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AUDI 514 - Hearing Science > Lecture 2 > Flashcards

Lecture 2 Flashcards

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1
Q

What is pressure?

A

Force/unit area. Units are pascals.
For a given area, larger pressure means larger force is being applied.
Weight of air above us causes an atmospheric pressure to envelope us.

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2
Q

What is pressure like in the atmosphere?

A

Column of air pushing pressure air molecules, being pulled down by gravity. Higher pressure near earth’s surface compared to the atmosphere.

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3
Q

What is sound pressure?

A

Depends on weather systems. Zones create our weather.
Always have positive pressure values. Speech sounds are positive/negative relative to our atmospheric pressure. (Sinusoid wave and pressure over time) = same relation

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4
Q

How do you measure the magnitude of sounds?

A

Amount of movement or displacement - dB value, pressure value - movement of molecules of air
Amounts of energy that is spent
Pressure that results from the motion. Ears respond to production of pressure
How many moles of atoms in a particular volume changes speed of sounds in a medium

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5
Q

What is the formula for sound intensity?

A

I = p2/(ρ0c)
p0 - density of medium
c - speed of sound

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6
Q

How is the perception of intensity measured?

A

As a unit of pressure (dB).
Sound pressure - dB SPL
Softest we can hear is 20 micropascals (Minimal audible threshold)

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7
Q

Intensity and Decibels: what is the formula for the ratio of two intensities?
Intensity

A

dB = 10log(Ix/Io)
Ix - absolute intensity of the wave in question
Io - absolute intensity of a reference sound (10^-12)
UNITS = dBIL

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8
Q

What is the formula for sound pressure level?

Pressure

A

Lspl = 20logp/po
po - standard pressure reference of 20 micropascals
UNITS = dBSPL

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9
Q

What happens when you reduced sound pressure by one half?

A

Reduces the decibel level by 6dB

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10
Q

What is the relationship between sound power (intensity) and sound pressure (dB)?

A

Power = Intensity
Power = p^2
Intensity (proportional to) p^2

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11
Q

What are the two standard references?

A

dB IL - intensity level (10^-12 watts/m^2)
dB SPL - sound pressure level (2x10^-5 Newtons/m^2)
60dB SPL = 60dB IL

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12
Q

Does intensity equal loudness?

A

NO.

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13
Q

Sound Propagation: How is transmission of sound made possible?

A

Because the energy changes about the static atmospheric air pressure (the medium)
Molecule pushed around as the object vibrates - have resistance due to friction = heat. (Friction drops intensity)

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14
Q

In sound propagation, what is the condensation and rarefaction phase?

A

Condensation: molecules squeezed together
Rarefaction: density of molecules decreases
Higher density = higher pressure (vice versa)

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15
Q

What is the difference between a longitudinal and transverse wave?

A

Longitudinal - over a distance, like mass-spring motion. Sound consists of longitudinal pressure variations in a medium

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16
Q

In sound propagation, what is the speed of sound?

When is sound in air faster?

A

c = 345m/s

Sound in air is faster when temperature is increased, density is decreased and humidity is increased.

17
Q

What is the formula for wavelength?

A

λ = c T
c = 345m/s
T = seconds/cycle
λ = cm

Period in time related to frequency
Wavelength in distance value

18
Q

How does a sinusoid describe the pressure distribution at a given plane in a pipe as time passes?

A

Condensations and rarefactions propagate past the plane in the pipe. Sound pressure across time - frequency (Hz)
Amplitude can be across time and distance
Wavelengths in tubes - like the trachea (not in reality)

19
Q

What is the inverse square law?

A

As the radius increases, the pressure drops as the inverse square of the distance
Analogous to a constant force being exerted on a larger area - pressure (F/A) decreases

20
Q

What does intensity have to do with the inverse square law?

A

Intensity varies inversely with the square of the distance.
Power drops by the sqaure of the radius
For sound - force stays constant, area expands.

21
Q

Sound intensity - effect of distance: What is the relationship?

A

Intensity is proportional to 1/r^2
Intensity is inversely proportional to distance from the sound source.
If distance doubled, sound intensity decreases by a factor of 4.

22
Q

What is the relationship between pressure and distance?

A

Since pressure is proportional to the square root of intensity, pressure is proportional to the radius.
pressure is proportional to 1/r
If distance doubled, sound pressure decreases by a factor of 2

23
Q

What is the relationship between the level (dB) and the distance from the sound source?
How does this apply to children with HL?

A

Doubling the radius will 1/4 the intensity, and 1/2 the pressure.
Reducing the peak pressure by half = reducing RMS pressure by half for sinusoids.

HL Child: FM devices remove distance - transmits directly into a person’s ear. Child should sit at the front of the class where dB level is highest.

24
Q

What happens when you double the distance?

A

Results in a 6 dB decrease in pressure and intensity.

25
Q

What is impedance?

A

Obstacles that impede the propagation of the sound wave. If impedance is large, motion is hindered.
Mass reactance increases with increasing frequencies.
Stiffness reactance increases with decreasing frequency.

26
Q

What is characteristic impedance (and reflections)?

What is impedance mismatch?

A

Any medium has its own characteristic impedance - sound intensity varies according to the impedance of the medium (can absorb, transmit or reflect it)
If a sound wave encounters a change in media, a portion of the sound wave will be reflected from the surface with greater characteristic impedance. This reflection appears as a reflected sound wave.
The greater the impedance mismatch, the greater the reflection.

27
Q

What occurs with sounds waves reflecting off a hard and acoustically “smooth” boundary?

A

Waves radiate in all directions from sound source, reflected waves propagate as if they originated from sound image located some distance behind boundary as the sound source is in front of it.

28
Q

What is the difference between reflection and impedance?

A

Reflection at an object can cause echoes.
Impedance measures how much a material resists being moved.
Sound waves will be reflected by materials with a higher impedance than air (bounce off)

29
Q

What is interference?
What is destructive vs. constructive interference?
(Of reflected waves)

A

Constructively - net wave amplitude is larger
Destructively - net wave amplitude is smaller
When waveforms of either same or differing phases are combined, they interfere with each other and their instantaneous amplitudes are summers to create a new composite wave.

30
Q

How is it possible for constructive and destructive interference at the same time?

A

Mixture or sine and cosine wave of equal amplitude and frequency. Result is a sinus-shaped wave of slightly greater amplitude than either component, but slightly out of phase with both.

31
Q

How do standing waves work?

A

Will only occur at resonant frequencies.
Sum of forward and reflected wave created has peak amplitude varying with position. Some points have high peak pressure (antinodes), and some have zero peak pressure (nodes)
Can be in the ear canal, vocal tract**

32
Q

What is reverberation?

What is reverberation time?

A

In a room, reflections occurs off all surfaces. Reflections also reflect off other surfaces.
Reverberation time - time taken for a reverberant sound to die off to level 60dB below its original pressure.
More reflective room = longer time for sound to die away.
Larger rooms have longer reverberation times.

33
Q

What is sound transmission?

A

Acoustic energy is passed through the object and its neighbours.

34
Q

What is sound absorption?

A

Absorption - acoustic energy converted to heat.
Characteristics depend on resonant properties of object. Time that is takes to get to the medium and reflected.
Most materials are generally better at absorbing high frequencies vs. low.

35
Q

What is diffraction?

Why is it important for hearing?

A

Bending of waves around obstacles.
Low frequency sounds diffract more than high frequency sounds (can hear sounds better around obstacles)
Important for hearing because if a low frequency component is coming from the right it will diffract around the head to reach the left ear - heard in both ears.
Around your head, frequency will determine how wide the shadow is. Smaller head = less sound shadow for that frequency.

36
Q

What are sound shadows in diffraction?

A

Objects with dimensions equal to or larger than the sound wavelength will have a shadow. Area where frequency of interest has smaller amplitude - depends on wavelength.
Shadow created in certain frequency.
λ = c / f

37
Q

Standing Wave on Strings:

How is fundamental frequency related?

A

The lowest frequency called the fundamental frequency or the 1st harmonic = v/2L
Higher frequencies are called harmonics (2nd = f=v/L)
Integer multiples of 1st harmonic are labelled as 3rd (f = 3v/2L)

AUDI 514 - Hearing Science (15 decks)

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