What is the sound?
sound can be viewed as a wave motion in air or other elastic media. In this case, sound is a stimulus. Sound can also be viewed as an excitation of the hearing mechanism that results in the perception of sound. In this case, sound is a sensation. These two views of sound are familiar to those interested in audio and music.
Sound is a physical phenomenon as well as a sensual one. The relationships between the physical and sensual aspects of sound are complex in that many of the impressions sound makes on us are related to its physical parameters but not reducible to them. ‘The nature of sound’ considers the physical aspects of sound, which are far better understood than the emotional ones. It discusses pressure waves; how sound is carried; the velocity, refraction, frequency, and diffraction of sound; the power of sound, including loudness and the decibel measurement system; standing waves and resonances; charting sound; sound filters; and sound synthesis.
Speed of Sound:
The speed of sound in air is about 1,130 ft/sec (344 sec) at normal temperature and pressure. The speed of sound is dramatically slower than the speed of light (670,616,629 mi/hr). It takes sound about 5 seconds to travel 1 mile; you can gauge the distance of a thunderstorm by counting the time between the sight of the lightning strike and the sound of its thunder. The speed of sound in the audible range is not
appreciably affected by intensity of the sound, its frequency, or by changes in atmospheric pressure. Sound will propagate at a certain speed that depends on the medium, and other factors. The more dense the molecular structure, the easier it is for the molecules to
transfer sound energy; compared to air, sound travels faster in denser media such as liquids and solids. For example, sound travels at about 4,900 ft/sec in freshwater, and about 16,700 ft/sec in steel. Sound also travels faster in air as temperature increases (an increase of about 1.1 ft/sec for every degree Fahrenheit). Finally, humidity affects the velocity of sound in air; the more humid the air, the faster the speed. It should be noted that the speed (velocity) of sound is different from the particle velocity. The velocity of sound determines how fast sound energy moves across a medium. Particle velocity is determined by the loudness of the sound.
Wavelength and Frequency:
A sine wave is illustrated in Fig. 1-7. The wavelength λ is the distance a wave travels in the time it takes to complete one cycle. A wavelength can be measured between successive peaks or between any two corresponding points on the cycle. This also holds for periodic waves other than the sine wave. The frequency f specifies the number of cycles per second, measured in hertz (Hz). Frequency and wavelength are related as follows:
which can also be written as :
As noted, the speed of sound in air is about 1,130 ft/sec at normal conditions. For sound traveling in air: