It is the FOH that counts, though there's not many PAs in small to medium venues that will accurately reproduce 30Hz at any volume. You'll get hints of it, but as Dan says you'll get far more in the way of overtones which just point at it.
The problem is that PA systems are designed to be efficient so they go very loud, unlike some hifi systems which can be just the opposite. I've got 2 pairs of Hifi speakers that will produce 30Hz at volume - Leema Xaviers which have an F3 point of 28Hz and Ditton 66/series 2s which have an F6 of 18Hz. However, I need to use a Bryston power amp which produces 968w RMS/channel to do that. And both speakers are around 86dB/w efficient, so they soak up the power!
However, if your 4x10 cab is a Mesa Subway 4x10 has an efficiency of 100.4dB/w, which of course means they have far less extension that my hifi speaks (but will go a lot louder!) - the actual F3 figure (i.e. where output is 3dB below the mid frequency level) is 59.4 Hz, with an F10 figure(which equates to being half as loud as F3) of 41.3Hz. So if you're lucky, the output at 30Hz is likely to be 1/4 as loud as the F3! So you're actually not going to be reproducing much at 30Hz either FOH or from speaker monitoring.
Your IEMs may reproduce it, but that doesn't help the audience, and the electronics are largely irrelevant as most have at least a range of 20-20000Hz.
If you want to get nearer to a magical 30Hz at volume, the Mesa Subway 2x15 will do F10 @ 37Hz... But a Trace 1818, if you've got the back for it, will give an F6 of 28Hz...