Sound Waves And Their Sources (1950)

February 18, 2009 · By admin

Explains that all sound originates in vibrating objects and illustrates the three general types of vibrating sound sources. Describes the major characteristics of sound waves and demonstrates the principal auditory differences between sounds. Sound Waves and Their Sources; ; Contents. Sources of sounds and characteristics of sound waves, shown by means of oscilloscopes and animated diagrams.; ; As bass viol strings are shown vibrating, the commentator says that sound originates in vibrating objects that set up waves in surrounding air or in other mediums. A tuning fork is released, setting up sound waves in the air. Animation shows the resulting condensation and rarefaction of air surrounding the tuning fork. Longitudinal sound waves are shown, and the commentator says that the wave length is the distance between two adjacent regions of maximum condensation.; ; Means of measuring sound waves are demonstrated by a simplified diagram of an oscillograph in which alternate condensations and rarefactions cause a stylus to move up and down. Amplitude is demonstrated as sounds of varying loudness result in oscillograph recordings of varying heights. Frequency is described by the commentator as the number of complete vibrations a second. Tuning forks of different frequencies are used to demonstrate this fact. The oscillograph is used to demonstrate how two separate waves may unite to form a combined wave.; ; As a string vibrating in one segment is shown, the commentator says that only one tone called the “fundamental” or “first harmonic” is produced. This same technique is used to demonstrate second and third harmonics alone and a compound waveform in which the fundamental wave tone is supplemented by the second and third harmonics. Characteristics of saxophone and violin sounds are shown on the oscilloscope. Vowel sounds and noise characteristics are also shown.; ; As a vibrating diaphragm is shown, the commentator describes it as a source of sound. Another sound source, the vibrating column of air, is suggested by animated drawings of an organ pipe. The commentator briefly explains its operation. The human vocal system is shown in a cross-sectional diagram of the head. The vocal cords are shown in some detail. Animated drawings demonstrate the origin of speech as air is forced from the lungs through the glottis, causing the cords to vibrate.; ; As various views of sound sources in everyday life are shown, the commentator says that minute differences in sounds enable us to gather meaning from a complex maze of invisible vibrations.; ; Appraisal. Reported excellent for (1) showing the origin and transmission of sound waves and (2) demonstrating the fundamentals of the human voice. Should be useful in developing an appreciation of the instruments and techniques used in the study of sound.; ; Clear explanation of frequency, pitch, amplitude, and harmonics was reported. Use of animated diagrams and the oscilloscope made the presentation simple and effective. Teachers noted that the sound film was particularly well adapted to the subject.; ; Photography and sound are excellent.;