If you guys want to see something wild - check out these 2 video clips I made a couple years ago, with a VPI Aries 3, stylus in groove (at rest), and system on with volume set to "loud" listening level. This was my "energetic" problem room (small office).
https://imgur.com/a/HMASPUi
The 1st video shows extreme excitation at ~ 100-ish Hz from lightly tapping the shelf surface the TT sits on. It’s literally like a drum. Laptop speakers won’t reproduce this frequency; you need headphones or desktop speakers. And turn the video volume up. I could absolutely hear this frequency creep during playback, from feedback. It sounds remarkably like a ground hum, except that it rises as you increase volume. At a certain point, it can runaway (very bad, had to keep a finger on mute).
2nd video shows a greatly reduced effect, even as I slap the platform much harder! And it’s at the same system volume level. This is thanks to the metal 10.5i arm and HW-40 feet (squishy foam - with hockey pucks for spacers), versus the 3D arm and Classic Signature feet (hard - with Herbie’s giant fat dots for spacers). I should have made a video with the same feet, to show that much of the blame actually goes to the 3D arm. Fatboy arms were a similar story.
That’s a not-cheap CMS Sotto Voce rack and $2K Platinum shelf. Completely useless at this frequency! In the end, I think the rack’s architecture, table plinth design, and 3D tonearm are all to blame. And the Avenger Reference did nothing to help here. I thought its tripod plinth design might help, but it didn’t. Might have a video of that floating around somewhere.
Anyways, the Clearaudio Innovation compact had NO problems at 100Hz, but you had to watch subsonic feedback for woofer flapping (dangerous) - that’s from the float bearing IMO (again, the Master adds enough mass it’s less problematic). You can put this on a Townshend spring platform and it helps a lot! The problem with the VPIs, is their size makes it hard to fit onto a Townshend if you’re space constrained. I guess I should’ve tried the pods.
And the SOTA Cosmos, of course that does fine no problems :)
If I could re-do the rack choice I’d get an Adona with the cross-bracing. I think rigidity - in all directions - is a rack’s #1 job.