The specs of small drivers can have a low cutoff - my bedroom speakers have a pair of 5.25" mid-bass drivers and are flat in-room through 30Hz.
In practice it doesn't work.
SPL is purely a function of displacement and frequency. Displacement requirements quadruple for each octave you drop in frequency, meaning excursion increases 4-fold in a sealed system when you don't change the diameter.
Play with www.linkwitzlab.com/spl_max1.xls if you want.
This has a couple of problems
1. Physics prevent reaching reasonable SPL levels with small drivers outside a car or closet environment where you have up to 12dB of cabin gain below the fundamental resonance .
2. Excursion increases 4-fold with each octave lower if you don't change diameter. Distortion is a function of excursion. My 5.25" midranges (about equal to a 6.5" driver - they have more area, but will have less excursion) double at low frequencies - the harmonics are loud enough that you hear the higher tone. IM distortion (why old transistor amps sound bad) also increases. I never got good midrange performance from drivers <= 6.5" when bass notes were also present. Adding a sub-woofer with a 80Hz cross-over always cleaned up bass and midrange in music with a bassline. I now use an 8.5" midrange, 2 10" long-throw subwoofers per side for bass below 120Hz, and add a 14.5" subwoofer for theatrical tracks where the bass is really out of hand.
If you want small speakers use subwoofers too. You can have small boxes for WAF, small baffles for minimal difraction, place the midrange+highs for their best performance, and the sub-woofers for the flattest response at your listening position.
Many people find the best integration when crossing over an octave above ported speakers' F3 point (LR4 order electrical high and lowpass) or at sealed speaker's F3 point (2nd order butterworth high-pass, LR4 low-pass).
If you don't want sub-woofers and do want full-range music (symphonic, rock, jazz with an upright bass, etc.) you need 3-way speakers with a large bass driver.
