Do you remember trying this as a kid—putting a sea shell you got as a souvenir next to your ear? It seems that no matter how far away you are from the ocean, when you hold a sea shell to your ear, you can hear the roar of the waves as they crash onto the shore. The best thing to use to create this sound is the spiral-shaped conch shell. Some people believe that the sounds heard from sea shells are the echoes produced by your blood flowing through the blood vessels in your ears. But this is not the case. If this is true, this sound would be intensified after exercise because blood flow speeds up after exercise. However, the sound level did not change even after exercise. Others believe that the whirring sound in the shell is caused by the movement of air in the shell - air flowing in and out of the shell creates a sound. You'll notice that when you hold the shell a little further from your ear, the sound is louder than when you hold the shell next to your head. However, this theory doesn't hold true when you're in a soundproof room. There is still air in a soundproof room, but when you hold a sea shell to your ear, there is no sound. The most likely explanation for this ocean-like sound is that it's the noise around you. These noises were transmitted to the sea shell placed above the ear, and produced a buzzing sound in the shell. Therefore, the size and shape of the shell will have a certain impact on the sound you hear. The sounds produced by different shells are also different, because different shells emphasize different audio frequencies. You don't even need a sea shell to hear it. Using an empty cup or even placing your hands over your ears can create the same "ocean" sound. Go experiment with this and vary the distance between the cup and your ear. As the angle and distance between the cup and your ear changes, the pitch of the sound changes. The sound outside the shell also changes the intensity of the sound you hear from inside the shell. You can think of the shell as a singing chamber. The sound from the outside is transmitted into the shell, and is constantly collided and reflected, thus forming a sound that can be heard. So, the louder the surrounding environment, the louder the ocean-like sound you hear.