Sound and its measurements

What is acoustics?

The study of the physical properties of sound in the environment

What is the perceptual characteristic of intensity called?

Loudness

What is the perceptual characteristic of frequency called?

Pitch

What is the perceptual characteristic of energy called?

Quality/timbre

What is the physical characteristic of loudness called?

Intensity

What is the physical characteristic of pitch called?

Frequency

What is the physical characteristic of quality/timbre called?

energy

What is sound?

Vibrations that are carried through the air in the form of pressure waves

What are the requirements for sound?

Source and a medium

What is a source of sound?

An object or event that produces vibration

What are some examples of a source of sound?

Vocal folds, tuning fork, etc.

What is a medium of sound?

The matter that the sound has to travel through

What are examples of a medium of sound?

Air, water, solids

What is the compression of sound waves?

A region of increased pressure where particles of the medium are squeezed together, creating a higher density

What is the rarefaction of sound waves?

A region in a sound wave where the particles of the medium are spread apart, resulting in a temporary decrease in pressure and density

What is a cycle/period?

One full wave, or 360 degrees

Where does a sine wave start?

0 degrees

Where does a cosine wave start?

90 degrees

What is frequency?

number of vibrations or oscillations occurring during a set period of time

What are Hertz?

the number of cycles/periods per second

What is the unit of frequency?

Hertz

What is period?

Time in seconds required to complete one cycle

What is the equation for period?

T = 1/f

What is the equation for frequency, looking at period?

f = 1/T

What is the one thing to remember when calculating period and frequency?

Time has to be in seconds!

What is sound velocity?

Speed of sound from the source to another point within the medium

Does sound move faster through solids, liquids, or gases?

Solids

What is velocity measured in?

meters per second

What is wavelength?

The distance for one cycle

What is the equation for wavelength?

λ= v/f

What is the speed of sound in air?

344 m/s

What is the speed of sound in water?

1433 m/s

What is the difference between wavelength and period?

Wavelength looks at the distance needed for one cycle, while period looks at the time it takes.

What is the equation for frequency, looking at velocity and wavelength?

f = c/λ

What are beats?

The noticeable increase and decrease in sound intensity when two tones of almost identical frequency are presented slightly "out of phase"

What are complex waves?

Sum of individual pure tone components

What are examples of complex waves?

Vocalizations of speech sounds

What are oscilloscopes?

A tool that measures and analyzes sounds

What is Fourier analysis?

The breakdown of a complex wave into its simplest (sinusoidal) components

What are harmonics?

Frequencies that are positive integer multiples of a fundamental frequency

What are speech formants?

A peak in the output frequency spectrum resulting from altering the shape of the vocal tract

What is amplitude?

The extent of the vibratory movement of a mass from its position of rest to the point farthest from the position of rest

What axis is amplitude on?

y-axis

What is amplitude affected by?

Force

What is force?

The impetus required to institute or alter the velocity of a mass

What is intensity?

Amount of force per unit of area

What is the inverse square law?

Intensity decreases proportionately to the square of the distance from the sound source

What is the equation for the inverse square law?

i1/i2 = [(d2)^2]/[(d1)^2]

What is a decibel?

The unit for intensity that expresses the ratio between two sound pressures or powers

What is the unit of intensity?

Decibel

What decibel system captures the auditory system of humans?

dB A

What does dB A emphasize?

Middle range sounds, just like our auditory system

What does dB B emphasize?

Moderately loud sounds

What does dB C emphasize?

Loud and impulsive sounds, such as heavy machinery

What does 1 dB equal in terms of a Bel?

1/10 of a Bel

What are 3 important characteristics of the decibel scale?

It's the ratio between two numbers, a logarithmic scale, and decibel levels can be specified with various references

What is the equation for dB intensity level?

dB (IL) = 10 x log (Io/Ir)

What does iR equal?

10^-12 watt/meter^2

True or false: Intensity is proportional to the square of sound pressure

True

What is the equation for dB sound-pressure level?

dB (SPL) = 20 x log(Po/Pr)

What is the sound-pressure level reference?

20 µPa = 0 dB SPL

What is the rule for dB IL when doubling dB?

Add 3 to the original value

What is the rule for dB SPL when doubling dB?

Add 6 to the original value

What is the threshold of audibility?

Human hearing sensitivity

What sounds are humans most sensitive to?

1k-4k

What type of dB scale do audiometers use?

dB HL

What is on the y-axis of an audiogram?

Hearing level in dB

How are dB HL and dB SPL graphs related?

The threshold of hearing calculated on the dB SPL graph is equated to 0 dB on the dB HL graph