HW 1: Sound, Acoustics, Psychoacoustic

Sound waves propagating through the air are longitudinal

true

Decibels are used to represent power ratios on a logarithmic scale

true

the speed of sound through air at a temperature 20C is approximately ____ meters per second
A) 120

B) 10¹²

C) 332

D) 20,000

E) 440

F) 343

F

___ vibration occurs when the energy from a vibrating object is transferred to another object, causing the second object to exhibit a similar movement pattern

sympathetic vibration

Loudness is an objective, acoustical property of sound.

false

The wavelength of a 4 kHz sine wave under normal conditions (air propagation, 20°C) is approximately _________.

A) 1373200 meters

B) 1373.2 meters

C) cannot be determined from given information

D) 0.086 meters

E) 85.75 meters

D

When a rarefaction from one wave meets a rarefaction from a second wave at the same point in space, _____________ interference occurs.

A) resonant

B) constructive

C) destructive

D) periodic

E) logarithmic

B

________________ is a term that may refer to a non-periodic wave, or sound in an audio recording situation which is considered undesirable.

noise

The period of a 40 Hz wave is exactly ____________ seconds.

0.025

What is the frequency, in kHz, of a sound wave whose wavelength is 137.2 millimeters? Assume the speed of sound is 343 meters per second (be mindful of unit conversions).  __________ kHz

2.5

A(n) ________________ is formed by two periodic vibrations whose frequencies have a ratio of 2:1.

octave

Piano strings are stimulated by a lateral hammer strike. A propagating wave created by this type of excitation is a ______________ wave.

A) longitudinal

B) transverse

B

The audible spectrum spans approximately _____ consecutive octaves.

A) 100

B) 1,000

C) 20,000

D) 50

E) 10

E

Choose the response which most accurately summarizes the Fourier Theorem.

A) Two waves can pass through one another in the same physical space while retaining their original characteristics.

B) Frequency and period are inversely related.

C) Any periodic waveform can be expressed as a sum of sinusoidal vibrations.

D) Loudness can be expressed as a function of frequency and intensity.

E) The speed of sound is equal to the product of frequency and wavelengt

C

100 kHz is classifiable as a(n) _______________ frequency.

A) ultrasonic

B) infrasonic

C) audible

D) spectromorphic

E) subsonic

A

fundamental only

sine wave

odd-numbered harmonics only, amplitude of each partial = 1/n

square wave

odd-numbered harmonics only, amplitude of each partial = 1/n²

triangle wave

all harmonics, amplitude of each partial = 1/n

sawtooth wave

A segment of an amplitude envelope in which the amplitude is changing is called a(n) ________________ stage.

transient

Sound intensity is a measure of ________ distributed over ________.

power, area

A quadrupling of sound power corresponds to a ____ dB increase.

A) 2

B) 6

C) 4

D) 12

E) 3

B

Two similar but uncorrelated sounds, each with a sound pressure level of 40 dB, will sum to create an 80 dB SPL sound.

false

A tenfold increase in sound power (e.g. 100 Watts to 1,000 Watts) is equal to an increase of 1 bel.

true

_____________ is the phenomenon in which wave propagation speed changes as a result of entering a different medium, often with a different temperature. This causes the wave trajectory to behave as if it is "bending" as it enters this new medium.

A) interference

B) refraction

C) reflection

D) absorption

E) diffraction

B

Musical intervals consisting of irreducible, higher value ratios (e.g. 64:45) are generally considered to be more consonant than smaller, simpler interval ratios (e.g. 3:2), which are considered to be more dissonant.

false

Two sine waves at 50 Hz have a zero radian phase difference. The highest pressure region of one sine wave measures 0.001 Pa. When these waves are summed, the highest pressure region of the sum waveform is 0.01 Pa. What is the highest pressure of the second sine wave?

A) 0.009 Pa

B) 0.01

C) .001

D) 0.09

A

________________ is a field of study concerned with the relationship between physical auditory stimuli and the subjective, perceptual responses they elicit in the human brain/ear.

psychoacoustic

What is the most reasonable approximation for the sound pressure level in a normal school classroom during a lecture?

A) 0 dB SPL

B) -100 dB SPL

C) 50 dB SPL

D) 100 dB SPL

E) -50 dB SPL

C

What do Fletcher and Munson’s equal loudness contours tell us about the relative sensitivity of the ear to various ranges along the audible spectrum? Select all that apply.

A) The ear experiences a decrease in sensitivity between 2 kHz and 5 kHz.

B) The ear experiences a decrease in sensitivity below 200 Hz.

C) The ear experiences an increase in sensitivity below 200 Hz.

D) Sound pressure level is unrelated to perceived loudness.

E) The ear is equally sensitive to all frequencies.

F) All frequencies above 10 kHz sound equally loud.

G) The ear experiences an increase in sensitivity between 2 kHz and 5 kHz.

B, G

A ____________ wave occurs when a periodic vibration bounces back and forth between parallel surfaces.

standing

Low frequencies generally exhibit less diffraction than high frequencies.

false

The 6th harmonic of a 250 Hz fundamental has a frequency of exactly _________ Hz.

1500

Consider a 300 Hz fundamental. Is 2 kHz a harmonic or inharmonic partial?

A) harmonic

B) inharmonic

C) neither

B

The time domain is used to depict the amplitude of a sound wave as a function of time, and the frequency domain is used to depict the amplitude of a sound wave as a function of frequency.

true

When used to measure environmental sound pressure level, 0 decibels represents the threshold of pain, and -120 decibels represents the threshold of hearing.

false

One sine wave at 400 Hz and a second sine wave at 402 Hz are superimposed in a linear system, producing periodic amplitude fluctuations. The most common name for this auditory/perceptual phenomenon is ______________

beating

The ability of sound to travel around the corners of buildings, through small openings, and otherwise navigate around obstacles is a result of a process called _______________.

diffraction

A 200 Hz sound wave is propagating through air with a temperature of 27°C. What is its wavelength, in meters? Use the formulas presented in lecture.

1.7375