What are the smallest speakers that are clean and flat down to 20hz?

Its not absurd at all. Its a well documented fact.

Turn the volume up and things are better but still far from flat.

Equalization is the only practical solution if one truly cares beyond that.

It helps to manage expectations though to realize and understand that what we hear is not the same as what measures as flat.

If the speaker rolls off at extreme frequencies, then we hear even less.    

The ability to not roll off at frequency extremes and make things even worse is what separates the men from the boys.

Compensating with equalization is then analogous to using performance enhancing drugs.  that is assuming the amp and speakers can handle it.  That's a different story.   if they can't,  then the results will surely not be good.

Wow, those Ohm speakers remind me of my old BIC Soundspan 600 speakers. 

Hartley 18" and/or 24" subs might be flat to 20 Hz. Everything else is a pig in a poke.

Mapman
Compensating with equalization is then analogous to using performance enhancing drugs. that is assuming the amp and speakers can handle it.

imo - The smart speaker manufacturer realizes most rooms do not support 20 hz, and builds this EQ into the speakers design for the full range models. The speakers can handle it if they were designed to. In some cases this changes the load the speaker is looking for and actually makes them easier for the amp. I can give an example if you like.