Sound

Front 1

sound energy

Back 1

changes in air pressure. when you clap, you compress air molecules into a higher density in the lower density air, creating a disturbance (colliding air molecules) that reaches your ears.

Front 2

rarefaction

Back 2

air molecules move further apart, disturbance travels outward

Front 3

compression

Back 3

air molecules move closer together

Front 4

pure tone

Back 4

sound stimulus in which pressure varies as a sine wave function of time (tuning fork)

Front 5

evaluation of continuous sounds

Back 5

continuous sounds can be viewed as a change in density of air molecules as a function of time OR a change in the density of air molecules as a function of distance from the sound source

Front 6

amplitude

Back 6

how much does the pressure change?

Front 7

wavelength

Back 7

how rapidly in time or space is the beginning on one cycle to the beginning of the next cycle. cycles per second. range 20 to 20,000 Hz

Front 8

white noise

Back 8

equal energy at all wavelengths

Front 9

producing sound: speakers

Back 9

movement of the speaker diaphragm creates a disturbance in the air

Front 10

noise-cancelling head phones

Back 10

microphones in the headphones pick up ambient noise and create out of phase noise (mirror, opposite image) so that's there's no change in air pressure. cushions on ears also block out high frequencies.

Front 11

fourier spectrum

Back 11

describes a sound at one instant in time. any sound can be represented by a number of sine waves added together. way of characterizing components of complex sound. freq, amplitude (lines)

Front 12

fundamental frequency

Back 12

lowest frequency component (sometimes called first harmonic)

Front 13

harmonics

Back 13

energy at exact multiples of fundamental frequency. Each of the higher-frequency simple waves is called a harmonic. In naturally occurring vibrations, there is a harmonic at each multiple of the fundamental
frequency -- theoretically all the way up to infinity, though they decrease in amplitude as frequency rises.

Front 14

amplitude equation

Back 14

amplitude=20 log (P/P0)

Front 15

noise-induced hearing loss

Back 15

Prolonged exposure
above 85 decibels can cause noise-induced hearing loss

Front 16

when adding amplitudes...

Back 16

you add the pressures, not the SPL! so adding two 80 dB saws=86 dB

Front 17

timbre

Back 17

the unique mixture of frequencies is a sound's timbre. simple vs. complex waveform

Front 18

loudness

Back 18

we are more sensitive to some frequencies than others, so loudness depends on amplitude and frequency.

Front 19

audibility curve

Back 19

this is a threshold for hearing as a function of frequency, and is not a horizontal line. we are more sensitive to some frequencies than others.

Front 20

audibility and threshold curves

Back 20

any point on any single curve is equal loudness, but they are not straight lines because loudness varies with frequency. the audibility curve shows the frequency to which we're most sensitive. the pain threshold flattens out, and above the threshold would be flat.

Front 21

the loud stereo problem

Back 21

if you turn the volume down, we are less sensitive to lowest and highest frequencies, so we hear a disporportionate amount of moderate frequencies. used to be buttons that would amplify low frequency sounds when the amplitude was low.