VLF - Very Low Frequency (60 Hz, 40 Hz, 20 Hz, 10, Hz 5 Hz test tones) - PSA

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Notice that 60 Hz sounds like a ground loop, also called a 60 cycle hum. That’s because ground loop hum is a 60 Hz sine wave. However, some 60 cycle hums contain harmonics of 60 Hz, usually at low amplitudes. Harmonics of 60 Hz include, 120 Hz, 180 Hz, 240 Hz, 300 Hz, 360 Hz, etc. In the UK, the electrical system is based on 50 Hz. The harmonics of a 50 Hz hum would be calculated as such; 50x1, 50x2, 50x3, 50x4, 50x5, and so on.

PSA - Can you hear VLF (very low frequencies)? Can you feel them? Do they have the potential to cause harm to humans? Between 5 and 9 Hz the hypothetical Brown Note is rumored to cause humans to lose control of their body due to resonance. According to Wiki, "The brown note is a hypothetical infrasonic frequency that would cause humans to lose control of their body due to resonance. Attempts to demonstrate the existence of a "brown note" using sound waves transmitted through the air have failed." https://en.wikipedia.org/wiki/Brown_note

There are two important acoustical and electrical properties to consider. Many speakers are too small to reproduce those wave lengths. They would only be able to manage harmonics of the fundamental, but that's not the same thing, although in a psychoacoustic way, the mind can perceive the fundamental, (notes at the lower end of the piano, not VLF). Also, VLFs need enormous amounts of power. A system’s ability to produce sound is often measured in sustained reproduction and burst reproduction. Reproducing VLFs in bursts is difficult, sustaining reproduction is a great challenge. Remember that energy produces heat. And heat is the enemy of amplifier efficiency. Attempting to sustain 5 Hz at a high volume would require tremendous energy which would produce an enormous amount of heat. Specially designed radiators would be needed to deal with this heat. This causes the system’s size to grow exponentially. The problem starts to become clear. Parts of amps would literally begin to melt if pushed hard enough to reproduce a 5 Hz tone at a volume loud enough to for a human too feel it.

I'll leave it at that and let someone else take it further.