[mcbits]

20Hz and 20KHz are just general guidelines for where sensitivity rapidly falls to zero in people with normal hearing. A lot of (primarily young) people can hear frequencies outside that range. I can still hear a sine wave down to about 14Hz, and I'm not sure if the limit is from my ears or the audio interface that's only rated down to 20Hz.

I can imagine "feeling" 1Hz from a big subwoofer, but it's hard to imagine what actually hearing 1Hz would be like. I wouldn't rule it out, though.

[archi42]

You're sure you're not hearing some harmonic? IIRC THD at lower frequency increases drastically. Or wind noise of the subs (they're moving lots of air)?

You can check with a measurement mic what's audible (& make sure to take measurements at multiple points in space due to the low wave length).

To decrease the lower frequency of the audio interface, you probably have to modify the output DC decoupling capacitors (those act as a high pass; bigger C = lower f).