Sarang, welcome. The studies I've read(most notably by THX)indicate that 80Hz is the lowest frequency which is localizable. It varies with individuals and rooms and in some cases even 150Hz was non-directional. I use an 80Hz crossover for all speakers, regardless of a lower bass extension capability.
Arguments of some that separate bass reproduction should be carried down to very low frequencies, at least for two channels, and even better, for all, haven't been proven by experimental evidence. For example, Dr. Toole, briefly discussing this in "Sound Reproduction" at pp. 238-239, titles the section "Stereo Bass: Little Ado about Even Less"(with apologies to Shakespeare).
