outlines and of leading edges is diminished", I must have lost my ears. EVERYTHING is better! But try for yourself. I have my tubes in a shallow box, as I've said, and even a catastrophic leak would be easily contained--not like a rack, for example. If there's a downside to thickish oil in tubes, I haven't heard it yet.
I was just fishing Tom because I was interested - but it is you that has got me hooked now - I am going to have to try this oil trick. I found there was a "swimminess" or somesuch that I struggle to explain with bladders. When you say everything is better are you referring to bladders in general or the improvement of oil over air?
We had a tweak demonstration for our Audio Society this weekend, and I would have to say that the innertubes under all components made a noticable improvement in all of the demos, both for soundstaging and for the leading edge of transients. You have to play with the air pressure--it shouldn't be too high, or you start losing the benefits. One thing our demonstration also tried, which many of us liked, was the use of silicon in the tubes. Tom, Redkiwi, you might want to try something like that as well as oil (not car oil, you're right, it would degrade the rubber), which we also found to be beneficial.
Reprince - Which silicone were you using? I'd tay away from cyclomethicone as it is a) volatile and b) a very good solvent. Best to go for a medium low viscosity polydimethylsiloxane (25 to 100 centipoise). Not sure where/how you buy at retail, but GE Silicones and Dow Corning are the major US manufacturers. You cna probably buy it from Aldrich or Fisher chemical supply companies.
Alexc: The silicone that our host tried was "silicone shock oil", which he got from a radio control hobby shop for $3.50 a bottle. He was and is still experimenting with it; currently he used 45 viscosity (they went from 10-100, he got 45 because that was what they had the most of), he had put 6 bottles of the stuff into the tube, and he thinks it might be able to use 2-3 more bottles. The hard part of this is getting it into the tube, of course; he had created an injection device (this gentleman is very inventive), but I don't know if there's such a device widely available otherwise. I'll have him check to make sure it's not cyclomethicone; thanks for the warning.
I use large veterinarian syringes (without the needle) for filling my souvenir snowdomes. I wonder if these would work well. The tip (hole) could easily be made larger as they are made of plastic.
Reprince - With a viscosity of 45 cps, it isnt cyclomethicone (which is closer to 5 csk). You should be fine. Out of curiosity..how big a bottle do you get for $ 3.50. The "industrial price of the PDMS (what you bough) is about $ 2/lb. Cyclomethicone goes for about $ 3/lb
Alexc, it wasn't me that got the stuff, but I did see the bottle and it can't be more than 4-5 oz. My friend who has been doing these experiments thanks you for the sources on silicone. By the way, getting back to Tom's original thread, my friend told me that he had tried water in the tubes also, but, interestingly, didn't feel that it was an improvement over the tube filled with air, at least to his ears. His feeling is that if you can get something like an oil or a silicone into the tube that does not conduct sound or other vibrations as well as water or air do and can actually damp vibrations, it should be an improvement (as Tom noted with the oil); that's why he's experimenting with the silicone in combination with air. Any way you look at it, this is a good cheap tweak that really works, and it's interesting to see how it might be improved.