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Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles....

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•Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old. •Some animals use for survival sound with frequencies too high for humans to hear. Bats, in particular, hunt flying insects by emitting pulses of very high-frequency sound. They learn how far away the insect is, how large it is, where it is, and what its relative velocity is. •Sound and music are important components of the human experience.
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Page 1: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

•Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

•Some animals use for survival sound with frequencies too high for humans to hear. Bats, in particular, hunt flying insects by emitting pulses of very high-frequency sound. They learn how far away the insect is, how large it is, where it is, and what its relative velocity is.

•Sound and music are important components of the human experience.

Page 2: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

The velocity of the sound wave in air depends on the temperature of the air. Sound waves move through

air at sea level at a velocity of 343 m/s at room temperature (20°C). Sound can also travel through

liquids and solids. In general, the velocity of sound is greater in solids and liquids than in gases. Sound

cannot travel through a vacuum because there are no particles to move and collide. The speed in air

increases 0.6 m/s for each °C increase.

Page 3: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

FIGURE 15-2. In an anechoic chamber, used for acoustical research, sound is almost completely absorbed by the soft materials covering all the

surfaces

Page 4: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

Relationship between velocity, wavelength and frequency

Page 5: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

A moving source “compresses” the waves on

the side it is moving towards

A wave tank demonstration

Doppler Effect Applet

A real Shock Wave

Page 6: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

 

The physical characteristics of sound waves are measured by frequency, wavelength, and amplitude. In

humans, sound is detected by the ear and interpreted by the brain. Sound characteristics are defined in terms describing what we perceive. Pitch is essentially the frequency of the wave. Loudness depends on the

amplitude of the pressure variation wave.

Page 7: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

The human ear is extremely sensitive to the variations in air pressure in sound. It can detect wave amplitudes of less than one billionth of an atmosphere (or 2 x 10-5 N/m2).

At the other end of the audible range, the pressure variations that cause pain are one million times greater, (20 N/m2). Notice that this is still less than one one-thousandths of an atmosphere.

Page 8: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

Because of this wide range in pressure variation, sound pressures are measured by a quantity called sound level. Sound level is measured in decibels (dB). The level depends on the ratio of the pressure of a given sound wave to the pressure in the most faintly heard sound, 2 x 10-5 N/m2. Such an amplitude has a sound level of zero decibels (0 dB). A sound with 10 times larger pressure amplitude (2 x 10-4 N/ m2) is 20 dB. A pressure amplitude 10 times larger than this is 40 dB. Figure 15—5 shows the sound level in decibels for a variety of sounds.

Page 9: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

Marin Mersenne (1588—1648) and Robert Hooke (1635—1703) first connected pitch with the frequency of vibration. Pitch can also be given the name of a note on a musical

scale. Musical scales are based on the work of Pythagoras, a Greek mathematician who lived in the sixth

century B.C. He noted that when two strings had lengths in the ratio of small whole numbers, for example 2:1, 3:2, or

4:3, pleasing sounds resulted.

Page 10: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.
Page 11: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

The shapes of the mouthpieces of a brass instrument (a) and a reed instrument (b) help

determine the characteristics of the sound each instrument produces

Page 12: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

In all the instruments

illustrated, changes in pitch are brought about by changing the length of the

resonating column of air.

Page 13: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

Resonance -- waves which add together to be louder

Page 14: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

Standing pressure waves resonating in

closed pipes. The first three harmonics are

shown.

Page 15: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.
Page 16: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.
Page 17: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

 The human ear is a complex sense organ that translates sound vibrations into nerve impulses that are then sent to

the brain for interpretation.

Page 18: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

Continuous exposure to loud sounds can

cause serious hearing loss. In many

occupations, workers such as aircraft line personnel and rock musicians wear ear

protection.

Page 19: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

Beats occur as a result of the

superposition of two sound waves of

slightly different frequencies.

Page 20: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.
Page 21: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

 

Musical instruments sound very different from one another, even when playing the same note. This is true because most sounds are made up of a number of frequencies. The quality of a sound depends on the relative intensities of these frequencies. In physical terms, it depends on the spectrum of the sound. In musical terms, sound quality is called timbre (TOM bur) or sometimes "tone color."

Page 22: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.
Page 23: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

The shape of the vocal tract determines the resonant wave forms for a as in sat (a) and u

as in suit (b).

Page 24: Primitive people made sounds not only with their voices, but also with drums, rattles, and whistles. Stringed instruments are at least 3000 years old.

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