Seashell resonance
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Seashell resonance refers to a popular folk myth that the sound of the ocean may be heard through
seashell A seashell or sea shell, also known simply as a shell, is a hard, protective outer layer usually created by an animal or organism that lives in the sea. Most seashells are made by Mollusca, mollusks, such as snails, clams, and oysters ...
s, 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 (mollusc), spire and a noticeable siphonal canal (in other words, the shell comes to a noticeable point on both ...
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 resona ...
, 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#Characteristics, koala (which has two thumb#O ...
clasped to the
ear In vertebrates, an ear is the organ that enables hearing and (in mammals) body balance using the vestibular system. In humans, the ear is described as having three parts: the outer ear, the middle ear and the inner ear. The outer ear co ...
. The resonant sounds are created from ambient noise in the surrounding environment by the processes of
reverberation In acoustics, reverberation (commonly shortened to reverb) is a persistence of sound after it is produced. It is often created when a sound is reflection (physics), reflected on surfaces, causing multiple reflections that build up and then de ...
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. 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 variable at ...
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 voice, chewing, footsteps, or any other sounds originating in th ...
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