It's also important to realize that especially with infrasound, you're always exposed to it along with most regular sounds.
The modulation applied to sound to turn it into speech (i.e. amplitude and frequency shifts on order ~0.5-2 Hz) shows up in the frequency spectrum at those sorts of frequencies.
If you say "hey hey hey hey hey", that's a 1 Hz-or-whatever sound wave you're producing with a higher frequency carrier wave.
It's also important to realize that especially with infrasound, you're always exposed to it along with most regular sounds.
The modulation applied to sound to turn it into speech (i.e. amplitude and frequency shifts on order ~0.5-2 Hz) shows up in the frequency spectrum at those sorts of frequencies.
If you say "hey hey hey hey hey", that's a 1 Hz-or-whatever sound wave you're producing with a higher frequency carrier wave.