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SPEECH, MUSIC, AND HEARING 249
greater sound pressures than those of the higher. The range of pressures for various instruments, however, is smaller for low notes, as has been determined by direct measurements of the pressures produced when the instruments are played by musicians. Contour lines for loud tones show a smaller change in pressure in going from low to high notes than do the contour lines for faint tones; so it would seem that music played faintly would cover a greater pressure range than loud music.
Percussion instruments, such as drums and the various accessory traps, produce the greatest pressures that are used in music. Although the fundamental frequency of the notes which they emit is fairly low, the complete notes are particularly rich in tones of higher frequency, extending as high as 10,000 cycles. Although these loftier tones die out rather rapidly, they are essential to good definition, or clearness. The organ, the piano, and the harp have the greatest span, covering a frequency range from about 16 to 4,000 cycles. All three of these instruments are characterized by a rather prominent first overtone, so that their effective range extends as high as 8,000 cycles.
Melody instruments, because of their limited range, are among the easiest to reproduce. In any given register, wind instruments produce greater intensities than strings, of which the violin produces the faintest. As a class, these instruments emit notes covering the frequency range of 32 to 4,000 cycles.
From our study of the auditory sensation area we have seen that the ear is able to perceive a large number of tones of different intensity and frequency. We have also seen that the voice and various musical instruments produce tones which cover a large portion of the auditory sensation area. In order to obtain information as to the relative importance of various parts of this area to the sensory characteristics of speech and music, experiments