Some people believe that the cause of the noise is due to the blood flowing through our blood vessels, others due to the movement of air currents. But as experts say, both options are wrong.
In childhood, everyone tried to bring a shell to their ear, which they bought at sea as a souvenir. It seems that no matter how far you are from the sea, you can still put a shell to your ear and hear the roar of the waves rolling on the shore. The best shells to reproduce this sound are large spiral shells, according to Science How Stuff Works.
Some people assume that the sound we hear from a seashell is an echo of blood running through the blood vessels of the ear. However, it doesn't work that way. If this were true, then, for example, after a workout, the sound would increase, because after physical activity the blood runs faster.
Others say that the whistling sound is created due to the movement of air currents through the sink. If the shell is held a short distance from the ear, then the noise seems much stronger than if the shell is brought directly to the ear. However, this theory does not work in a soundproof room. There is still air in a soundproof room, but when you hold a shell to your ear, there will be no sound.
But as scientists note, the most likely explanation for the sound produced inside the shell is ambient noise. The shell you hold just above your ear picks up this noise that resonates inside the shell. So the size and shape of the shell has some effect on the sound you hear.
Different shells sound different because they emit different frequencies. You don't even need a seashell to hear the noise. You can reproduce the same “marine” sound using an empty cup or even by pressing your palm to your ear. Try and vary the distance at which you bring the cup to your ear. The sound level will vary depending on the angle and distance of the bowl from your ear.
Noise from outside the sink can also change the intensity of the sound you hear inside. When sound from outside hits the shell, it is reflected, creating an audible noise. Thus, the louder the environment you are in, the louder the sound of the “sea” will be.