Quick tutorial on the charts. Vert axis is frequency in Hz, Horiz axis is time in ms. Color is loudness or SPL in dB. (the colored bar to the right is actually a key showing the color coding used to indicate loudness in the chart - this can be confusing if you think it is part of the chart data).
A short loud pulse is delivered to the sub, and a microphone in front of the sub measures the response to that short pulse. The longer a sound hangs after the pulse is over, the muddier the bass will be. The chart for the E15HP shows a quick (and consistent with respect to frequency) die off of the sound level consistent with the input. The others show more overhang.
Here is a chart for you to refer to. This is the $500 SVS PB1000. It is tighter than the SUB-1200 in the higher frequencies, but the overhang on the low end is worse. For me, this bloat in the low end really compromises music sound quality, it overpowers the rest of the bass:
Ignore the next statements if they don't make sense! It is a detail that you don't need to understand to get the gist of it:
Note that the SUB-1200 and LV12R charts are only for the ports. That is why they don't extend into higher frequency. The E15HP and PB1000 charts are for the entire sub (no port exists). You can see charts for the drivers at the linked locations. The actual response would be the combination of the port and driver charts; however, that gets really confusing and the port charts adequately show the concept I am wanting to present.