The Science of Sound and Its Application in Theater
1. Definition of Sound
Sound is produced when a body at rest is made to vibrate, causing pressure waves to move in all directions from the source.
2. Wavelength
The distance between successive crests of a wave, especially points in a sound wave or electromagnetic wave.
3. Frequency
The rate at which a sound vibrates measured in cycles per second or hertz (Hz). The length of a sound wave determines frequency. A sound’s frequency determines its pitch.
4. Intensity
The actual or comparative brightness of light.
5. Harmonics
The overtones that are created when a note is played on a musical instrument. Normally, these are multiples of the fundamental frequency.
6. How the Ear Hears Sound
Sound waves travel into the ear canal until they reach the eardrum. The eardrum passes the vibrations through the middle ear bones, or ossicles, into the inner ear. The inner ear is shaped like a snail and is also called the cochlea. Inside the cochlea, there are thousands of tiny hair cells. The Pinna acts like an antenna to collect sound waves and directs them to the ear canal. The Tympanum vibrates in reaction to the sound.
- The middle ear contains 3 tiny bones referred to as the Stirrup, Hammer, and Anvil that take up and intensify these vibrations.
- The inner ear (Cochlea) houses many nerve endings that receive pressure from vibrations through tiny hair-like cells.
7. How the Brain Perceives Sound
Responding to the pressure, these nerves send electromechanical signals via the auditory nerve to the brain for interpretation.
8. Localizing Sound
- Horizontally: We can figure out where sound is coming from.
- Vertically: It is hard to listen because of our ears.
9. Range of Human Hearing
20 Hz to 20,000 Hz.
10. Reverberation
The combination of multiple blended sound images caused by reflections from walls and other surfaces.
11. 8 Functions of Sound in Theater
- Transmit human voices/music.
- Establish locale.
- Establish atmosphere.
- Create/sustain mood.
- Independent stimuli.
- Function as a character.
- Reveal character.
- Advance the plot.
12. Sound Reinforcement
The electric amplification of actors or musical instruments on stage used to:
- Help the audience hear the actors.
- Blend and balance the vocals and instruments in a musical production.
- Add an effect or change the quality of voices.
13. Sound Reproduction
Electrical or mechanical inscription and re-creation of sound waves, such as spoken voice, singing, instrumental music, or sound effects.
Live sound effects – (Props)
14. Decibels
The most common measure of amplitude, with 1 dB being the smallest difference that can be distinguished by the normal human ear. It is not on a linear scale.
1 dB = 1/10 of a Bel.
Signal Levels – the amplitude level of the desired signal.
Psychoacoustics
The scientific study of sound perception. More specifically, it is the branch of science studying the psychological and physiological responses associated with sound (including speech and music). The human ear can nominally hear sounds in the range 20 Hz (0.02 kHz) to 20,000 Hz (20 kHz). The upper limit tends to decrease with age; most adults are unable to hear above 16 kHz. The lowest frequency that has been identified as a musical tone is 12 Hz under ideal laboratory conditions. Tones between 4 and 16 Hz can be perceived via the body’s sense of touch.
- Digital Signal: Audio information represented by multiple binary measurements. An analog waveform is measured or sampled many times. The aggregate of those values represents the waveform.
- Analog Signal: Audio information represented by a continuous variable measurement of physical quantities such as length, voltage, or pressure. This signal is a continuous curve.
Digital Sound
Technology that can be used to record, store, generate, manipulate, and reproduce sound using audio signals encoded in digital form. Following significant advances in digital audio technology during the 1970s, it rapidly replaced analog audio technology in most areas of sound production, sound engineering, and telecommunications.
Sound System Equipment
Signal Sources
Microphone
They convert sound waves into electrical energy for transmission to another location.
- Omni – Receives sound from all directions. Used for: body mics, monitor mics, pressure zone mics.
- Bi-directional – “Figure 8” or bi-directional microphones receive sound equally from both the front and back of the element.
- Cardioid – The most common unidirectional microphone is a cardioid microphone, so named because the sensitivity pattern is a cardioid. The cardioid family of microphones are commonly used as vocal or speech microphones since they are good at rejecting sounds from other directions.
Tape Recorders
Audio storage device that records and plays back sounds, including articulated voices, usually using magnetic tape, either wound on a reel or in a cassette, for storage.
Types
- Magnetic Tape
- Analog
- Wire recorders
- Digital
Digital
A digital voice recorder is a small hand-held device that is used to record voice memos to a memory chip and play the memos back. It can also be used to record lectures, conferences, or conversations. Standard DVRs are not intended for recording music, as the sampling rate is lower than what is normally used for quality musical reproduction.