What is Sound?

Question 1

Sound Provides more Information

Answer 1

• Try watching a program or film without the sound.
• Then close your eyes and only listen to the sound.
On average, the sound alone provides more of the
storyline than visual alone.

Question 2

Sound

Answer 2

• Anything with mass can be caused to vibrate by the
input of energy.

• String
• Drum head
• Column of air
• A room

Question 3

Resonant Frequency

Answer 3

• The vibration will be at the resonant frequency
• The resonant frequency is the preferred or natural
frequency of vibration for that object
• The resonant frequency will depend on the mass
and the elasticity of the matter
• Overtones of the resonant frequency will also be
present

Question 4

Transverse wave

Answer 4

• The energy traveling through the string is creating a
transverse wave.
• The motion of the string is vertical, moving up and down
• The motion of the wave is horizontal traveling left and right.

Examples:
• Vibrating string
• Vibrating drum
• Something that when
struck or plucked
vibrates at it’s resonant
frequency

Question 5

The Vibrating String Generates
Sound Waves

Answer 5

• The vibrations of the string will be transmitted into
surrounding medium (air) as pressure waves
• Compression
• An increase in atmospheric pressure
• Rarefaction
• A decrease in atmospheric pressure

Question 6

Longitudinal Wave

Answer 6

• The energy traveling through the medium of air is longitudinal
• The particles oscillate or vibrate in the same direction as the
movement of the wave.

Examples:
• Sound traveling
through a medium like
air or water
• Vibrations in a column
of air like a flute or
horn that vibrate at
their resonant
frequency

Question 7

sound wave

Answer 7

a vibrational disturbance that involves
mechanical motion of molecules transmitting energy from
one place to another.

Question 8

sound wave is caused when

Answer 8

object vibrates and sets
into motion the molecules nearest to it; the initial motion
starts a chain reaction. This chain reaction creates pressure
waves through the air, which are perceived as sound when
they reach the ear and the brain.

Question 9

The pressure wave

Answer 9

compresses molecules as it moves outward, increasing pressure, and pulls the molecules farther
apart as it moves inward, creating a rarefaction by decreasing pressure.

Question 10

The components that make up a sound wave are

Answer 10

frequency,
amplitude, velocity, wavelength, and phase.

Question 11

sound

Answer 11

Sound acts according to physical principles, but it also has
a psychological effect on humans.

Question 12

frequency, or pitch

Answer 12

The number of times a sound wave vibrates

Humans can hear frequencies between roughly 20 Hz (hertz) and 20,000 Hz—a range of
10 octaves. Each octave has a unique sound in the frequency spectrum.

• Measured in cycles per second
• c.p.s. = Hertz = Hz.
• f = 1/T where “T” is the time or period of one cycle
• Note that frequency and period are reciprocal
• T=1/f

Question 13

amplitude, or loudness

Answer 13

The size of a sound wave - vertical/Hight

Loudness is measured in decibels.

The number of molecules in motion, and therefore the
size of a sound wave

Question 14

The decibel (dB)

Answer 14

dimensionless unit used to compare
the ratio of two quantities usually in relation to acoustic
energy, such as sound-pressure level (SPL).

The decibel (dB) is a dimensionless unit and, as such, has
no specifcally defned physical quantity. Rather, as a unit
of measurement, it is used to compare the ratio of two
quantities usually in relation to acoustic energy, such as
sound pressure, and electric energy, such as power and
voltage (see chapter 6). In mathematical terms it is 10
times the logarithm to the base 10 of the ratio between
the powers of two signals:

Question 15

dynamic range

Answer 15

Humans can hear from 0 dB-SPL, the threshold of hearing;
to 120 dB-SPL, the threshold of feeling; to 140 dB-SPL, the
threshold of pain, and beyond. The scale is logarithmic,
which means that adding two sounds each with a loudness
of 100 dB-SPL would bring it to 103 dB-SPL. The range of
difference in decibels between the loudest and the quietest
sound a vibrating object makes is called dynamic range.

Question 16

equal loudness principle

Answer 16

The ear does not perceive all frequencies at the same loudness even if their amplitudes are the same. This is the equal
loudness principle. Humans do not hear lower- and higher pitched sounds as well as they hear midrange sounds.

Question 17

Masking

Answer 17

covering a weaker sound with a stronger sound
when each is a different frequency and both vibrate simultaneously—is another perceptual response that depends on
the relationship between frequency and loudness.

Question 18

Velocity

Answer 18

Velocity—the speed of a sound wave—is 1,130 feet per
second at sea level at 70°F (Fahrenheit). Sound increases
or decreases in velocity by 1.1 feet per second for each
1°F change.

Question 19

wavelength

Answer 19

Each frequency has a wavelength, determined by the distance a sound wave travels to complete one cycle of compression and rarefaction. The length of one cycle is equal
to the velocity of sound divided by the frequency of sound.
The lower a sound’s frequency, the longer its wavelength;
the higher a sound’s frequency, the shorter its wavelength.

Question 20

Acoustical phase

Answer 20

Acoustical phase refers to the time relationship between
two or more sound waves at a given point in their cycles.
If two waves begin their excursions at the same time, their
degree intervals will coincide and the waves will be in
phase, reinforcing each other and increasing amplitude. If
two waves begin their excursions at different times, their
degree intervals will not coincide and the waves will be out
of phase, weakening each other and decreasing amplitude.

Question 21

Timbre

Answer 21

Timbre is the tone quality, or tone color, of a sound.

Question 22

sound envelope

Answer 22

A sound’s envelope refers to its changes in loudness over
time. It has four stages: attack, initial decay, sustain, and
release (ADSR).

Question 23

Analog Recording to Digital

Answer 23

In an analog system of recording, a physical sound wave is
transformed into an electric current or voltage by using an
electroacoustic transducer. Digital audio reproduces sound
using a technique called pulse-code modulation (PCM)
wherein the analog signal is transformed into binary data
that approximates the original.

Question 24

Human Ear

Answer 24

The human ear is divided into three parts: the outer ear,
the middle ear, and the inner ear.

Question 25

sound from the ear to the brain

Answer 25

In the basilar membrane of the inner ear are bundles of microscopic hairlike projections called cilia attached to each
sensory hair cell. They quiver at the approach of sound and
begin the process of transforming mechanical vibrations
into electrical and chemical signals, which are then sent to
the brain.

Question 26

Temporary threshold shift (TTS), or auditory fatigue

Answer 26

Temporary threshold shift (TTS), or auditory fatigue, is a
reversible desensitization in hearing caused by exposure to
loud sound over a few hours.

Question 27

Hearing damage

Answer 27

Prolonged exposure to loud sound can bring on tinnitus,
a ringing, whistling, or buzzing in the ears.

Question 28

Permanent hearing damage

Answer 28

Exposure to loud sound for extended periods of time can
cause permanent threshold shift—a deterioration of the
auditory nerve endings in the inner ear. In the presence of
loud sound, use an ear flter (hearing-protection device)
designed to reduce loudness.

Question 29

Compression

Answer 29

For an acoustic wave, an increase
in air pressure above normal (+)

Increase in Amplitude above normal

Question 30

rarefaction

Answer 30

For an acoustic wave, a decrease in air pressure below normal (-)

Decrease in amplitude below normal

Question 31

kilohertz (kHz)

Answer 31

Hz * 0.001 = kHz
or /1000

if it completes 10,000 cps, its frequency
is 10,000 Hz, or 10 kilohertz (kHz)

Question 32

pitch

Answer 32

Psychologically, and in musical terms, we perceive
frequency as pitch—the relative tonal highness or lowness of a sound. The more times per second a sound
source vibrates, the higher its pitch.

Question 33

range of human
hearing

Answer 33

20 Hz to 20 kHz

Question 34

bandwidth

Answer 34

The term bandwidth refers to a range of
frequencies.
• The bandwidth of human hearing is 20 Hz – 20 kHz
• Bandwidth is referred to as frequency band
• An octave is a band of frequencies.
• Speakers and equipment have bandwidth
specifications that define the lowest and highest
frequency they can reproduce accurately.

Question 35

Octave

Answer 35

An octave is the interval (band of frequencies) between any two frequencies that have a tonal ratio of 2:1

Question 36

Low bass

Answer 36

– 1st and 2nd octaves (20 to 80 Hz)

Question 37

Upper bass

Answer 37

3rd and 4th octaves (80 to 320 Hz)

Question 38

Midrange

Answer 38

5th, 6th, and 7th octaves (320 to 2,560 Hz)

Question 39

Upper Midrange

Answer 39

8th octave (2,560 to 5,120 Hz)

Question 40

Treble

Answer 40

9th and 10th octaves (5,120 to 20,000 Hz)

Question 41

sound pressure level (dB-SPL)

Answer 41

Acoustic sound pressure is measured in terms of soundpressure level (dB-SPL) because there are periodic variations in atmospheric pressure in a sound wave. Humans
have the potential to hear an extremely wide range of
these periodic variations, from 0 dB-SPL, the threshold
of hearing; to 120 dB-SPL, what acousticians call the
threshold of feeling; to 140 dB-SPL, the threshold of pain,
and beyond

A sound-pressurelevel change of 1 dB increases amplitude 12 percent; an
increase of 6 dB-SPL doubles amplitude; 20 dB increases
amplitude 10 times. Sound at 60 dB-SPL is 1,000 times
louder than sound at 0 dB-SPL; at 80 dB-SPL it is 10
times louder than at 60 dB-SPL. If the amplitude of two
similar sounds is 100 dB-SPL each, their amplitude,
when added, would be 103 dB-SPL. Nevertheless most
people do not perceive a sound level as doubled until it
has increased anywhere from 3 to 10 dB, depending on
their aural acuity.
There are other acoustic measurements of human
hearing based on the interactive relationship between
frequency and amplitude.

Question 42

the threshold
of hearing

Answer 42

0 dB-SPL

Question 43

threshold of feeling

Answer 43

to 120 dB-SPL

Question 44

threshold of pain

Answer 44

140 dB-SPL