This has resolved for me the question of whether to upgrade from my 350 (w/500/600 driver) to a 500. I did SPL readings down to 16 Hz and it was actually a little above the flatline (which I set at 80 dB). It's pushing well!

---- A Woofer in Tweeter's Clothing... M60s, VP150, QS8s, EP350 Onkyo TX-SR702, Denon DVD-3910