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RE: Have some issues getting his calc to work...

Posted by flood2 on May 10, 2022 at 13:39:54:
My preference mirrors yours - my best sounding cartridge matches give around 9Hz to 10Hz (by measurement) in an SL1200 arm with Jelco HS20/25 (12g mass). The oft quoted 8 to 12 Hz range is just a recommendation that clears the warp frequency range and gives a sufficient margin below 20Hz. Getting too close to the audible range gives a "flutter" effect on low frequency test tones around 20Hz. I had some very low compliance Stanton styli that gave a resonance around 17Hz (likely duds!!) for which I was able to verify these effects for myself.

The LF resonance modulates the VTA and SRA. If you do spectral analysis you see sidebands on either side of the groove signal frequency components - the higher the Q the higher amplitude of the sidebands. Not only does this contribute to signal colouration, but the instability of the cantilever increases the IMD and can degrade tracking ability very significantly.

Knowing the actual effective mass of the arm requires specific knowledge of all masses (i.e cartridge/headshell/fixings/counterweight) plus the VTF set. This is almost never given so the published specification can be a little misleading when comparing calculations and objective measurement with a test disc.
For example with the TA-110 arm, Ortofon quote the effective mass of the arm as 3.5g (without headshell)....then tell you the headshell mass is 15.5g. The missing information is the fixing mass and the cartridge mass and the final counterweight position for the VTF you require.

One has to make some really big changes to headshell and counterweight masses to make any difference, hence why most people find they don't have a problem when they try and mate their cartridge despite the calculations telling them otherwise. To compensate for the higher mass of the Jelco HS20/25, I added a suitable auxiliary counter weight which shifts the main counterweight closer to the arm bearing which improves things with higher compliance cartridges.
You could experiment with that.