Physics of Sound
Part 1
Sound waves
How they are generated and
travel
Sound Waves

Generation and Propagation
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Sound wave = changes in pressure caused by
vibrating object
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Sound needs a medium to “vibrate”
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Compression = High pressure
Rarefaction = Low pressure
Usually air, but could be anything
Speed of sound depends upon the medium
Air = 1130 ft/sec
Water = 5000 ft/sec
Steel = 13000 ft/sec
Measuring sound waves

Sound waves are longitudinal waves
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Vibrating object compresses the air around it.
Pushes air away leaving an area of low pressure
Vibrating object then compresses more air to create a
“chain”
Measuring methods
Cycle

A single push and pull of the vibrating object
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One are of compression followed by one area of
rarefaction
An initial increase in atmospheric pressure from the
norm, followed by a drop below the norm and then a
return to normal
Mathematically displayed by a sine curve

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Pressure on Y axis
Time on X axis
Measuring methods
Period (T) and Frequency (f)
Period - The time it takes to create one cycle
 Frequency - The number of cycles in one second
1
f 
T
 Measured in Hertz (Hz) or cycles per second

Measuring methods
Example
It takes ¼ sec to create one cycle. What is
the sound wave’s frequency?
1
f 
 4 cycles per second
.25
Measuring methods
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Frequency will determine pitch
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High frequency = high pitch
Low frequency = low pitch
Octave – a doubling of halving of the
frequency
Measuring methods
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Human hearing range

Low range between 15 to 30 Hz

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With enough power lower than 15 Hz can be felt, but
not heard as “sound”
High range varies with age and gender
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Women - up to 20 kHz
Men – between 15 to 18 kHz
High frequency range will lower with exposure to high
levels of sound and age
Tuning

Traditional orchestra would tune First Chair Violin A first.
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Remaining instruments would tune relative to that
A above middle C was tuned to about 420 Hz
As halls grew larger it was found to be desirable to tune sharper
1939 A was established to be 440 Hz
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Corresponds to the 49th key on a full size piano
Tuning is not a science. The relative frequency difference is
what is important
Measuring methods
Wavelength
 The distance from one area of compression
to the next or one area of rarefaction to the
next
v

l=wave length
f
V = velocity of sound in medium
usually 1130 ft/sec
f = frequency
Measuring methods

Amplitude
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How high the pressure goes above and below
normal atmospheric pressure
Corresponds to how loud the sound is
“loudness” is relative to frequency and dependant
on the listener.
Timber and Harmonics
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Harmonics – multiples of a base frequency
Timber – the characteristics of a particular sound or
instrument

Different harmonics combined in different levels
Physics of Sound
Part 2
Basic Acoustics
Inverse square law
Reinforcement/cancellation
Interference

Phase
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measurement of where the amplitude of a wave is
relative to another wave
A cycle can start at any point in a waveform
Two waves with the same frequency can start at
different times
Measured as an angle in degrees

Related to the sine wave representation of the wave
Interference

Constructive of
destructive interference

Waveforms will add by
summing their signed
amplitude at each instant
in time
Beats
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Happens when two
slightly different
frequencies interfere
Often used in tuning
Standing waves
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When sound waves bounce off
of obstructions, they can
interfere with themselves
Tends to reinforce some
frequencies and attenuate
others
Prevented by using
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Non- Parallel walls, ceilings
Convex surfaces
Multi-level ceiling sections
Reverberance (Reverb)
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Consisting of multiple, blended sound images caused by
reflections from walls, ceilings and other structures which do not
absorb sound
NOT echo
 Echo consists of individual, non-blended sound images
Reverb time is related to
 The time it takes for a sound to reduce to an inaudible level
 Loudness of sound relative to background noise
 Ratio of loudness of reverberant to direct sound
Short reverb time (less than 1.5 sec) is better for speech or
drama
Long reverb time (more than 1.5 sec.) is better for music
Absorption

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Controlling reflections can reduce or increase reverb
time
Air tends to absorb frequencies above 2K Hz
Sight line obstructions
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Frequencies above 10 kHz tend to not bend around
corners well or other obstructions
 l=1.3 inches for 10 kHz tone
Frequencies below 1kHz do very well
 l=5.65 feet for 200 Hz tone
Specialists are often hired to “tune” a space
acoustically
Acoustic attributes
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
Defined by Leo Beranek after a 6 year study
of 54 concert halls
Used to define acoustic properties in terms
that other trained professionals can
understand
Acoustic attributes

Intimacy – Indicates the size of a room
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How it sounds to the listener, not actual size
Determined by the initial-time-delay-gap (ITDG)
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Interval between the sound that arrives directly at the
ear and the first reflection
Usually considered to be the most important
attribute
Acoustic attributes

Liveness
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Related to Reverberance
Room size is related
More reflections is live. Less reflections is dry or
dead
Warmth

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More low frequency sound relative to mid
frequency
Too much low frequency sound is said to be
“Boomy”
Acoustic attributes

Loudness of direct sound
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Inverse square law
Loudness of sound will decrease by one quarter
every time the distance from the source is
doubled
Definition or Clarity
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Good definition when sound is clear.
Related to intimacy, liveness, loudness of direct
and reverberant sound
Acoustic attributes

Brilliance
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A hall that has liveness, clarity and intimacy
Diffusion
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Relates to the orientation of reverberant sound
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Where is the reflected sound coming from
It is preferable to have reverb sound coming from
all directions
Intensity
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Like pitch, loudness is a sensation in the
consciousness of a listener
To produce a sound twice as loud requires 10
times the power
Inverse square law

Sound level is reduced by a factor of the square
of the distance away from the source

If you move double the distance from the source, the
sound intensity will by one quarter
Intensity

Intensity is a measurable quantity
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SPL – Sound Pressure Level
dB – deciBel
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A system of measuring a ratio between two powers
1dB change – Imperceptible change
3dB change – Barely perceptible
5dB change – Clearly noticeable
10dB change – About twice as loud
20dB change – About four times as loud
dB SPL
Sound
150 dB
Jet engine at 1m
140 dB
Rock and Roll stack at 1m
130 dB
Thunderclap, Air Raid Siren 1 Meter
120 dB
Jet takeoff (200 ft)
110 dB
Rock Concert
100 dB
Train passing up close
90 dB
Heavy traffic
80 dB
Hair Dryer
70 dB
City street
60 dB
Noisy bar or restaurant
50 dB
Open plan office environment
40 dB
Normal conversation level
30 dB
Library, Soft Whisper (5 Meter)
20 dB
Quiet domestic environment
10 dB
Broadcasting Studio, Rustling Leaves
0 dB
Threshold of hearing in young adult
Sound Envelope
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Listener does not hear individual cycles of sound waves
Attack – Time it takes for sound to rise from nothing to its
greatest intensity. Usually short.
Decay – Time it takes for a sound to fall from its attack level to its
sustaining level. Decay time is usually short
Sustain – The time during which the initial vibrating source
continues to supply energy to the sound. Usually perceived as
the duration and intensity of the sound
Release – Time it takes for the sound to drop from its sustain
level to inaudibility after vibrating object stops supplying energy
Sound Design

How, what and why of a show
Interaction of Sound
with other Show Elements

Script
Identification of motivational cues - sounds listed in
the script (cues that actors react to)
 Identification of environmental cue opportunities –
locations, time of day, season, era,
 Identification of emotional cue opportunities – What
do you want to say about actor, situation. . .

Interaction of Sound
with other Show Elements

Acting

Collaborate on what is “heard” on stage - Actors
need to understand what sounds are part of the
physical environment shared with the set and props.
Some
sounds are there for them to react to (Motivational)
Some sounds need to be originated by a performer’s
action (ring a bell, turn on a radio, etc...)
Monitoring of stage action to off-stage locations
 Placement of wireless mics and stage monitoring /
fold back
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Interaction of Sound
with other Show Elements

Costumes
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Musicals – wireless mics that need to be
accommodated within costumes and hair
Scenic
Location of on-stage devices (speakers, mics)
 Collaboration on scene shifts (needs/opportunities to
cover transitions using sound cues – “Functional”
sound cues)
 Identification of cues that support each other (sound
used to reinforce scenic element that would normally
make noise (car, train station, rain, etc. . .)

Interaction of Sound
with other Show Elements

Props
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“Active” on-stage devices that may be props
Lights
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Identification of cues that support each other
Thunder
and lightning,
Day time or night time,
Lights used to represent outdoors and other items/times
that would normally have a recognizable sound associated
with it.

Identification of transitions where cues should go
together
Interaction of Sound
with other Show Elements

Music direction
Vocal reinforcement (micing)
 Music reinforcement (micing, direct feeds and mixing)
 Vocal/music monitoring for performers and/or band
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Choreography
Music cues
 Reinforcement of foot fall (Mic cues for tap dancing)
 Music monitoring for dancers

Interaction of Sound
with Other Show Elements

Stage Management
Cueing
 Monitoring of stage action to booth
 Intercom systems
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Use of Sound in the Theatre
What Audience Hears – Company Hears

Elements that are part of the show

What an audience hears.
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Cues, Aural Reinforcement
Support for the Overall Production

What the company hears
Monitoring, Communications
 Recording

Use of Sound in the Theatre
What Audience Hears – Company Hears

Sound Cues - “created” sounds that
advance the story
Sound effects, music transitions and underscoring.
 Produced / reproduced through mechanical or
electronic means

– real sounds (sheet metal for thunder, crash
box for breaking glass, ½ coconuts for horse galloping,
actors making bird calls)
 Also called practical
Electronic reproduction
 Sounds stored as signals on CDs, Minidisks, computer
files
Mechanical
Use of Sound in the Theatre
What Audience Hears – Company Hears

Reinforcement of aural elements of
production
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Mic cues for vocal and musical performance
Orchestra Mics
Instrument direct feeds
Use of Sound in the Theatre
What Audience Hears – Company Hears

Monitoring – Providing performers and members of the
company a portion of the sound from the performance to assist
with their performance.
 Stage monitors for singers to hear the band – and
themselves – Fold back
 Pit monitors for band to hear vocals – and themselves
 House monitoring for crew positions, back stage and
dressing rooms so company can hear “what’s going on”
Use of Sound in the Theatre
What Audience Hears – Company Hears

Communications
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Intercoms for cueing and communications among the
company
Recording

Live feeds of performance for film, video and audio
recording
Paper work, paper work, paper
work….
SUFFOLK COUNTY COMMUNITY COLLEGE
SOUND CUE SHEET
Show:_________________________________________
Sem / Year _____/_____
Page _____ of _____
CUE
DEVICE INPUT CH
LEVEL
DEVICE OUTPUT CH
LEVEL
FADE TIME
NOTES
Paper work, paper work, paper
work….
CUE # Sound Cue
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
R
S
T
U
V
W
X
Y
Z
AA
BB
CC
DD
Preshow music
Preshow announcement
Preshow fade
Narrator
"Loser"
music cut
Awesome sound
Mission Impossible theme
music cut
Narrator
T.V.
T.V. fade
magic
fight music
music cut
Narrator into LL Cool J
"Waterfalls"
Voice Over
magic missle
Farrah explodes
Cheerleader enterance
music cut
cube eats
cube transforms
"Gonna Make you Sweat"
Footsteps
Tiamat Roar
Tiamat fight
Curtain call
Placement
At house opening
with house to half
with blackout
with lights up
with lights up
Chuck: "…the fuck!"
Agnes: "Go."
Agnes: "…the intro music!"
???
TOS
with lights up
Tilly: "…not good at all."
Agnes: "What are you doing?"
Chuck: "…what happens next - "
end of fight
Lilith: "…kicketh some ass."
with lights up
Tilly: "…Let's do this!"
with spell
Farrah: "Oh no."
Agnes: "…would be a bad thing, right?"
Steve: "…oh neat, a jello mold!"
Tilly: "…call it Miles."
Chuck: "…Cheerleaders!!!"
with blackout
with lights up
PG.
Type
7
7
7
7
9
9
13
14
14
18
18
19
23
24
24
26
28
29
29
29
34
34
47
49
59
69
69
69
71
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Called
Location
Cluster / BOH
Cluster
Cluster / BOH
Cluster
USC
USC
cluster
cluster
cluster
cluster
USC
USC
cluster
cluster
cluster
cluster
cluster
cluster
cluster
cluster
Cluster
Cluster
USC
Cluster
Cluster
SL
SL
SL
Cluster
Paper work, paper work, paper
work….
For Next Class

Read

The Spaghetti Factor!, Coleman

Patches and Facility Panels, Coleman
Soldering and Soldering 2 PDF


Study for Quiz 1