Chapter 13

This chapter is the story of sounds it is the story of how sounds are made, how sounds differ, how they travel, how they are detected, and how they may be controlled.

Our language reflects our keen awareness of sound. In the country we mark the hum of mosquitoes, the rustle of leaves, the lowing of a cow, the flutter of wings, the roar of a waterfall. In the city we note the blare of automobile horns, the rumbling of trains, the blast of factory whistles, the patter of children’s feet, the cries of street vendors. Each season, each mood of nature is announced by its own special sound. Humans also make sound combinations evoked from musical instruments, such as violin strings, organ pipes, and drums.

Whenever a sound is produced, there must be something quivering, trembling, and shaking back and forth. In other words, vibration leads to sound. How is sound transmitted? When something vibrates, it imparts its trembling motion to the air particles around it. These molecules, in turn, pass the vibratory motion to the air molecules adjacent to them. In this way the vibration travels out ward in all directions form its source. How do we hear sound? A small part of the wave strikes a little membrane in your ear and cause the trembling of the eardrum which is then converted into electrical energy and triggers the nerve impulses. These impulses travel along the auditory nerve to the brain. We then perceive sounds. How do we distinguish among many sounds? We identify sounds by three characters of sounds which are loudness, pitch, and quality. Loudness of sounds depends on how powerful the source of sound is and the distance of listeners from the sources. It is measured by the decibels. The larger the decibels of sound are, the greater the amplitude of the sound wave is. Loud sounds are universally disliked because they cause hearing impairment of people who are not immunized from it. The pitch of the musical notes is another way of saying the frequency of the vibration in the instruments. Three factors response for the difference in the pitch of various strings in an instrument. They are length, weight, and tightness. Low notes are produced by long, heavy, and loose strings. High notes are made by the opposite kinds of strings. Two sounds of the same loudness and pitch can be different. That is due to the “shape” of the sounds are different. The quality of sounds is an obscure terminology.