SOUND The curved shape of part of the outer human car known as the external auditory meatus or ear canal helps focus sound as it is received Sound waves journey down the ear canal to a membrane called the ear drum Waves striking the eardrum cause it to vibrate From there sound waves travel to the middle ear where they are passed along a series of three small bones called ossicles and strike another membrane called the round window Finally sound moves into the inner ear to the shell like cochlea which houses the organ of Corti Covered in nerve endings that look like tiny hairs the organ of Corti sends electrical impulses to the brain where sound is identified There are many kinds of sounds and various ways to interpret those sounds But as this book explains the physics of sound are pretty straightforward as well as quite interesting 8
CHAPTER 1 MAKING SoUND E very kind of sound is produced by vibra tion The sound source may be a violin an automobile horn or a barking dog Whateveritis some part ofit is vibrating while it is producing sound The vibrations from the source disturb the air in such a way that sound waves are produced These waves travel out in all directions expanding in a balloonlike fash ion from the source of the sound If the waves happen to reach someone s ear they set up vibrations that are perceived as sound Sound then depends on three things There must be a vibrating source to set up sound waves a medium such as air to carry the waves and a receiver to detect them Sound waves cannot travel through a vacuum There is an age old question concern ing the definition of sound If a tree falls in a forest far from any sound detector such as a human ear or a microphone does the tree s crash make any noise The answer of course depends on how sound is defined If it is thought of as the waves that are carried by the air the answer is yes wherever there IO
MAKING SOUND sound waves Sound waves travel through the air from a source to a receiver Encyclopaedia Britannica Inc are sound waves there is sound However if sound is defined subjectively as a sensation in the car for example the answer must be no In that case sound does not exist unless there is a receiver present to detect it The two definitions are equally correct How SoUND Is PRODUCED AND CARRIED It is easy to detect the vibrations of many sources of sound A radio loudspeaker for example vibrates strongly especially when the volume is turned up If one lightly touches II
