Is 8.7hz too low for tonearm/cart resonance?

I'm no expert, but everything I've read over the years (and I've read a lot) indicates that the preferred range for tonearm/cartridge resonance is from 8 Hz to 11 Hz. So according to that, you should be okay. I'm not sure if your floor/footfall situation presents any problems.

-Bob

I cannot find the chart I saw where???anyway, the range is below 20Hz.. too close to 20Hz or over and you will pick it up in the signal and amplfy it.. very bad. So stay well below 20Hz. Then you want it well above walking, footfalls etc, and that stuff is under 6Hz if I remember. so you want it over 6Hz. The median is like 12Hz, but a range in there is fine.
So if you are nearer the low end, I would want a good isolation of TT from floor.
(Just a note, if your closer to 20Hz then you may need a 'rumble filter" in the signal chain.)

8-11hz is optimal, you're fine.

If you know the effective mass of your tonearm, you can go to cartridgedb-dot-com and double check everything with the cartridge resonance evaluator there.