Plinth against microphonic issues with sensitive tubes

[fritzthecat]

I had some problems regarding vibrations with coming from the wooden floor in my house (gonna support it from the cellar with some wooden bars to avoid the whole flor from swining but still there will be some impact sound from walking around. So I built a prototype of a air suspended base to get rid of this. Does anyone have experience with experiments like this?

At the moment two Silvercore 833 mono power amps plus one Kaiju are sitting on the air suspended top board and it is almost gone - overall the sound is much more stable and on the spot now - bass won dramatically and the mids as well.

Actually I just took four small tubes for bicycle tyres and connected them via some pneumatic hoses via their valves - built a frame underneath the top board of my rack (200x50x2,5 cm (actually 2 times 2,5 cm as I had to use two massive oak tree boards because of the weight of the amps that made a single oak board bend after a while because of the uneven weitht distribution - different amps = different weights) where the bicycle tubes fit in - then just pump the right amout of air to get enough pressure to elevate the top board about 5 mm while the amps are sitting on top and that's it.

I thought the trick is to have the same pressure all over (just realised that this is not working very well - the top board of my HiFi rack is about 2 meters broad - so the different weights of the amps even makes the massive oak bend makes it bend after a while so the whole thing started to look like a banana (but still worked fine - which actually is amazing). So what I did is to divide it in to two circle runs - one connecting the outer tubes (where the heavier Silvercores are sitting on top) the other connecting the inner tubes (where the less hevy Kaiju sits) and now there is no more bending effect - I was very surprised that a massive board consisting of two massive oak boards (each one inch thick - makes a two inch tick board (!) bends under the weight - but it is what it is...

In the future I will try single bases for each amp because the Silvercores are much heavier than the Kaiju and I am already researching for air based bungees to make the thing look a bit more sophisticated.

Does anyone in here have experience regarding experiments like this? I am researching for smaller air springs and already found some stuff that looks good...;o)

Picture: as you see, the top board is elevated from the base and one can see one of the bicylcle tubes - looks adventurous (it's just a prototype or an experiment) but it works. In the future I would like to use massive slate boards and pneumatic bungees for this and will try to calculate resonance frequencies including the amps weight...

[howardnair]

Fritz. You need a frame to support the oak or the slate slabs whether you air suspend it or hang it from bungees  Ask a local carpenter or builder for advice  it may make more sense to support the floor properly vs air/ bungee support system   Regardless of air support or hanging the floor and the house are still going to shake

[Natural Sound]

I went with a box filled with fine sand. On top of that is a heavy maple slab that "floats" on the sand. My home sits on a concrete slab so there is no vibration from below. When I had a house with a crawl space underneath I wall mounted a very solid shelf system that provided ample isolation for my turntable and tube gear. I mention this because in your situation wall mounting may very well be a better solution.

[Doc B.]

When I was at Berkeley there was a hologram making setup in the senior physics lab. It was the same kind of setup scaled up, a 4'x8' sand filled box floating on car tire inner tubes. The way you measured the settling time of vibration getting through was to set up a Michelson interferometer on the box that projected on the wall, and calculate the average time for the fringes to settle from blur to sharpness. The average spacing between the blurring events determined how long an exposure you could make of the photographic plate. It was quite effective. Presumably one could do the same for any isolation platform if they were really trying to make it perfect. I think otherwise the optimal result would have to be based upon stomping around and playing with mass and pressure to find the best damping. Bigger is going to be better.

[fritzthecat]

On Saturday I'll see the metal dealer in my confidence to figure out what kind of tubes he has to offer that could work as a supporting frame. I thought of filling the tubes (after welding of course...;o) with a mix of fine dry sand and shotgun lead. To fill them I'll cut some threads I can easily close with lets say M8 screws. Combining these with massive slate platforms for the amps it will be a quite heavy and very stable thing. The wall thickness of the tubes should be 3 to 4 milimeters. I found some air spring systems being used for truck driver seats that might do the job - going to research further.