The material through which sound waves travel is called the medium. The density of the medium
determines the ease, distance, and speed of sound transmission. The higher the density of the medium, the
slower sound travels through it.
The detector acts as the receiver of the sound wave. Because it does not surround the source of the
sound wave, the detector absorbs only part of the energy from the wave and sometimes requires an
amplifier to boost the weak signal.
As an illustration of what happens if one of these three elements is not present, lets refer to our
experiment in which a bell was placed in a jar containing a vacuum. You could see the bell being struck,
but you could hear no sound because there was no medium to transmit sound from the bell to you. Now
lets look at another example in which the third element, the detector, is missing. You see a source (such
as an explosion) apparently producing a sound, and you know the medium (air) is present, but you are too
far away to hear the noise. Thus, as far as you are concerned, there is no detector and, therefore, no sound.
We must assume, then, that sound can exist only when a source transmits sound through a medium, which
passes it to a detector. Therefore, in the absence of any one of the basic elements (source, medium,
detector) there can be NO sound.
Q18. Sound waves transmitted from a source are sometimes weak when they reach the detector. What
instrument is needed to boost the weak signal?
TERMS USED IN SOUND WAVES
Sound waves vary in length according to their frequency. A sound having a long wavelength is heard
at a low pitch (low frequency); one with a short wavelength is heard at a high pitch (high frequency). A
complete wavelength is called a cycle. The distance from one point on a wave to the corresponding point
on the next wave is a wavelength. The number of cycles per second (hertz) is the frequency of the sound.
The frequency of a sound wave is also the number of vibrations per second produced by the sound source.
Q19. What are the three basic requirements for sound?
CHARACTERISTICS OF SOUND
Sound waves travel at great distances in a very short time, but as the distance increases the waves
tend to spread out. As the sound waves spread out, their energy simultaneously spreads through an
increasingly larger area. Thus, the wave energy becomes weaker as the distance from the source is
Sounds may be broadly classified into two general groups. One group is NOISE, which includes
sounds such as the pounding of a hammer or the slamming of a door. The other group is musical sounds,
or TONES. The distinction between noise and tone is based on the regularity of the vibrations, the degree
of damping, and the ability of the ear to recognize components having a musical sequence. You can best
understand the physical difference between these kinds of sound by comparing the waveshape of a
musical note, depicted in view A of figure 1-13, with the waveshape of noise, shown in view B. You can
see by the comparison of the two waveshapes, that noise makes a very irregular and haphazard curve and
a musical note makes a uniform and regular curve.
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