If one plugs two of the SVS’s three ports, one can tune the low end of the sub down to “16Hz.” However, this is not “free” low-end response. See the online manual for the SVS PB12-ISD/2 and the output vs. frequency chart on page 10. If one plugs two ports, the frequency response starts gently falling off above 60Hz, is –3db lower than without the plugs at about 40Hz, and at 16 – 25Hz is –4db to –6db down. There is a similar but slightly more mild effect if one plugs one of the three ports to tune the SVS down to “20Hz.” While this roll-off seems to have a gentle slope and would not affect the output in an irregular manner, the user makes a choice: rather level output down to near 25Hz or a lowered/falling output down to 20Hz or 16Hz.

As to two LFM-1’s, as discussed elsewhere, there is a mildly improved low end when two identical subs are ‘coupled’ in a room environment, and there are other advantages to either a multiple mono or stereo subwoofer setup. I wouldn’t toss out the idea of two LFM-1’s based on the idea that a single SVS can be tuned lower than a single untuned LFM-1.