Audiometry Flashcards

1
Q

How can the speed of sound waves be calculated?

A

product of wavelength and frequency

c = λ * f

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2
Q

What is acoustic impedance?

How is it calculated?

A

resistance type of quantity, characterizing the sound conducting medium
Z = c * ρ

  • c = velocity of sound in the medium
  • ρ = density of the medium
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3
Q

2 formulas to describe sound intensity.

A

average power of sound (P) incident perpendicular to a surface divided by the surface area (A)
J = P / A

or: square of the effective value of the pressure (peff) divided by the acoustic impedance (Z)
* *J = peff2 / Z**

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4
Q

What is the the coefficient of reflection?

Formula.

A

percentage of reflected intensity

R = Jrefl / J0 = ((Z1 - Z2) / (Z1 + Z2))2​

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5
Q

What is the characteristic frequency of the reference sound?

A

1000 Hz

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6
Q

What is the reference intensity?

A

intensity of the threshold of hearing at 1000 Hz (= reference sound)

J0 = 10-12 W/m2

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7
Q

What are Fourier analysis and harmonic synthesis?

A

Fourier analysis:

decomposition of a waveform (sound) into the series of harmonics of determined

  • frequencies
  • amplitudes
  • phase

Harmonic synthesis = reverse process of Fourier analysis

reconstruction of any periodic waveform from its harmonic components

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8
Q

Was is pitch?

How can you calculate it?

A

physiological sensation of the highness or lowness of the note
⇒ that is a logarithmic function of frequency (valid up to 1 kHz): noctave = log2 f2/f1

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9
Q

What is timbre?

A

determined by the amplitudes of the fundamental frequency and harmonics in the Fourier analysis of the waveform

  • pure sine wave
  • music
  • noise
  • transient
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10
Q

Give 2 formulas to calculate the intensity level.

A

logarithm of the intensity ratio
JdB = 10 lg (J1 / J2)

JdB = 10 lg (J / J0)

⇒ measured in dB

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11
Q

What is the loudness level?

It was introduced by.. ?

In which unit is it measured?

By how much do we have to increase it in order to achieve a 2 times louder sound senation

A

sound of different frequency appears at same loudness level at different intensities (cf. blue curves)
introduced by Weber-Fechner

Lphon = JdB 1000 Hz = 10 lg (J / J0)1000 Hz

Phon value of any frequency = dB value of the reference sound (1000 Hz, sin)

  • ex: 90 phon = 90 dB at 1000 Hz
  • BUT: +10 phon = +10 dB (at 1000 Hz) = 2 times louder sound sensation
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12
Q

What is the loudness?

In which unit is it measured?

1 [unit] refers to which intensity level?

What is the formula to convert it to dB?

By how much do we have to increase it in order to achieve a 2 times louder sound senation

A

psychophysical quantity, its value represents how loud we feel a sound of given intensity
→ derivation of Steven’s law:

Lson = 1/16 (J / J0)0.3

  • 1 sone = 40 phon
  • BUT: +1 sone = +10 phon = 2 times louder sound sensation
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13
Q

What is the threshold of hearing?

A

smallest intensity of sound at a given frequency that human ear can just hear (approx. 10-12 W/m2)

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14
Q

What is the threshold for pain?

Intensity?

A

highest intensity of sound that one can tolerate for a short time without any harm (approx. 10 W/m<strong>2</strong>)

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15
Q

What do the blue lines on the equal loudness curve plot resemble?

Conclusions?

A

equal loudness curves = isophon curves ⇒ same sensed loudness at different frequencies

conclusions:

  • the lower the sound (frequency), the higher the intensity (dB) to hear a sound of the same loudness
  • threshold of hearing = 0 phon
  • threshold of pain = 130 phon
    • 10 phon = + 10 dB (at 1000 Hz)
      + 1 sone = + 10 phon
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16
Q

Which quantities are brought into relation in Steven’s law?

Formula.

A

relationship btw the stimulus and sensation (valid for every sensory process)

S = const (J / J0)n

  • S = power of sensation
  • n = exponent corresponding to part. sens. proc.
17
Q

Relate Steven’s and Weber-Fechner’s law in a graph.

A
18
Q

What is the minimum time for a sound stimulus?

A

0.2 s, for tests at least 1.0 s

19
Q

What is responsible for additional hearing loss?

How is it measured?

When do we speak of impaired hearing?

A

over a certain loudness level the impairment is proportional to the received dose of the sound ⇒ causes hearing loss
D = J * t

  • D = dose
  • J = intensity
  • t = time

→ impaired if hearing loss of - 30 dB

20
Q

How is audiometry done?

A
  1. Recording the threshold of hearing as a function of frequency
  2. compared to the normal value of the threshold of hearing at given frequency → difference in [dB] = hearing loss
  3. audiogram can be constructed
21
Q

What is an audiogram?

Draw it.

A

hearing loss (dB) vs. frequency plot

22
Q

What is a pure-tone audiometer?

Differentiate.

What is it used for?

A

device that generates output of harmonic (sinusoidal) voltage of adjustable frequencies to air/bone conduction headphones

  • air conduction: normal headphones, entire ear tested
  • bone conduction: bone vibrator attached to mastoid bone, middle ear does not participate → less sensitive by 40 - 60 dB

⇒ difference btw 2 audiograms indicates injuries of middle ear

23
Q

How is normal hearing loss called?

At what age does it usually start?

A

presbyscusia = usually - 3dB

starts at 20

24
Q
A

NOCH AUSSTEHEND!