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

Kii is interesting in that it takes a unique approach

Head/earphones don't count.

^interesting yes, but if I'm missing something please point it out to me; where are the specs, measurements, tolerances? Without which, I don't think they can qualify. 

Specs?  Did not see any of those. 

from the manual

http://www.kii.audio/phocadownload/Kii_THREE_manual_online_EN.pdf

Technical Specifications:
Compact DSP controlled monitor speaker
4x 6.5” woofer, 1x5” midrange, 1” waveguided tweeter, all individually driven
Amplification: 6x250W full-custom Ncore
Active Wave Focusing crossover filter
Frequency response: 20Hz to 25kHz +/- 0.5dB
Phase response: minimum (best possible time coherence).
Long term SPL(*): 105dB
Short term SPL(*): 110dB
Peak SPL: 115dB
Controlled Directivity: 4.8dB (80Hz - 1kHz, slowly rising thereafter)
Size: 20x40x40cm, 8”x16”x16” (WxHxD)
Weight: 15kg (33lbs)
Inputs: Analogue, AES/EBU
Selectable correction for free-standing, near wall or in corner

I think we have a winner!
Incredible!