The Extra Stimulus Twin Iso 8
The "Extra Stimulus Twin Iso 8" is a four way ported system with four 8" woofers in dual isobaric pairs, a 5" mid bass in a sealed sub-enclosure, a 3" dome midrange, and a 1" titanium dome tweeter.
The resonant frequency of this system is 21.75 Hz.
The estimated -3 dB point is at 19 Hz.
The power rating is somewhere around 150 watts each.
The aproximate efficiency of this system is 90 dB SPL at 1 watt at 1 meter.
I would estimate the total cost of the stereo pair, all materials included,
to be less than $600 (US), and an awful lot of work.