Vibraplane: Should it be loaded close to limit?

Palasr, doesn't the top plate have three mounting bolts? I wonder if a different material could be used.

Dan,

The surface has no holes; it's an option. I did think of putting my sandbox directly on the VP, but it was too heavy (around 190 lbs (!)) - we each stood on a separate bathroom scale, and aggregated the results, minus our respective weights. A funny sight to be sure.

I can report some very early impressions. I set up the Vibraplane under my TT with no intermediate slab to preload the unit. The improved isolation results in a more articulate bass with more weight and, subjectively, more extension. There is a more silent (blacker) background and overall drop in noise floor which improves dynamics and very low level detail retrieval. I'm hearing spacial cues which I did not notice before as well as clearer relationships between individual instruments further back in the soundstage. In fact, I didn't really have much depth to the soundstage before. Plucked violins in the background providing a foundation for solo mandolins in the foreground for example never sounded this convincing. They are separate in space, articulate and clearly distinct. Finally, I can play the system louder without it starting to break up during complex and energetic passages.

It did take some time to fiddle with leveling the unit using the hand pump on my passive unit and I can see how the active model with compressor would be more convenient. I don't notice any chatter between my TT and the top plate of my VP as the SME TT has rubber footers and notice no such stridency in the upper midrange.

I would add that I find the isolation to be cumulative. I bought my first Townshend Seismic Sink for under my TT and when I bought a second one, I put the first one under my pre amp. Now my second Townshend is under my phono amp. I did listen to these in stages and each addition improved the sound, and the VP seems to be more effective than the TSS.

After I live with the VP for a while, I will start to experiment with different heights and preloading.

Great feedback, guys! Richard and Peter, I'll be interested to hear your thoughts on auto load leveling and the lack thereof as you guys get more time with these units. I'm interested to know how well each unit holds pressure, and how often they need to be leveled in normal use. A passive would certainly be easier and cheaper to build.

These commercial air springs have stiffer side walls which give them an advantage over simple air bladders.

Richard, can you see a way to add a valve in the airline just before the Vibraplane? I assume there is a pressure gauge in the vibraplane. Closing that after pressurizing may tell you if the slow leak is in the unit or before. Does it bleed off air normally as part of the leveling? I'm not sure the compressor running every 6 hours or so would be enough to build up moisture in the air lines. That is the only reason I would even think about how often it cycles. I also wonder if it could be sufficient to run one off of an air bottle in a closed system.

Don't laugh at the bathroom scale trick. We used to do that with our race cars to set the suspension. One scale under each wheel. Obviously, these were pretty light cars.

Dan,

Indeed the Vibraplane uses a type of air spring which I think contributes significantly to its excellent horizontal isolation; they are not mere bladders, or else I'd just do the inner tube trick and be done. The compressor has a regulator and moisture trap, and the Vibraplane has its own regulator valve as well. Alas, I traced the leak back to the unit itself, and not the air line(s) on or from the compressor. While I am uncertain if it's actually an air spring leaking or one of the leveling regulators (for lack of a better term) it still means having to flip it over to find out - soapy water at the ready. There's also a lot of air tubing running all over the place under there, so it could be that as well.

Needless to say, I'm going to have to return to the sandbox for a while until I can pin down the problem. Of course cajoling friends into helping one heft these things around usually takes a free dinner and plenty of beer...ah the lengths we go to for this hobby.