I know these are overdue.
First, two port configuration with rumble filter set to ON. This is the position that we "ask" the customers to set for 2ports, tuned to 18hz. It is not an option. Here is the result with low pass filter (LPF) switch at AVR/12:
The phase shift is a bit high compared to a sealed sub. That is the trade-off between sealed and vented. For the least phase shift mode, we have 1 port tuning:
The above is the 1 port tuned to 12hz, same as the condition as 2port. But here we ask the customer to set the rumble filter to "OFF". The extension is not quite 12hz. The purpose of this configuration is to reduce as much phase shift as possible. As a result, I let it roll off more naturally. Notice the phase shift at 20hz is 180 degrees. Just 90 degrees higher than our sealed subs. Note that our sealed sub at 14hz/high damping has one of the lowest phase shift and group delay among all subs tested by Ilkka.
Rumble filter off position has a build-in FR contouring circuit such that the two FR (18hz and 12hz tune) will line up exactly, so customers do not need to run Audyssey or other room EQ program again when switching between the two as shown next.
As long as the customer keep the volume and extension filter setting the same, just 1) plug (or uplug) 1 of the port, 2) flip the rumble filter to the correct position, and the two FR will overlay exactly like above.
For those who believe extension up to 200hz is necessary to get good HT sound, we have LFE mode in selected models and this is FR of 2port in that mode.
We would recommend against using this because the port resonance of vented sub will be in the frequency range between 100hz and 200hz as seen in the above plot. We want to attenuate that as much as possible, not as little as possible. In addition, this type of port resonance is not unique to our vented subs, it is in fact in very vented sub because of the length of port(s) required by such low tuned frequency.