One implication of the Fletcher-Munson curves is that the ear is quite sensitive to changes in SPL at low frequencies (recall that the curves bunch up in the bass region). Thus a 5 dB change at 40 Hz or so is subjectively comparable to a 10 dB change at 1 kHz. So a small change in SPL makes a disproportionately large change in perceived loudness in the bass region.
The ear’s sensitivity to small changes in SPL in the bass region implies that it’s pretty good at detecting the unnaturally lumpy bass that most rooms impose on speakers. Which in turn implies that we can expect significant subjective improvement from adopting an approach that smoothes out the in-room bass. While I’m an advocate of distributed multisub systems, ime improvements can show up simply from locating the bass sources in a speaker (the woofers and ports) at different distances from the room boundaries as much as is feasible.
As for fairly compact speakers that can do 20 Hz, I once loaned a pair of high-efficiency stand-mount speakers (about 1 cubic foot internal volume) to an equalizer manufacturer for an audio show. He planned to use a subwoofer system as well (not one of mine). The subwoofer crapped out the first day of the show, which would have been a disaster, but this guy was pretty resourceful. You see, my speaker had a large woofer (12") with good excursion (9 mm) and high thermal power handling (900 watts music program). So he used a powerful amp and dialed in a lot of EQ and as I recall he got ballpark 20 Hz bass after all, according to his measurements. Of course this was in a boomy hotel room, which in this case was helpful. Now I didn't sell the speaker packaged with his equalizer so my example doesn't really count, but it does illustrate one way to get 20 Hz at useful SPL from a fairly small box: Aggressive equalization of a woofer that can handle it.
Duke
dealer/manufacturer
