sorry if i was being obtuse
by ’l-f’ -- i simply mean low frequency
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to add to the discussion, i would remind the op and others here interested that
a) speaker placement for effective/optimal boundary reinforcement of low frequencies,
b) treating a room to address unwanted resonances/nodes and reflections
c) correctly integrating subwoofer(s)
may be somewhat inter-related but are different things, each with different benefits, solving for different deficiencies