Using the same woofers, the response was measured after installation into this dual band pass horn. The results of that are indicated by the red line in the chart. 

The yellow area represents a serious gain in efficiency between the two enclosures. The dual band pass enclosure is also smaller in size by 1 cubic foot. 

This illustration is very conservative. By watching the impedance vs. frequency response of a ported box it is easy to understand why a properly sized and ported enclosure will offer increased power handling at the frequency of that port. But, the way this horn loaded design works is similar to having several ports working at several frequencies. We call it "a rubber throat" because the "port" if you will, or better spoken- "the mouth" of the horn changes in size and length depending on the frequencies it reproduces. I know this is hard to follow if you're not up on horn loaded enclosures so just remember the following: 

A port resonates at a given frequency determined by the length and diameter of the port, while a horn resonates at a HI frequency and a LO frequency and EVERY frequency between the two. For this reason the woofer is dampened at every frequency between LO and HI. That's why it has such phenomenal accuracy, gain, and bandwidth.