edifier s550

I have one edifier s550.the manufacturer says the frequency response of the system is from 20-20000hz.but here is a graph of the response of the system by analyzer here the frequency is rolling off after 40hz.but many people are saying the lower end of graph may vary with different room condition.I played some tracks having low end frequencies(under 40hz to 20hz) and the subwoofer is vibrating but I can't feel any sound.my room is small and not so good.will it affect low frequencies.
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