Could not agree more with Eldartford. The same can be said of tuned ports to extend frequency range...often the results are less perfect than can be achieved with a separate dedicated driver (usually from a subwoofer) just for the low end. In the end it is often about compromise. Getting transducers to cover a broader frequency range helps in some sense by eliminating the challenges of cross overs but the downside is that the optimum freq range for that particular driver (size/material) may be exceeded and this usually results in more THD/IMD distortion and significantly less dynamic range.
Discrete transducers appropriately sized for their frequency range and precisely integrated using separate active electronics for each transducer is a solution that some speaker manufacturer's have adopted. A system of this type with large dynamic range and low distortion requires a four way system: subwoofer for 20 to 60 Hz, Woofer for 60 to 400 Hz, Mid range from 400 to 3000 Hz and tweeter from 3K to 20K Hz. The drawback of a system using more transducers and discrete active electronics is higher cost. The advantage is relatively low distortion and high dyanmic range (for a speaker). Nevertheless, harmonic distortion is in the 0.3% range, which is still hundreds of times more distortion than typical digital source and SS circuits.