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Audiometry > Physics of Sound 1 > Flashcards

Physics of Sound 1 Flashcards

1
Q

Sound Definition

A

Propagation of density changes through an elastic medium through compression (higher conc) & rarefaction (lower conc)

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2
Q

Classes of Sounds

A
  • Pure Tones
  • Complex Periodic Noise
  • Continuous Noise
  • Transient Noise
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3
Q

Ingredients for Sound

A
  • Elastic Medium

- Vibrating Source

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4
Q

What kind of waves are sound waves?

A

Longitudinal Pressure Waves

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5
Q

Classes of Sound

A
  • Pure Tones (Sinosidal waves)
  • Complex Periodic Noise
  • Continuous Noise
  • Transient Noise
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6
Q

How does the air molecules in the sound medium move?

A

Air molecules oscillate about their equilibrium positions

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7
Q

Sound Features

A

Pitch: Frequency (Hz)
Loudness: Amplitude (Pressure Level- PA)

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8
Q

Period & Frequency Formulas

A 
Freq= 1/period
Period= 1/Freq
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9
Q

Pure Tone

A
  • Simple, naturally occurring wave pattern
  • Few natural sources
  • Periodic/ repeats regularly
  • Spectrum shows one frequency
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10
Q

Complex Waves

A
  • Few pure tones combined together with different amplitudes, frequencies and phases
  • Combination of pure tones may result in complex periodic noise or continuous noise
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11
Q

Complex Periodic Noise

A
  • Periodic
  • can be analyzed into component sine waves
  • spectrum shows frequency of component waves
  • all freqs are multiples of fundamental freq, f0, which is their HCF
  • made up of Fourier Series (series of sinusoids)
  • waveforms must satisfy a harmonic relationship, and belong to a harmonic series
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12
Q

Types of Complex Periodic Waves

A
  • Square Waves

- Sawtooth Waves

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13
Q

Square Waves

A

Odd integer multiple of f0 and identical starting phases

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14
Q

Sawtooth Waves

A

Odd and even components with identical starting phases

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15
Q

Continuous Noise

A
  • Not periodic
  • Many component frequencies/ not based on common fundamental frequency
  • Spectrum shows envelop rather than a line for all frequencies
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16
Q

Transient Noise

A
  • Not periodic
  • very short duration
  • all frequencies present
  • spectrum shown as an envelope
17
Q

Sound Intensity Definition

A
  • Sound energy passing through a unit area (etc. m^2) per unit time (etc. s)
  • unit for measuring the magnitude of vibration in the air
18
Q

Sound Intensity Unit

A

Watts per m^2 (W/m^2)

19
Q

Sound Intensity measurement

A

Relative measurement, known as relative intensity is preferred

20
Q

Sound Intensity Formula

A 
N (dB IL) = 10log10 Ix/Ir, 
where Ir=10^-12W/m^2 
Ix being relative, 
Ir being reference, 
IL being intensity level
21
Q

Sound Intensity Chart

A 
\+10dBIL= 10^x x 10
\+3dBIL = double of intensity (Ix)
-3dBIL = half of intensity (Ix)
22
Q

Sound Pressure

A

-force per unit area (N/m^2 or Pa)

23
Q

Sound Pressure Formula

A 
I = Prms^2/Po(S), 
where I=Intensity, 
Prms=rms pressure, 
Po=medium density, 
and S=speed of sound
24
Q

Air Pressure Standard Condition

A

Air as the medium,
I = 10^-12W/m^2,
creates a pressure of 20μPa

25
Q

Sound Pressure Level (SPL)

A

I = P^2/PoS,
dB SPL= 20log10(Px/Pr),
where Pr = 20μPa

26
Q

Sound Intensity and Loudness

A
  • Intensity =/ Loudness
  • Same intensity may not mean the same loudness
  • dependent on frequency
27
Q

Other dB Scales

A
  • Standard Contour Filter developed to cater to non-uniform hearing responses
  • denoted dBA, dBB and dBC, dB HL
28
Q

dBA Filter

A
  • commonly used to measure musical sound loudness

- most accurate approximation for medium hearing loss

29
Q

dBB & dBC filter

A
  • appropriate for monitoring loud sounds
  • hearing curve is flatter at very high sound intensity levels (from equal loudness curves)
  • dBC sometimes used for traffic noise surveys
30
Q

dB HL scale

A
  • references softest sound the average hearing can hear at a particular frequency
  • dB HL =/ 20μPa, and instead is frequency-dependent
  • etc. 40 dB HL means the person hears a pure tone 40dB above average

Audiometry (1 decks)

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