Eminent Technology ET-2 Tonearm Owners

TEST FOR STRUCTURE FEEDBACK ……. Start jumping up and down right beside your TT…….

Hi Ct,

The most extremely test of this sort that I have seen was that, while following your initial settings, instead of jumping around the TT, you kick on its stand! :-) 

It was performed on a Rockport Sirius III at the agent, and yes, it was pretty much silent from the speakers! That stand was actually an OEM pneumatic table by TMC, and I am using a similar one under my Capella II. Unless you kick it hard enough that the whole stand / TT assembly (roughly 400-500 lbs.) moves over the floor, you can hardly hear any thumping from the speaker indeed!

Hi Dover,

You have mentioned that too high a horizontal effective mass would result in a raised bass response by 6-12db. So, in what frequency range are we talking about (the Fr at below 12Hz?)?

I just wonder if the high horizontal effective mass is the only consideration here, and whether other factors, such as the design of the air-bearing, would make a considerable difference in the outcome. In short, does that only apply to the ET design, or also to the Rockport and Kuzma etc?

I asked because my Rockport 6000, already has a high horizontal effective mass of 80g (with the lightest counterweight, and excluding the cartridge), but yet MF found it lacking in the bass! The upgraded 7000 and Sirius III arms added even more mass to “cure” this problem!

Not meant to be argumentative, just want to learn more! Thanks!

The most extremely test of this sort that I have seen was that, while following your initial settings, instead of jumping around the TT, you kick on its stand!

This is not a test for Structure-Borne Feedback.
It merely places a Dynamic (hitting) sound source into a structure.
I have never seen a scientic correlation between 'Impact' sound sources and Air or Structure Borne sound sources?
It is like the ubiquitous "Boink Test" that some audio reviewers used to do........tapping on the plinths of their turntables to see how 'immune' the turntable is feedback?
Chris' test of jumping on the floor around the turntable is a little more viable as it transfers the impact-induced source into Structure-Borne feedback within the floor........ however the form of that feedback is quite different to that which our systems are normally subjected.
Any suspended floor system (timber or steel-framed or reinforced concrete) will be subjected to Structure-Borne Feedback because of the stresses and deflections caused by the structural spans.....as well as the materials used in the floor construction.
These stresses result in subsonic low-frequency Structure-Borne feedback which passes easily into equipment racks, support stands and into the turntable plinths sitting upon these racks/stands.
That's why a wall-mounted turntable shelf is the best way to minimise this.

These stresses result in subsonic low-frequency Structure-Borne feedback which passes easily into equipment racks, support stands and into the turntable plinths sitting upon these racks/stands.

Hi Halcro,

Thanks for the information! So, any idea what is the frequency range of these structure-borne feedback?

Thanks!

Hi Thekong,
In a suspended reinforced concrete slab......there can be frequencies from 5-10Hz and higher.
In a suspended timber-framed floor they could get up to 10-16 Hz but would not normally get as low as the concrete.
Of course....the 'creaking' we can often hear in suspended floor structures as they 'move' whilst we are in bed at nights......are of a far higher frequency.
It's really the very low frequencies doing the damage as Structure-Borne Feedback as they are indicative of 'movement' within the floor structure.

Hi Halcro,

Thanks for the information again! As I can’t use wall mount in my room, I have never experience its effectiveness!

My room has suspended concrete floor. According to the specification, the pneumatic table could isolate up to 85-90% of the vibration at 5Hz, and 97% at 10 Hz, it has worked out very well for me! I certainly could hear the improvement in background blackness with its use!

Thanks!