This is possibly the coolest music video ever made!
The outgoing Commander of the ISS singing "Space Oddity". In space.
(project description and photo from a customer)
This type of system uses a specially tuned 10" passive radiator to augment the bass response of the 8" woofer, as exemplified by the HUMAN 81-10, and the Genesis II, 2+, and 20. Other than this extra part and box volume being much more critical, it is essentially the same speaker as the model 81 project.
The crossover used by EPI and HUMAN is just a single ten microfarad capacitor (I'd recommend using a high quality film type capacitor) in series with the tweeter. The Genesis II and 2+ also added a shunt coil of 0.47 mH, and the Genesis 20 used 8.2 uF shunted by a 0.9 mH choke coil - these "second order" networks are intended to decrease the power "seen" by the tweeter below the roll off frequency. Since this comes with a penalty in the linearity of the phase response, I prefer to use the single capacitor design myself.
Interior dimensions in inches, volume in cubic feet:
Stock bracing: None (except HUMAN models). I recommend adding at least one brace front to rear at the point between the woofer and tweeter cutouts, and likewise between the woofer and passive.
Driver position: Offset from center of cabinet face, tweeter a different distance from the top than the sides, drivers as close together as practical.
What you will need from me to build them:
The HUMAN 81 Kit includes:
2 PRO 005 woofers