I'd be curious to know how those measurements were taken, as room response can generate significant dips and peaks. Seeing as Outlaw rates the sub to be +/-2dB across its range under ideal conditions and without any details about the origin of the graph you saw, I would suspect that the graph included some uncorrected room effects.

According to the Outlaw site, the LFM-2 starts to roll off at 28Hz while the (now discontinued) LFM-1 went to 25Hz. I suspect that the "25Hz" figure for the LFM-2 is a cut/paste typo in the manual. The LFM-1 Plus will reach 25Hz in high output mode or 18Hz in max extension mode. A +/-2dB rating is actually more conservative than most manufacturers, as a +/-3dB rating is more common (lets to list a somewhat lower bottom figure).

As for being flat down to 40Hz, I've been told that the SMS-1 calibration sample in the Outlaw Guide to the SMS-1 was made using an LFM-1. The graph on page 24 shows a response corrected to (at least mostly) eliminate room response issues and looks pretty darn flat all the way down to 25Hz (15Hz below the point where you are seeking a level response).

In addition to the LFM-2 and LFM-1 Plus currently available from Outlaw, there are two subs expected to arrive in the next month or two. The LFM-1 Compact will use a 10" driver and will get down to 25Hz (click here for a press release), and the LFM-1 EX will use a 12" driver in a cabinet somewhat larger than the LFM-1/LFM-1 Plus used and will reach 22Hz with both ports open or 16Hz with one port plugged (see this press release ).