Sound Wave Properties Flashcards
velocity
• The speed (and direction) of sound
• Speed of acoustic waves varies with
•substance
•temperature
• elevation
• Speed of an electrical wave near light speed
Velocity of Sound
Velocity of Sound
• The speed of sound is 1130 ft/s (feet per
second) in average humidity and at 70º F.
• 770.5 miles per hour
• 343 meters per second
• You’ll find the ft/s or meters/second (m/s)
measurement used for wavelength calculations.
Velocity in Various Substances
•Velocity Of Sound in Various Substances
•Air @ 0 degrees C = 1087 fps
•Air @ 20 degrees C = 1,130 fps
•Helium @ 20 degrees C = 3,040 fps
•Water @ 15 degrees C = 4,714 fps
• Steel = 16,400 fps
The wavelength (λ)
The wavelength (λ) is the distance it takes for one cycle to complete
Calculating the Wavelength
λ = V/F
V- Velocity
F- Frequency
A 1 kHz (1000 Hz) has a wavelength of 1.13 feet.
1130 ft/s ÷ 1000 Hz = 1.13 ft
Hertz (Hz) = cps or cycles per sec
acoustical phase
A phase relationship is a time relationship between
two waves of similar frequency and amplitude
• Phase is measured in degrees (ø)
Out of Phase
•If two waves of similar frequency and
amplitude but out of phase are combined then:
•Destructive Interference
• Phase cancellation
• Constructive Interference
• Increased amplitude
Phase Cancellation
180 Degree
Shift
Constructive Interference
• Increased amplitude
Destructive Interference
Phase cancellation
•sine wave (pure tone)
It is a pure tone—a single frequency devoid of harmonics and
overtones.
Sine wave gets its name for the trigonometric
function
• Sine waves are the basic building blocks of all non
impulse sounds
waveform
Simple Shapes
• Sine
• Square
• Triangle
• Saw-tooth
timbre
Each sound has a unique tonal mix of fundamental and harmonic frequencies that distinguishes it
from all other sound, even if the sounds have the same
pitch, loudness, and duration. This difference between
sounds is what defnes their timbre—their tonal quality,
or tonal color.
The number and amplitude of harmonics shape the
timbre
harmonics
exact multiples of the fundamental;
and its overtones, also known as inharmonic overtones,
are pitches that are not exact multiples of the fundamental. If a piano sounds a middle C, the fundamental is
261.63 Hz; its harmonics are 523.25 Hz, 1,046.5 Hz, and
so on; and its overtones are the frequencies in between
(see 2-12). Sometimes in usage, harmonics also assume
overtones.
•Harmonics are overtones of a fundamental
frequency
• The number and amplitude of harmonics shape the
timbre
•Wave shape and harmonic content are
interdependent
• Fourier analysis can break down sounds into their
sine wave components
partials or overtones
•An overtone is a partial (a “partial wave” ) that can
be either a harmonic partial (a harmonic) other
than the fundamental, or an inharmonic partial.
•A harmonic overtone is an integer (whole number)
multiple of the fundamental frequency.
•An inharmonic overtone is NOT a whole number
multiple of the fundamental frequency
Sound Envelope
Another factor that infuences the timbre of a sound is
its shape, or envelope, which refers to changes in loudness over time. A sound envelope has four stages: attack,
initial decay, sustain, and release (ADSR). Attack is how
a sound starts after a sound source has been vibrated.
Initial decay is the point at which the attack begins to
lose amplitude. Sustain is the period during which the
sound’s relative dynamics are maintained after its initial
decay. Release refers to the time and the manner in which
a sound diminishes to inaudibility (see 2-13).
• The internal dynamics of a sound
• Changes in amplitude over time
• Four parts
•Attack
•Decay
• Sustain
•Release
