Why Can You Hear the Ocean in a Seashell?

The Sound Heard In A Seashell

• The surrounding background noises, or ambient sound waves are vibrating air that gets inside the seashell's cavity and resonates when held to the ear. The shape of the seashell makes it an excellent noise amplifier. How a seashell creates sound is through a Helmholtz resonance, where the air inside a container with an opening can vibrate. Seashells are not the only vessels that can capture surrounding environmental sounds. Any type of solid, hollow, partly enclosed vessel such as a mug, cup or glass that has a gap to allow sounds to enter, can produce ocean-like sounds.

Seashells As A Helmholtz Resonator

• A Helmholtz resonator, based on the research of Herman L. F. Helmholtz, is a hollow container such as a bottle with an open hole or neck. Helmholtz's research mathematically describes how the air volume in the open hole of the bottle vibrates -- such as when an individual blows across the hole -- due to the springiness of the air inside that causes it to make a noise. A seashell acts as a Helmholtz resonator because the vibrating air of the ambient sound waves enter the cavity of the seashell and causes the existing air inside the seashell to vibrate. The sounds bounces around the curved seashell wall and makes a resonating sound, that when held to or near the ear, that is reminiscent of the roaring waves of the ocean. The constant bouncing of the air inside the seashell also amplifies collected ambient noises and alters the frequency, or pitch of the sound.

Seashells' Sound Frequencies

• Whether the resonating sounds heard in a seashell, or similar vessel are high-pitched or low-pitched depends on its size. Larger seashells and vessels produces lower, bass sounds because it takes a moment for the sound to bounce around the inner walls. While smaller vessels produces a higher sound. No matter the size of the seashell or vessel, it produces an ocean-like sound.

Contrary Theory

• One theory claims that when a seashell is held to the ear, the sound heard is blood rushing through blood vessels in the ear. If this were true, blood coursing through blood vessels would be heard after exercising because blood rushes faster after exercise. However, the sound of blood stays the same.