1-22
waveforms. Tone A is a simple wave of a specific frequency that can be produced by a tuning fork, piano,
organ, or other musical instrument. Tone B is also a simple wave but at a different frequency. When the
two tones are sounded together, the complex waveform in tone C is produced. Note that tone C has the
same frequency as tone A with an increase in amplitude. The human ear could easily distinguish between
tone A and tone C because of the quality. Therefore, we can say that quality distinguishes tones of like
pitch and loudness when sounded on different types of musical instruments. It also distinguishes the
voices of different persons.
Q20. What are the two general groups of sound?
Q21. What are the three basic characteristics of sound?
Q22. What is the normal audible range of the human ear?
Q23. What is intensity as it pertains to sound?
Q24. What characteristic of sound enables a person to distinguish one musical instrument from
another, if they are all playing the same note?
ELASTICITY AND DENSITY AND VELOCITY OF TRANSMISSION
Sound waves travel through any medium to a velocity that is controlled by the medium. Varying the
frequency and intensity of the sound waves will not affect the speed of propagation. The ELASTICITY
and DENSITY of a medium are the two basic physical properties that govern the velocity of sound
through the medium.
Elasticity is the ability of a strained body to recover its shape after deformation, as from a vibration
or compression. The measure of elasticity of a body is the force it exerts to return to its original shape.
The density of a medium or substance is the mass per unit volume of the medium or substance.
Raising the temperature of the medium (which decreases its density) has the effect of increasing the
velocity of sound through the medium.
The velocity of sound in an elastic medium is expressed by the formula:
Even though solids such as steel and glass are far more dense than air, their elasticity’s are so much
greater that the velocities of sound in them are 15 times greater than the velocity of sound in air. Using
elasticity as a rough indication of the speed of sound in a given medium, we can state as a general rule
that sound travels faster in harder materials (such as steel), slower in liquids, and slowest in gases.
Density has the opposite effect on the velocity of sound, that is, with other factors constant, a denser
material (such as lead) passes sound slower.
At a given temperature and atmospheric pressure, all sound waves travel in air at the same speed.
Thus the velocity that sound will travel through air at 32º F (0º C) is 1,087 feet per second. But for
practical purposes, the speed of sound in air may be considered as 1,100 feet per second. Table 1-1 gives
a comparison of the velocity of sound in various mediums.
