Seashell resonance

This effect is similarly observed in any resonant cavity, such as an empty cup or a hand clasped to the ear.

The resonant sounds are created from ambient noise in the surrounding environment by the processes of reverberation 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.

Resonators attenuate 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.

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