The team from mythbusters assembled this large array of bass in an attempt to discover the "brown note".

Some of the frequencies they wanted to test were below the tuning point of the boxes which would mean unloading of the cones and overexcursion. The solution was to plug the ports, converting to sealed operation. The drop in output is why they used so many boxes. (not to mention that it made for good looking television!)

See the full writeup at the Meyer Sound site