ronboco,
The change isn't perceived when multiple people are sitting in the room and they hear the same thing it's definitely not perceived It's very apparent and the speaker is vibrating not from the woofers moving back and forth but from the vibrations coming through the floor back into the speaker again you really should watch Max Townshend explain all this stuff in the videos he's posted,Google Townshend podiums and you'll be able to o watch them.