When an object makes a noise, it sends vibrations, sound waves, speeding through the air. These vibrations are then funneled into your ear canal by your outer ear. As the vibrations move into your middle ear, they hit your eardrum and cause it to vibrate as well. This sets off a chain reaction of vibrations. The cochlea, a tube in the inner ear, contains thousands of nerve endings called cilia. When the fluid in the cochlea vibrates, the cilia move. The cilia change the vibrations into messages that are sent to the brain through the auditory nerve. The auditory nerve carries messages from 25,000 receptors in your ear to your brain. Your brain then makes sense of the messages and tells you what sounds you are hearing.





Underwater Hearing


Sound underwater travels five times faster than in air. You would think that this means it is easier to hear underwater but that is not so. Volume is not affected by sound but the sound waves and their environment do. There are two methods of perceiving sound waves, air conductivity and bone conductivity. Bone conductivity receives sound through vibrations in the bones of the skull. Air conductivity is useless underwater because the ear is filled with water, making the structures unable to receive sound waves. Therefore bone conductivity is what is used underwater. The distance within which sound can be heard depends on tonality rather than on the volume of sound. Sounds of greater tonality can be heard at greater distances than those of lower tonality. Sounds that are made underwater are usually inaudible above the surface of the water and vice versa.







Measurement of Sound


Scientists measure loudness in decibels. Below is a table of various noises and their decibel level.



In sound measurement, voltage is also used.




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