AUDIO &
ACOUSTICS
THEORY
Week 2
Sound Physics, Ranges of Hearing
Frequency, Wavelength, Period, Velocity
Audio Engineering & Sound Production
Unit code: AUD202
Sound is Vibrations
When an object vibrates it causes nearby
molecules to vibrate causing a chain
reaction
Sound is Vibrations
Sound travels as a series of compressions
and rarefactions through a medium
Sound is a Mechanical Wave
Sound travels through air as a longitudinal
wave
However it can also travel as a transverse wave
(such as on a guitar string or a wave in water)
One complete cycle is one compression
and one rarefaction
1000 cycles per second = 1000Hz = 1kHz
Sine Wave
The sine wave is a pure tone with no harmonics
Simple Waveforms
Sine
Square
Triangle
Sawtooth
HIGHER FREQUENCY
shorter wavelength
LOWER FREQUENCY
longer wavelength
Frequency range of hearing
The typical range of hearing of a young
undamaged ear is between 20Hz and
20kHz
A3 = 220 Hz
A4 = 440 Hz
A5 = 880 Hz
C4 = 261.6 Hz
D4 = 293.7 Hz
E4 = 329.6 Hz
F4 = 349.2 Hz
G4 = 392 Hz
A4 = 440 Hz
B4 = 493.9 Hz
C5 = 523.2 Hz
Dynamic Range of Hearing
The typically accepted amplitude range of
human hearing is 120dBSPL
Sound amplitude is referenced to the
Pascal (Pa) (the unit for pressure)
0dBSPL = 0.00002 Pascals (20
µPa)
120dBSPL = 20 Pascals
Dynamic Range of Hearing
60 decibels of amplitude
-60dBFS to 0dBFS
Units of Measurement
= period of one cycle (in seconds)
f
= frequency in Hertz (Hertz is cycles per second)
 = wavelength
v = velocity of sound
(in metres)
(in metres per second)
Velocity of Sound Formula
v = 331.4 + (0.6x°C)
The velocity of sound through air
at 21 degrees Celsius is 344m/s
THE SOUND
BARRIER
THE SOUND
BARRIER
The Sound Barrier
SPEED OF SOUND
344 m/s
1482 m/s
5200 m/s
12000
m/s
AIR
WATER
STEEL
DIAMON
D
The Decibel
The Bel is named after Alexander Graham
Bell 1847 –1922.
The decibel (dB) is a tenth of a Bel
Amplitude is measured in decibels
Loudness is Subjective
Amplitude is Objective
Loudness
Loudness is a
subjective term
describing the
strength of our
perception of
sound.
Loudness is measured in Phons
Threshold of Pain 120dB
Threshold of hearing is