What is very low frequency used for?

The VLF band is used for a few radio navigation services, government time radio stations (broadcasting time signals to set radio clocks) and for secure military communication . Since VLF waves can penetrate at least 40 meters (131 ft) into saltwater, they are used for military communication with submarines.

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What Hz is low frequency?

Sound at 20-200 Hz is called low-frequency sound, while for sound below 20 Hz the term infrasound is used. The hearing becomes gradually less sensitive for decreasing frequency, but despite the general understanding that infrasound is inaudible, humans can perceive infrasound, if the level is sufficiently high.

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