"Don't believe everything you read on the forum, the only way to know how loud a sub is you have to meter it. How far a sub moves is mostly determined by the frequency played and the box tuning. If you are playing notes at or near box tuning the sub will have very low excursion. High excursion by a sub usually indicates notes/frequency are being played below the box tuning. While this may look impressive it does not mean the sub is louder and the sub is "unloading" which is very bad for the sub.
If you want to find out how loud the sub is have it metered.
You do need to build another box."
-by DJ tha man