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What does 21 Hz sound like?
21 Hz is a sub-bass frequency. It is a very deep sub-bass tone that you feel in your chest as much as hear. Small speakers struggle to reproduce it; good headphones or a subwoofer will.
A 21 Hz sound wave completes 21 cycles every second, so one cycle lasts 47.6 ms. In air at 20 °C, where sound travels at about 343 m/s, each wave is 16.33 m (53.59 ft) long; in water it stretches to 70.52 m because sound moves about 4.3 times faster there.
Musically, 21 Hz is 33 cents above E0 (20.6 Hz) in standard A440 tuning. Doubling it to 42 Hz raises the pitch by one octave; halving it to 10.5 Hz lowers it by one.
Wavelength of 21 Hz in different materials
| Medium | Speed of sound | Wavelength |
|---|---|---|
| Air (20 °C) | 343 m/s | 16.33 m |
| Fresh water | 1,481 m/s | 70.52 m |
| Seawater | 1,500 m/s | 71.43 m |
| Helium | 1,007 m/s | 47.95 m |
| Steel | 5,960 m/s | 283.81 m |
| Glass | 5,640 m/s | 268.57 m |
Harmonics and octaves
Real instruments playing 21 Hz also produce harmonics at whole-number multiples of the fundamental. Their relative strength gives each instrument its timbre.
Which animals can hear 21 Hz?
Cannot hear it
Dogs, Cats, Horses, Cows, Sheep, Pigs, Goats, Rabbits, Rats, Mice, Gerbils, Guinea pigs, Hedgehogs, Raccoons, Opossums, Chinchillas, Bats, Beluga whales, Bottlenose dolphins, Chickens, Canaries, Budgerigars (parakeets), Cockatiels, Owls, Bullfrogs, Tree frogs, Catfish, Tuna, Greater wax moths
Frequently asked questions
What does 21 Hz sound like?
It is a very deep sub-bass tone that you feel in your chest as much as hear. Small speakers struggle to reproduce it; good headphones or a subwoofer will.
Can humans hear 21 Hz?
Yes. 21 Hz is inside the typical human hearing range of 20 Hz to 20 kHz.
What musical note is 21 Hz?
21 Hz is 33 cents above E0, which is 20.6 Hz in standard A440 tuning.
What is the wavelength of 21 Hz?
About 16.33 m in air at 20 °C and 70.52 m in water.
Can dogs hear 21 Hz?
No – dogs hear roughly 67 Hz to 45,000 Hz.