The rushing sound that one hears is in fact the noise of the surrounding environment, resonating within the cavity of the shell. The same effect can be produced with any resonant cavity, such as an empty cup or even by simply cupping one's hand over one's ear. The similarity of the noise produced by the resonator to that of the oceans is due to the resemblance between ocean movements and airflow.
The resonator is simply attenuating some frequencies of the ambient noise in the environment, including air flowing within the resonator and sound originating within the human body itself, more than others.
The human ear picks up sounds made by the human body as well, including the sounds of blood flowing and muscles acting. These sounds are normally discarded by the brain; however, they become more obvious when louder external sounds are filtered out. This occlusion effect occurs with seashells, cups, or hands held over one's ears, and also with circum-aural headphones, whose cups form a seal around the ear, raising the acoustic impedance to external sounds.
- Gerard Cheshire (2006). Sound and Vibration. Black Rabbit Books. p. 25. ISBN 1-58340-997-1.
- Joseph P. Olive, Alice Greenwood, and John Coleman (1993). Acoustics of American English Speech: A Dynamic Approach. Springer. p. 64. ISBN 0-387-97984-0.
- Dorita S. Berger (2002). Music Therapy, Sensory Integration and the Autistic Child. Jessica Kingsley Publishers. pp. 86–87. ISBN 1-84310-700-7.
- John Watkinson (1998). The Art of Sound Reproduction. Focal Press. ISBN 0-240-51512-9.