Hi Frogman/Raul - hope this helps a little. I needed the rehash. Let’s try to understand this better and hopefully in words that anyone reading this can understand.
So we know it’s a resonance, vibration hobby - playing records. As far as the tonearm/cartridge combination mechanics on their own - it’s a spring system, with a natural occurring frequency -Resonant Frequency. Thinking about a tuning fork helps. A stiff tuning fork resonates high. Like a stiff MC cart with its low compliance cantilever. A "less" stiff tuning fork resonates lower - like a less stiff MM high compliance cart.
This shiny piece of black vinyl record is not perfect as we know. Non-centered center holes that cause speed and other issues, warps, scratches..... but if we look closely when the record spins, surface irregularities exist. Bruce discusses this in the damping trough manual. These irregularities are not part of the cutting process, but the molding process in making the record. You can see the small ripples on the surface as the record turns. These ripples excite the "natural resonant frequency" of the tonearm/cart. combination being used.
We want these resonances (which are not in the recorded music) to remain well below 20 hz where we can’t hear them. When a tonearm and cart are badly matched - resonances will rise and could and do cause problems. if the system is resolving enough it will be heard.
Bruce did measurements and found most tonearm/cart combinations give rise to the frequency some as high as 8db with high Q. Ok this is technical. Applies to speakers also, and this number would not be tolerated there. Yet no one has ever discussed it with vinyl play. 8^0... Anyway, the result of this resonant rise, he called the "Effects" - and they can be subtle and sometimes not so subtle - reproduced on our systems.
The Effects can cause a phase shift. Put simply the time the low frequency signals come from the tonearm/cart, are slightly shifted from the mid-range frequencies within the audible range, and substantially shifted up to several periods of resonance. Bruce measured near perfect low frequency phase response when the original ET 2.0 was used with the damping trough.
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The first ET 2.0 with "aluminum" armwand came out when MM’s were popular. So.....1) aluminum armwand with 2) MM cartridge, and 3) single leaf spring. The three are a good match in resonant natural frequency. Then stiffer lower compliance higher resonant MC’s arrived, and the damping trough was introduced.
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TAKEN FROM THE DAMPING TROUGH MANUAL
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Please note that the tonearm now responds much more slowly due to fluid damping.
A low frequency sweep was performed twice on the tonearm, once without the damping trough and once with the damping trough. The cartridge used was of very low compliance and the tonearm was set up so that a high amplitude high Q resonance existed. The results of the test show a reduction in the amplitude of the resonance of about 8 dB (horizontal). Not shown is the vertical resonance which was 15Hz with this cartridge and was reduced about 2 dB.
https://photos.app.goo.gl/oWHujb7CygwLU8SC7****************************************
In due course Bruce introduced the larger bored out ET 2.5 (lower resonant frequency air bearing manifold) with Carbon Fiber and Magnesium armwands were introduced, along with the double and triple leaf (stiffer leaf) springs to deal with stiffer higher resonant MC. So - Likewise the ET 2.5 with Magnesium wand mated with double or triple leaf spring, mated to a high compliance MM is a bad match.
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The first ET 2, the 2.0 version. with "aluminum armwand", and low compliance MC cart produces higher resonances - and is a bad match. Frogman confirmed this with his findings here.
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There are folks on the ET2 thread that are using an ET 2.0 with aluminum wand and MC and single leaf spring, and do not have a damping trough. Most have made other mods - either to the headshell or armwand to compensate. So anything is possible but we really do need details on gear setup here, when people give their opinions. For it to be helpful to other people. This is not plug and play. Vinyl never was in the higher end.
Remember we have no idea what lies downstream of the turntable in peoples homes and how the rest of the audio chain matches up to what is before. This helps to explain the infinite opinions on this forum.
This link in the ET2 Tonearm Owners thread, shows the setup to be followed for MM and MC carts - endorsed by BruceThigpen.
We called it one of the yellow sticky guidelines
https://forum.audiogon.com/discussions/eminent-technology-et-2-tonearm-owners/post?highlight=yellow%...
