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

Mapman,

Even if you were to find 2 ch speakers or subs of any size that were flat down to 1hz +/- 0 dbs, the unfortunate truth is that the physics of acoustical sound wave propagation is going to ensure you don't perceive flat bass response in your room, assuming your room has walls, a floor and a ceiling. As long as your spkrs/subs are located along your front wall, there will be uneven bass response in the room; specific spots in your room that bass is exaggerated and specific spots that bass is diminished and even nonexistent.    

Sorry to rain on your parade but I've discovered there is a good solution, called a Distributed Array Bass System, that works amazingly well. These systems are sold under various names (SWARM, DEBRA, etc.).  I have used the DEBRA system for about a year now and I'm completely satisfied with the results. I started an Audiogon thread in June of this year that goes into more detail and requested input from other users (there doesn't seem to be many Audiogon users that employ this bass system).  Here's a link if you're interested: 

https://forum.audiogon.com/discussions/anybody-else-using-a-distributed-array-sub-system

You can also google "distributed bass array system" that will list multiple sources of independent info, including sites on the specifics of how it works, white papers that discuss the theories behind it with empirical data as well as current sellers of these systems.

I should mention that I was initially very skeptical due mainly to the cost ($4,000) and whether it actually worked as well as claimed.  It took months of emails and phone discussions with the seller before I decided to give it a try.  I am now very grateful I bought this system that works so exceptionally well for both my 2 ch music (especially on high-res music files that are thankfully without 'loudness wars' dynamic limitations) and HT. This system has given me solid, deep and tuneful bass that sounds equally good from all 6 seats in my 23' x 18' room.  It is somewhat expensive (I rationalized it by comparing it to the cost of 2 high-end powered subs I was previously considering) and it takes the better part of a day to properly setup in a rather detailed and extensive process.  But I now consider it a bargain and realize the extensive setup process is critical for good results.  
Lastly  a disclaimer, I have absolutely no affiliations, financial or otherwise, in the development or sales of these systems.

Just a very satisfied customer,
    Tim 
 

Good stuff folks, keep it coming.

noble I just want to know the small speakers capable of it in a typical room.

I’m familiar with the swarm approach. That’s probably the most effective approach in the end if done right I’d say..

30hz isn’t bad as long as the size is small accordingly. I could probably live with that. But 20hz or even lower maybe is best.

I really mean  the speaker does not roll off much or at at all at 20hz in a typical room.  How flat it is or not will largely depend on room acoustics from there right?  If it can only be done in a smaller room fine, just say so.  I'd expect one capable of it in a smaller room to be physically smaller than one for a larger room.

^That's why speakers should be anechoic spec'd. It gives us a standard neutral base line. Now you just need to provide us with your specific criterion, so the equation can be completed.   +/- 3 dB seems to be fairly standard, though better is well, better. :-)

3 dB at 20 Hz which is half as loud at 20 Hz

To be audibly half as loud is usually considered 6-10db on account of the ear being on a logarithmic scale.

I really mean  the speaker does not roll off much or at at all at 20hz in a typical room.  How flat it is or not will largely depend on room acoustics from there right?  If it can only be done in a smaller room fine, just say so.  

The room will have some influence certainly, but if you really want 20Hz response **with any sort of dynamic range**, its not going to be a small speaker.  Note emphasis.