Seashell resonance refers to a popular folk myth that the sound of the ocean may be heard through seashells, particularly

conch Conch () is a common name of a number of different medium-to-large-sized sea snails. Conch shells typically have a high spire and a noticeable siphonal canal (in other words, the shell comes to a noticeable point at both ends). In North Am ...

shells. This effect is similarly observed in any

resonant cavity A resonator is a device or system that exhibits resonance or resonant behavior. That is, it naturally oscillates with greater amplitude at some frequencies, called resonant frequencies, than at other frequencies. The oscillations in a resonato ...

, such as an empty cup or a

hand A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the koala (which has two opposable thumbs on each "h ...

clasped to the ear. The resonant sounds are created from

ambient noise Background noise or ambient noise is any sound other than the sound being monitored (primary sound). Background noise is a form of noise pollution or interference. Background noise is an important concept in setting noise levels. Background n ...

in the surrounding environment by the processes of

reverberation Reverberation (also known as reverb), in acoustics, is a persistence of sound, after a sound is produced. Reverberation is created when a sound or signal is reflected causing numerous reflections to build up and then decay as the sound is abso ...

and (acoustic) amplification within the cavity of the shell. The ocean-like quality of seashell resonance is due in part to the similarity between airflow and ocean movement sounds. The association of seashells with the ocean likely plays a further role. ''Blood flow in the ear resonates in the shell causing an sound similar to the sound of waves.'' Resonators

attenuate In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at vari ...

or emphasize some ambient noise frequencies in the environment, including airflow within the resonator and sound originating from the body, such as bloodflow and muscle movement. These sounds are normally discarded by the

auditory cortex The auditory cortex is the part of the temporal lobe that processes auditory information in humans and many other vertebrates. It is a part of the auditory system, performing basic and higher functions in hearing, such as possible relations to ...

; however, they become more obvious when louder external sounds are filtered out. This

occlusion effect The occlusion effect occurs when an object fills the outer portion of a person's ear canal, causing that person to perceive echo-like "hollow" or "booming" sounds generated from their own voice. The bone-conducted sound travels to the cochlea thro ...

occurs with seashells and other resonators such as circumaural headphones, raising the acoustic impedance to external sounds.

References

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External links

How Stuff Works
Mollusc shells Acoustics