adding on to Dan_ed's post, from what i could figure out the fundamental at 40 Hz has a subharmonic at 20 Hz as well as overtones at 80 /160. it is a combination of all of these which give the flesh/timbre to the tone.
Any graphic equalizer using a digital out (eg i used a DEQ2496) shows a surprising amount of music in the 20-25hz region in many peices. the most surprising revelation has been "GrandMas hands" by Livingston Taylor. supposed to be an Acapella but has a consistent 20-25 hz bass content which is not heard in anything but a fullranger OR with subs and once you hear it that way can never ever listen to it without that bass fabric!
Any graphic equalizer using a digital out (eg i used a DEQ2496) shows a surprising amount of music in the 20-25hz region in many peices. the most surprising revelation has been "GrandMas hands" by Livingston Taylor. supposed to be an Acapella but has a consistent 20-25 hz bass content which is not heard in anything but a fullranger OR with subs and once you hear it that way can never ever listen to it without that bass fabric!