Frequency Response?

Pbnaudio, We don't have exactly dry air here (Chicago) but I will settle for 1135ft/s which is speed of sound in dry air at 75degF - and this is my last offer.

Same example with new numbers: 1135/18/2=31.5Hz

62bakes: You can use just the high pass section of an active crossover, like a Marchand. Doing something similar with a NHT X2, which has a relatively simple choice of 3 fixed 12 dB/octave filters. Except for the Pass XVR-1, most active xovers use opamps which are not always totally transparent. 24 dB/octave filters are usually cascaded (series) but have their advantages. Then, there's digital xovers which require another ADC/DAC conversion but can offer incredible versatility.

A 5 string bass with a low B string creates, at least at the fundamental tone, a 31hz signal...using test tones I've found that my system (including a sub) easily reproduces that frequency, and a nice test is the bass note at the beginning of Donald Fagan's "Morph the Cat"...a solid B. I do use a phono preamp with a rumble filter (20hz), and before that (when I had a preamp with a phono stage) I found an older pair of Nakamichi line filters that worked really well to tame woofer rumble floppage. I think in live music there's a lot of stuff going on under 40hz, like kick drum overtones (undertones?) subway tunnels under the floor, or heavy footed waiters bringing my bar tab check.

In general, clipping due to low frequency noise being generated is fairly common with vinyl rigs. With digital, it is practically not really a concern. If speakers are producing poor or unneeded output of actual music signal at lower frequencies,then filtering is a good option to use power available more constructively.