I'm confused. An organ goes as low as 8Hz. A tuba goes to 16Hz. A standard string bass as low as 41Hz. These are all non-electronic and go into actual sub-bass frequency range (lower than 60Hz).
Here's a good reference: http://www.contrabass.com/pages/frequency.html
I thought we were talking about Hans Zimmer's work on the Dark Knight Rises. I wasn't referring to any sub-bass in that soundtrack but the cello/double bass ensemble which is in my opinion a great piece of music to judge your headphone's capabilities.