That 22hz frequency response is stated as in room and the graphs you are looking at are groundplane measurements. Two different animals and should be interpreted as such. There should be a +- stated by the manufacturer in that spec though. Those graphs do not take into consideration room gain and interactions which is the whole purpose of those graphs. They are actually pretty good measurements at that price point and typical of a lot of subwoofers (even more expensive ones). We just don't see raw graphs on most subs especially budget ones. Keep perspective that isn't a high end sub.
P.S In room specifications that manufacturers use are ways for manufacturers to fudge specs to make them more pretty then they are.
