Everyone instinctively holds a shell to their ear when they find one on the beach, trying to hear the sounds of the sea and oceans. But why can we hear sounds that resemble the ocean inside a shell? Trevor Cox, a professor of acoustical engineering at the University of Salford in the UK, explained, "It's not the sound of the sea, but since you are holding a shell to your ear, it makes sense for people to think it might be."
Andrew King, director of the Centre for Integrative Neuroscience at the University of Oxford and head of the Oxford Auditory Neuroscience Group, stated, "You hear ambient or background noise that is amplified because of the physical properties of the shell." King elaborated that "the solid and curved surfaces" inside the shells reflect sound waves, causing them to bounce within the shell. He added, in an attempt to explain the nature of the sound heard, "The shell acts as a resonator, amplifying certain sound frequencies, making them louder than they would be without placing the shell next to your ear."
According to King, the frequencies you hear depend on the size and shape of the shell. If the shell has an irregular shape, it is likely to resonate at multiple frequencies. Cox explained, "The shell is like a wind instrument; it contains a set of resonant frequencies where the air inside the shell vibrates more intensely. When the shell is pressed against your ear, those frequencies in the ambient sound are amplified, and because the sound changes, your brain pays attention to it."
Both Cox and King noted that you don’t actually need a shell to hear a sound that resembles ocean sounds; you can have a similar experience at home simply by using a cup or bowl. King mentioned, "The same effect occurs when placing other objects or even your cupped hand beside your ear; what you hear again depends on the size and shape of the object." However, King pointed out that "there needs to be background noise" for anything to be heard. He stated, "You wouldn't hear anything in a soundproof room." According to Cox, "If you went to a completely dead room at the University of Salford, which is entirely silent, you wouldn't hear anything because there is no ambient sound."
