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Acoustics I: Basic Physics > Section 3 > Flashcards

Section 3 Flashcards

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1
Q

What are complex waves?

A

Characterized by a combination of different frequencies, amplitudes, and phase relationships. Can be periodic or aperiodic.

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2
Q

What does periodic mean?

A

Wave repeats over time and has a musical or tonal quality (musical notes, sustained vowels in speech)

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3
Q

What does aperiodic mean?

A

Wave does not repeat itself over time and has more of a “noise” type quality (transient sounds in speech and environment)

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4
Q

How do frequencies work in a periodic complex sound?

A

All frequencies are whole number multiples of the fundamental frequency (harmonic series)

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5
Q

What is the fundamental frequency?

A

the lowest frequency of vibration in a harmonic series

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6
Q

Explain harmonics

A

Any whole number multiple of the fundamental frequency

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7
Q

How does the fundamental frequency relate to the first harmonic?

A

They are the same number, since the fundamental frequency can be multiplied by itself.

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8
Q

How do you find the second harmonic?

A

The second harmonic is twice the fundamental, the third three times the fundamental, the fourth four times the fundamental, etc.

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9
Q

What is an overtone?

A

Any component in a complex tone having a frequency higher than the fundamental- the first overtone is equal to the second harmonic, etc.

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10
Q

What is a partial?

A

Indicates a part of partial of the complex tone or harmonic series- the fundamental frequency is also the first partial

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11
Q

What is an octave?

A

Any interval of two frequencies having a frequency ration of 2:1 (a doubling of the frequency)

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12
Q

Do harmonics all have equal amplitudes?

A

No, even though fundamental frequency determines all harmonic frequencies.

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13
Q

What is the result of two waves of different frequency and/or amplitude being generated simultaneously?

A

A new wave that is the sum of each of the separate waves.

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14
Q

What is a steady state sound?

A

Frequency, composition, amplitude and phase relationship of the partials of a tone are constant over time- usually periodic.

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15
Q

What is a transient sound?

A

A change in steady state- usually aperiodic.

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16
Q

What is a Fourier analysis? How is it represented? What is on this representation?

A

Shows that any complex sound can be broken down to show the individual sinusoidal components of that sound. Represented on a graph called a spectrum that shows the amplitude, frequency, and phase of each individual sine wave in a complex sound.

17
Q

What is an amplitude spectrum?

A

The ordinate will indicate the range of amplitudes, the abcissa will indicate the range of frequencies

18
Q

What is a phase spectrum?

A

Can also be plotted to show the starting phase of each individual sine wave

19
Q

What does each line on a spectrum represent?

A

An individual sine wave that is part of the complex sound (therefore the line will inherently represent the individual sine waves amplitude, frequency, and phase.

20
Q

What is interference?

A

The phenomenon that occurs when two waves meet while traveling along the same medium. The interference of waves causes the medium to take on a shape that results form the net effect of the two individual waves.

21
Q

What is constructive interference?

A

A type of interference where two interfering waves have a displacement in the same direction. Can occur where the two interfering waves are displaced upwards, or when they are displaced downward.

22
Q

What occurs when two interfering waves are in phase? (Started at the same phase and were identical in amplitude and frequency)

A

Would result in summation of the two waves and a doubling. Ex: If a sine wave with a max displacement of -1 interferes with a sine wave with the same frequency with a max displacement of -1 unit, the the resulting wave in the medium is a sine wave with a max displacement of -2 units.

23
Q

What is destructive interference?

A

Where two interfering waves have displacement in opposite directions. If a sine wave with a max displacement of +1 meets with a sine wave of -2, then the resulting displacement will be -1. If two interfering waves of the same frequency and amplitude meet but are 180 degrees out of phase, the waves will cancel each other out- resulting in no sound.

24
Q

Explain what a beat is

A

When two sound waves of almost identical frequency combine, the alternating constructive and destructive interference causes the sound to be alternatively soft and loud- sounding like it is “beating.”

25
Q

What is “noise”

A

Noise is a sound that has little or no periodicity- a sound with instantaneous amplitude that varies over time in a random manner.

26
Q

What is white noise?

A

All frequencies in a a specific range are present, regardless of phase, and the average power over a frequency range is constant. Average power is equal to the product of the frequency range and intensity.

27
Q

What is pink noise?

A

Amplitude decreases by one half with each doubling of frequency

28
Q

What is a low pass filter?

A

Attenuates high frequencies and passes low frequencies

29
Q

What is a high pass filter?

A

Attenuates low frequencies and passes high frequencies

30
Q

What is a combination filter?

A

A combination of a low and a high pass filter to pass a specific range of frequencies (narrow band or speech noise)

31
Q

What is a transient sound?

A

Speech, that is not steady, is a series of transient sounds. Transient sounds are aperiodic and change frequently.

32
Q

How did white noise get it’s name?

A

White noise gets it’s name from white light. All frequencies within a specific range are present regardless of the phase and all the intensities are the same. There will be single line at each frequency when looking at the spectrum.

33
Q

What is an ordinate on a spectrum?

A

Refers to an element plotted on the vertical axis and tells us the amplitude/intensity of sound

34
Q

What is an abcissa on a spectrum?

A

The horizontal axis of a spectrum, tells us the time.

35
Q

How common are pure tones? What are most sounds?

A

Not common in nature at all, usually complex sounds

Acoustics I: Basic Physics (4 decks)

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