Servo feedback subwoofer

hi its me again bothering u with my audio oriented questions
I just saw an old interview of Bruce Hall from Velodyne Acoustics talking about their servo feedback subwoofer. And i went like . He said they're using this in sealed boxes. I'm wondering could this be used in ported boxes... And instead of an accelerometer could one use a good mic lets say for freq above 40 Hz?
P.S. i hope i'm posting where i should

I'm gonna guess a mic is probably not a good feedback provider. I'd say use a passive voice coil with a magnet on the servo drive.