crappy photo but i'm not ed weston. so here is the back. i added foam and felt to the panels as an experiment to see if diffration and resonance effects would be decreased. not sure if it makes any difference. the midwoofer fires into an open-backed chamber filled with acoustastuff in order to absorb the high frequencies but let the lows pass through. a dipole supposedly produces better bass because room interactions are lessened but side wave cancellation and also the rear energy of the woofer is no longer reflected back to the driver. a massive crossover is necessary to equalize the thing. that is why most dipoles are active.