I've never even HEARD of a STC rating, so take this with a grain of salt:

90dB of a 1KHz tone is not going to annoy the neighbors nearly as much as 90dB of a 20Hz tone....

I know that's obvious, but I wonder how likely that STC "spec" takes subsonic frequencies into play?

::::::: No disrespect to Axiom, but my favorite woofer is my yellow lab :::::::