2 physics of sound

Reverberance Reverb 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

Physics of Sound

Part 1

Sound waves How they are generated and

travel

Sound Waves

 Generation and Propagation

 Sound wave = changes in pressure caused by

vibrating object

 Compression = High pressure

 Rarefaction = Low pressure

 Sound needs a medium to “vibrate”

 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

 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

 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

 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

Measuring methods

 Frequency will determine pitch

 High frequency = high pitch

 Low frequency = low pitch

 Octave – a doubling of halving of the frequency

Measuring methods

 Human hearing range

 Low range between 15 to 30 Hz

 With enough power lower than 15 Hz can be felt, but not heard as “sound”

 High range varies with age and gender

 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

 Traditional orchestra would tune First Chair Violin A first.

 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

 Corresponds to the 49 th 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

Measuring methods

 Amplitude

 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

 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

 Phase

 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

Standing waves

 When sound waves bounce off

of obstructions, they can

interfere with themselves

 Tends to reinforce some

frequencies and attenuate

Reverberance (Reverb)

 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

 Controlling reflections can reduce or increase reverb time

 Air tends to absorb frequencies above 2K Hz

 Sight line obstructions

 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

 Intimacy – Indicates the size of a room

 How it sounds to the listener, not actual size

 Determined by the initial-time-delay-gap (ITDG)

 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

 Related to Reverberance

 Room size is related

 More reflections is live Less reflections is dry or dead

Acoustic attributes

 Loudness of direct sound

 Inverse square law

 Loudness of sound will decrease by one quarter every time the distance from the source is

doubled

 Definition or Clarity

 Good definition when sound is clear

 Related to intimacy, liveness, loudness of direct and reverberant sound

Acoustic attributes

 Brilliance

 A hall that has liveness, clarity and intimacy

 Diffusion

 Relates to the orientation of reverberant sound

 Where is the reflected sound coming from

 It is preferable to have reverb sound coming from all directions

 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 is a measurable quantity

 SPL – Sound Pressure Level

 dB – deciBel

 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

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

 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

 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

 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 .)

 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

 Choreography

 Music cues

 Reinforcement of foot fall (Mic cues for tap dancing)

 Music monitoring for dancers

Use of Sound in the Theatre

What Audience Hears – Company Hears

 Elements that are part of the show

 What an audience hears

 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

 Mechanical – 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

Use of Sound in the Theatre

What Audience Hears – Company Hears

 Reinforcement of aural elements of

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

Paper work, paper work, paper work….

Paper work, paper work, paper work….

Paper work, paper work, paper work….

For Next Class

 The Spaghetti Factor!, Coleman