Consonant sounds are usually produced without the aid of the vocal cords. Most of these sounds are produced by the lips and teeth, as in the pronunciation of "th,""s," and "f." The range of frequencies covered by consonant sounds is from 200 to 8000 cycles, but most consonant sounds have frequencies of less than 6000 cycles.

9. Hearing. The actual mechanism of hearing is not very well understood, but certain facts regarding the ability of the ear to register sounds of various frequencies has been determined very accurately. The range of frequencies which the average person can hear is from about 20 cycles to 17,000 cycles, but a comparatively large amount of sound energy is required before the ear can detect sound of extremely low or extremely high frequencies. The ear is most sensitive to frequencies between 500 cycles and 7000 cycles; also, the ear is most sensitive to changes of pitch and changes of intensity of sound in this same band of frequencies.

(B) SOUND AS A FORM OF ENERGY

10. Matter and Energy. The recording and reproduction of sound involves the use of energy in many forms, and matter in general. Everything with which we come in contact in our daily life is in some way related to energy and matter.

Matter is anything which has size, shape and weight, that is, anything capable of occupying space. All matter is believed to consist of small particles, called molecules, which are in rapid motion, but travel only through very short distances. Matter is believed to hold its shape due to the mutual attraction of the particles.

There are three classes of matter, solids, liquids and gases. In solids the particles are relatively close together and, although the particles are in motion, the motion is of a very orderly nature, and considerable force is required to separate them or change the order of their motion. In liquids the motion of the particles is still very orderly, but the particles slide over each other with less difficulty, and they move at greater speeds than do the particles of solids. In gases the particles move more or less at random, and can be considered as knocking one another around, which gives the gas a tendency to expand as pressure is released. The gases of the air are compressed by the weight of the air above, and as we go farther up from the surface of the earth the air is less dense.

Energy is work, anything that arises as the result of work, or anything which can be converted into work. Such a statement is not clear in itself, but it will serve as a starting point for a discussion of energy. For greater clarity, energy can be classified into many different forms, the most common of which are mechanical energy, sound energy, heat energy, electrical energy, light energy and chemical energy.

Energy cannot be created or destroyed, but one form of energy can be converted to other forms. A good example of the conversion of energy from one form to others is the generation and use of electrical energy. The energy of coal is chemical. When coal is burned the chemical energy is transformed to heat energy, which changes water to steam. The steam confined in a boiler builds up a pressure. This steam under pressure is used to drive turbines mechanically coupled to the generators which convert the mechanical energy to electrical energy for distribution.

The electrical energy is converted into various forms as required, such as heat energy to heat flat irons, water heaters, waffle irons, etc.; mechanical energy by electric motors for driving various machines, trains, etc.; light energy for artificial lighting; or into chemical energy for plating metals, charging storage batteries, etc.

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