Plenty of organs go below 20Hz though, and even an otherwise good sound system starts to struggle around 40Hz if it's not built specifically for playing such notes.

Dumb question but how is the piano capable of generating these frequencies? I thought the strings couldn't get nearly long enough and the low frequencies that you heard from piano were just psychoacoustics.

The bass strings are wound with copper wire so that the mass is much higher and the resonant frequency much lower.

The amount of space needed for a certain frequency in air is different to the length needed for that same frequency in a wire.

It might help to see the formula, which is:

Frequency = sqrt(tension/(mass / length)) / (2 * length)

So length, tension, and mass are all factors. Modern upright pianos also string the bass strings diagonally to give them a bit of extra length.

I can almost imagine seeing the low bass string on the longest piano vibrating. The frequency is so low you can pick hear the peaks and valleys.