hearing, for it aids in the comprehension of the ideas being transmitted. It also helps any listener to concentrate on
conversations taking place amid sources of distraction, such as other conversations or unusual noise.
Conversation by Telephone.
The relatively low power of speech sounds limits the maximum distance over which individuals may conduct
face-to-face conversation. An attempt to converse at greater distances usually results in a lower degree of intelligibility.
For communication over greater distances, some other means of transmitting the voice is required, and the telephone is the
simplest device for this purpose. However, although the telephone succeeds in performing this primary function, its
operation presents some rather complex problems which do not occur in transmission of sound through air. These
problems include distortion of the sound, noise generated mechanically and electrically in the telephone system, noise
from external sources, the cutting off of some of the low and high-frequency components of the sound, and the reduction
in volume (attenuation) which occurs in long-distance transmission. All of these problems tend to reduce the
intelligibility of the words, the naturalness of the tone, and quality of the sound. They arise from the wires, from the
component parts of the equipment, and from the associated circuits required for the generation of power. The engineer
must take account of these problems in designing telephone equipment, and both the operator and the maintenance man
must be familiar with them to secure the best possible operation of the equipment. Particularly, distortion of sound and
distraction from external sources must be kept at a minimum since personal contact, so important in face-to-face
conversation, is lacking.
a. Sound waves are caused by the vibration of a rigid or semirigid body.
b. The transmission of sound always requires a medium; the transmission of light or electromagnetic waves does
not require a medium. Air is usually the medium for sound transmission, but either liquid or solid mediums can be used.
c. Vibrating bodies set up alternate condensations and rarefactions in adjacent groups of air particles. These
particles transfer their motion in turn to the next group, and this continuing action produces a wave of energy.