An infrasonic subwoofer would be an exercise in futility if there's no infrasonic content in my music and movies. Therefore, I decided to find out what's in there.
These are tracks I would actually listen to, not "demo" tracks, or organ CDs and the like.
I am ranking these tracks in descending order, from one hertz to about forty.
Here's a spectrum analysis of "Ask Yourself" by Plastikman. We see the beat at 44hz, along with a second harmonic at 88hz. When listening to the track, you can hear an ominous ambient rumble in the track. Over my fifteens, it's audible, but buried beneath the beat. In the spectrum analysis, we see that it digs all the way down to THREE HERTZ, peaking just 8dB below the bassline!
According to Geddes, three subs improve the bass response in-room. If three is good, I figured eight is great. After installing eight subs, this was the track that really caught my attention. It sounds *completely* different with a serious set of subs. In the frequency analysis, we can see why. On a typical system, we'll hear the bassline at 46hz. But look what's going on down deep - the fundamental is actually at 23hz! That explains the added "weight" over the eight subs.
Here's an analysis of "The Humpty Dance" by Digital Underground. There's serious content all the way down to 30hz. You can see that this track would be forgiving on a cheap sub, because the bass line is "doubled". So this would mask 2nd harmonic distortion. Compare that bass line to the Plastikman bassline, where the fundamental is not only low, it's much louder than the harmonic. (IE, the Plastikman track will show off a clean sub.)
Here's a couple samples from the Matrix. The first is a thunderclap, the second is from the shootout scene where the concrete walls are crumbling. Not a whole lot here below 30hz. It looks like it's been high-passed. Looking at this graph, you can see how it would also be forgiving of a cheap sub, due to the spectrum content.
To sum it up, if you're speakers only go to 30hz, you're probably not missing a whole lot. Almost all the "bass" energy is in the octave from forty to eighty hertz. But there *are* a handful of tracks with synthetic bass lines that can only be heard properly if your speakers are flat to 20, or even 18hz. And yes, there's even bass down to 3hz.
Analysis was done with Audacity, using the instructions from Sourceforge.