Chapter 10: Sound And The Ears Flashcards
Sources of Sound
In order:
- Sound is initiated by movement that disturbs air molecules
- Molecules collide with other air molecules resulting in air pressure that propagates outward from source
- As the sound wave travels outward form the source in all directions, the wave front resembles a sphere that grows continuously larger
- Sound energy at any given point on the wave from decreases with distance from the source (inverse square law)
Sound Waves
Waves of pressure changes in air caused by vibrations of a source
Cycle
In sound wave, a repeating segment of air pressure changes
Inverse square law
Energy of sound decreases in proportion to square of distance from source
3 physical dimensions of sound:
- Frequency- pitch
- Amplitude- loudness
- Waveform- timbre
Periodic Sound Waves
Waves in which the cycles of compression and rarefaction repeat in regular (periodic) fashion
Pure Tone
Sound wave in which air pressure changes over time according to sine wave (sinusoid)
Frequency
Physical dimension of sound that is related to perceptual dimension of pitch
- expressed in hertz (number of cycles/ second of periodic sound wave)
Pitch
Perceptual dimension of sound that corresponds to physical dimension of frequency
- perceived highness/ lowness of sound
Hertz (Hz)
- physical unit used to measure frequency
- cycles per second
Amplitude
Difference between maximum and minimum sound pressure in sound wave
- physical dimension of sound that is related to perceptual dimension of loudness
Loudness
Perceptual dimension of sound that corresponds to physical dimension of amplitude
Decibels (dB)
- physical unit used to measure sound amplitude
- logarithmically related to sound pressure measured in micropascal
Waveform
Physical property for perceptual correlate for timbre
Periodic sound waves
Waves in which the cycles of compression and rarefaction repeat in a regular, or periodic, fashion
Compression
Region in a longitudinal wave where the particles are closest together
Rarefaction
Region in a longitudinal wave where the particles are furthest apart
- follows period of compression
Frequency and pitch
- the frequency of a pure tone is the physical dimension related to the perceptual dimension of pitch and expressed in hertz (Hz)
- Young human adult sound detection range: 20- 20000 Hz
- The loudest sounds a human can hear are approximately 1 million times the amplitude of the softest sounds that can be heard
Amplitude and Loudness
- Amplitude: expressed as dB SPL= 20 log (p/po)
- Loudness: perceptual dimension of sound that is related to physical dimension of amplitude
- how intense or quiet a sound seems
Audibility Curve
- shows minimum amplitude at which sounds can be detected at each frequency
- horizontal axis of this graph uses a logarithmic scale to allow the clear presentation of a wide range of frequencies
Equal Loudness Contours
Curve showing amplitude of tones at different frequencies that sound about equally loud
Phon
Unit of loudness
- loudness of tones is numerically equal to amplitude of 1000 Hz tones that sound equally loud
Fourier
Provided that waveforms of most periodic sounds have a more complex shape than a sine wave
- Fourier analysis
- Fourier spectrum
- Fundamental frequency
Fourier Analysis
Mathematical procedures for decomposing a complex waveform into collection of sine waves with various frequencies and amplitudes