Vibration control has been a big thing with me going back to the early 90's. Recently, over the last few months, I've been experimenting with various types of springs and comparing a number of them. The whole story, more or less, is laid out in Millercarbon's Mega Vibration Control Journey https://forum.audiogon.com/discussions/millercarbon-s-mega-vibration-control-journey
Spoiler Alert: Millercarbon has added springs to his Mass/Stiffness/Damping approach to vibration control.
For more on the story of springs check out noromance's thread here: https://forum.audiogon.com/discussions/springs-under-turntable?highlight=springs%2Bunder%2Bturntable
Ordinary eBay springs were working great under my amp and speakers. The Nobsound springs were working great under my turntable. Especially good for the money, I thought. Until some kind of really bad feedback/resonance problem came up- a powerful rumbling that at first sounded like it might be turntable bearing failure.
Eventually the problem was chased down to a lack of spring damping. Basically, once a certain frequency got going it would resonate, and quite loud. Even the slightest damping would eliminate it. But this got me thinking. Surely this was only the most obvious form of resonance. There's no damping on any of these springs. Its only just by coincidence this happened to be so obvious. Plenty of others using the same springs without any problems.
Still, it got me thinking. There has to be some damping or the spring will just bounce, maybe even getting into a resonant mode like my turntable was doing. There has to be some damping. But not much, or it stops being a spring. The trick is to somehow get the isolating bounce of the spring combined with enough damping to eliminate resonant feedback. Kind of like on a car, you need damping for control in curves but not too much or you won't have a smooth ride. Townshend Seismic Pods are made with 0.16 damping factor. This finally convinced me to give them a try.
Seismic Pods are a spring wrapped in a rubber bellows. As the springs compress it causes the bellows to force air through a small hole. The bellows and hole are engineered to allow free movement for isolation of very small vibrations, yet while still providing adequate damping for avoiding problems with resonance. Seismic pods are sized by component weight. In my case both my amp and turntable are right about 75lbs.
The Townshend Pods are a good deal more user-friendly than Nobsound or my DIY springs. They are covered top and bottom with a thin felt that made them easy to slide around and adjust. The threaded top turns easily even under load, making leveling easy and precise. No more shims! My turntable was more level than ever before- and faster!
The sound was at first listen just a wee bit underwhelming. Perhaps my expectations were set a bit too high? The longer I listened though the more apparent it became there was a whole lot more refinement now. Instrumental texture and tonality were rendered a lot more clearly- string guitar sounding more believably string guitar-like. Certain bass lines were now more smooth and natural than before. By before I mean before the other springs, before BDR as well. Smoother and more natural than ever. There was a noticeable improvement in low extension, particularly in terms of slam and at the lowest frequencies, but the top end, other than losing a bit of grain and becoming a bit more liquid, was little changed.
All together a very nice improvement, if one that left me scratching my head a bit wondering why it wasn't even better still. This after all is a turntable. What one might think would be the best place to show off what the Pods can do. To be sure, there was real significant improvement in tone and texture, with a lot more detail coming through and in a lot more natural sounding way. Maybe I was just expecting too much?
Next they went under the Melody. The turntable experience had reset expectations for the integrated amp, which may be why I was so blown away. Where the Pods under the turntable were all refinement, here they were all balls! Dynamics! Extension! Now you're talking! It was like the experience with the Tekton Moabs, suddenly the music just comes alive with incredible detail and yet in a very natural non-fatiguing way.
The talk from Townshend is this is due to the "very sensitive tube grid" which does I guess make sense. Electrons stream across, its a physical flow that of course vibrations will affect. Everyone is familiar with tube microphonics. The same only different, as they say.
Whatever the explanation the fact is the improvement is impressive. The sound was already good but now is even that much more alive. No downsides I have been able to identify, and the more I listen the more I like em.