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

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.

Headphones are small and can go down to 20hz.  They're pretty small speakers.

atmasphere
3 dB (down) 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.

actually decibels are already logarithmic; hearing is not on a logarithmic scale. the microphone used to measure the SPL is a listening device and measures what the human ear actually hears. If the SPL is 3 dB down at 20 Hz then you will hear 20 Hz as half as loud as any frequency that is measured as 0 dB. If 20 Hz was found to be - 6 dB it would be 1/4 as loud as a frequency at 0 dB.