Where do your bass frequencies disappear? Now think back to how many times you twiddled with the sub-60Hz range trying to get the bottom right. No surprise that it was difficult; you couldn't hear it! (Try this on your favorite headphones, too.)
 

 
How much musical information exists down there in the first place is another topic for discussion. Yes, the fundamental frequency of the low E string on a bass is 41.2 Hz, but there's a good chance you've never heard that, either.
 
(BTW, on my own system, which includes a sub, things drop off pretty rapidly below 50 Hz and are completely gone about 42 Hz.)

bitflipper
How much musical information exists down there in the first place is another topic for discussion. Yes, the fundamental frequency of the low E string on a bass is 41.2 Hz

Just what exactly are you implying about us bass players here? 

drewfx1

bitflipper
How much musical information exists down there in the first place is another topic for discussion. Yes, the fundamental frequency of the low E string on a bass is 41.2 Hz

Just what exactly are you implying about us bass players here? 

We can't be herd.

Listening on an old pair of Beats (by Dre) at work, and it completely dropped off at 19 Hz (the tone started to vibrate around 26-27 Hz).  

Bapu only needs to get down to Am anyway...

drewfx1

bitflipper
How much musical information exists down there in the first place is another topic for discussion. Yes, the fundamental frequency of the low E string on a bass is 41.2 Hz

Just what exactly are you implying about us bass players here? 

That we can't play after we hit 42 years old? Nahhhh ... can't be right!

Record low "E" on a bass, then apply a steep LPF at 60 Hz so that all of its harmonics are suppressed. If you have any bass left at all, you'll probably have to turn it up by 20-30 dB to hear it. Now do the opposite: apply a steep HPF at 80 Hz so only the fundamental is removed. Surprise - the bass sounds pretty good, even with its lowest frequencies gone.

The test in the OP is a little deceiving, because it's a constant amplitude all the way down. That doesn't happen in music productions because the characteristics of human hearing require you to favor the low end.
 
Another potential problem is that your speakers may start to distort, and when that happens you think you're hearing 40 Hz when in fact it's the third harmonic you're hearing. Play back the test at a low-enough volume to avoid harmonic distortion.
 

By slowly increasing the volume as the freq dropped, I was able to clearly discern the signal down to ~40hz in both headphones and my sub-equipped monitoring system.  At 41-40, the rolloff was pretty steep.
 
If at some point what I was hearing shifted from fundamental to harmonic, the shift was cross-faded extremely well

What I "thought" I heard: tone down to the high 40s, then more of a slight rumble from mid 40s down to about 37 Hz, then nada.
 
Edit: And I thought I heard a dip in volume around the crossover frequency of my monitors. Gotta check that!