sound: properties and functions

04/20/23 Tech I Lighting Unit 1

Sound: Properties and Functions

Technical Theatre I


Introduction to Sound Acoustics is the science that deals

with the production, control, transmission, reception, and effects of sound; the study of sound

The students will learn the properties of sound and its applications in theatre

Understanding sound is essential to sound design


Properties of Sound (the Science)

Sound is a vibration of a medium

Medium – a material that transmits energy

Speed varies depending on pressure, temperature 1129 ft/sec, 770 mi/hr in air, 4708 ft/sec, 3210 mi/hr in

water 3.17 mi/sec in steel

What we hear is based on perceived vibrations


Measuring Sound Sound travels in waves

(sound waves), which are transferences of energy via rapid changes in the density of a medium

Sound waves are measured by speed, wavelength, amplitude, and frequency


Measuring Sound (Wavelength)

Wavelength (λ)– the distance between repeating units of a wave pattern; the distance from one crest to the next repeated crest, or one trough to the next repeated trough

λ of a 10,000Hz sound –> 1.35 inches λ of a 188Hz sound –> 6 feet


Measuring Sound (Amplitude)

Amplitude – (A) the distance of the crests and/or troughs of a waveform from the neutral line

Amplitude in sound waves is representative of intensity, or Volume (loudness)

Volume is measured in decibels (dB, or deci-Bells), a logarithmic scale <85 dB is considered harmful <95 dB can cause permanent

damage if exposed for prolonged periods

<125 dB can cause instant hearing damage


Measuring Sound (Frequency) Frequency – (f) the number of

occurrences of a repeated event per unit of time; pitch

Usually measured in occurrences per second, or Hertz (Hz)

Human hearing is usually represented as being “20 to 20,” i.e. 20 Hz to 20,000 Hz (or 20kHz)

Our hearing is typically more like 22 Hz to 18kHz, and continues to decrease as people age

Frequencies (Do you hear what I hear?)


440 Hz 1000 Hz 1500 Hz 2 kHz 4 kHz 8 kHz 14 kHz

15 kHz 16 kHz 17 kHz 18 kHz 19 kHz 19.5 kHz


Adding Frequencies

Adding two identical frequencies in the same phase reinforces the sound

Adding two identical frequencies 180° out of phase cancels out the sound


Adding Frequencies (continued)

Adding two different frequencies results in a different frequency, reinforced in some places & cancelled in others

Timbre and Harmonics

Few sounds are pure tones; most sound is made up of a combination of frequencies and amplitudes

Timbre - /tam’-bər/ a quality given to a sound by its overtones (harmonics)

Harmonic – a frequency that is an integral multiple of the fundamental


Perception of Sound

Distance – decreases the volume (the Inverse Square Law); air absorbs higher frequencies

Loudness – humans hear 2k-4k Hz best, thus this range is perceived loudest

Masking – one sound obscured by others; lower usually masks higher



Functions of Sound in Theatre Sound Effects – (FX) used to illustrate

ideas in a play or establish ambience, i.e. radios, explosions, trees rustling in the wind, crickets at night, sounds of machinery in a manufacturing plant

Underscoring – music used to establish or reinforce mood

Live Reinforcement – microphones used to boost the loudness of existing sound(s)

04/20/23 Tech I Sound Unit 14

The Path of Sound Source – can be live or pre-recorded

Microphones, pick-ups, synthesizers Or CD, tape, MD, mp3 or other computer file

type, record, etc. Amplifier – adds power to source signal,

boosts mic, instrument, or line level to speaker level Processor – can affect signals with effects or

ehancements Output – either speaker or recording

device

Input sources:


Patch Panel

Synthesizer Computer CD

Crossover

Delay

Compressor

Effects Processor

Equalizer

Mixing Console

Amplifier

Amplifier

Microphone


Input sources: -Microphones
