self assessment one

Question 1

accurately describe the motion of a pendulum using the terms: displacement, velocity, and acceleration

Answer 1

Acceleration is at its max at the points of max displacement (where the pendulum momentarily stops before changing direction)
Velocity is at its greatest when the pendulum is passing through its equilibrium position (where acceleration is 0 because the velocity is constant)

(the function showing the change in the pendulum’s velocity has the same shape as the function for displacement, but it is shifted in time by a quarter of the time needed for the pendulum to complete 1 full back and forth movement)

Question 2

explain simple harmonic/sinusoidal motion and why it’s important in understanding waves

(from memory)

Answer 2

harmonic motion: acceleration of the object is directly proportional but opposite in direction to the displacement of the object from its equilibrium position
SHM: when any characteristic* of the shm is graphed as a function of time, it has the shape of a sine wave

*displacement, velocity, acceleration

Question 3

what are period and frequency?

Answer 3

frequency (f): number of cycles per second
period (T): the time requeired for the completion of one cycle of a waveform

(frequency and period are reciprocals)

cycle: one full repetition of a periodic motion
hertz: 1 cycle/second

Question 4

calculate the frequency of a waveform, given time and number of waveform cycles, or wavelength

Answer 4

frequency = cycles/sec

Question 5

calculate the period of a waveform, given the frequency, and vice versa

Answer 5

period= 1/frequency
frequency= 1/period

they are reciprocals

T=1/f
f=1/T

Question 6

determine the starting phase of a time waveform

Answer 6

starts at equilibrium, divide the wave into quarters, etc

Question 7

figure out how in or out of phase two waveforms are

Answer 7

find the distance between two congruent points

Question 8

determine the absolute amplitude of points along a waveform

Answer 8

just look at the graph?

Question 9

calculate the peak-to-peak amplitude of the condensations and rarefaction of a sinusoid

Answer 9

includes a compression and a rarefaction

Question 10

explain what the pendulum and mass & spring system have to do with sound

(from memory)

Answer 10

they have simple harmonic motion like a periodic wave

Question 11

use your understanding of Fourier theorem to discuss how a complex wave can be “put together” and “taken apart”

Answer 11

any complex oscillatory (vibratory) motion is the sum of various sinusoidal motions of varying amplitude, frequency, and phase

Question 12

determine whether a sound is (closer to) periodic or aperiodic by looking at either its time waveform or amplitude spectrum

Answer 12

amplitude spectrum goes down with harmonics for periodic
aperiodic: random everything

Question 13

calculate the fundamental period and frequency of a complex wave, as well as its harmonics

Answer 13

frequency=cycles/second
period=how long it takes for 1 cycle
harmonics are multiples of the fundamental

Question 14

accurately extract information from time, frequency , and phase domain graphs

Answer 14

i think i can do this

Question 15

teach someone what sound is from memory

Answer 15

sound is a disturbance in an elastic medium that propagates as a longitudinal wave (it can also be thought of as a stimulus that causes an auditory sensation, or an auditory sensation)
-it requires an energy source, vibrating object, and elastic medium

Question 16

discuss the relationship of density and stiffness to the speed of sound

(intelligently without notes)

Answer 16

• the greater the stiffness the faster the speed of sound (because the molecules are more interconnected)
• the lower the density the faster the speed of sound (because there is less mass to travel through)

Question 17

determine the wavelength of a waveform and use the waveform equation to find the missing variable: speed of sound, frequency, or wavelength

Answer 17

𝛌=C/freq

(wavelength=the speed of sound divided by the frequency-hz)

Question 18

intelligently discuss the difference between pressure and intensity and what they each measure

Answer 18

• sound pressure: the magnitude of change in local atmospheric pressure caused by the vibration of a sound source
• sound intensity: the amount of sound energy transferred to the surrounding medium in a certain period of time
  (ie. sound pressure is how compressed the molecules of a medium are at a particular place, and sound intensity is how much sound is flowing through a given point over time)

Question 19

use the inverse square law to understand the intensity/loudness of a sound, given its distance from a sound source

Answer 19

sound intensity is inversely proportional to the square of the distance from the sound source
ie. as you move away from the sound source (increasing the radius of the sound sphere) if you increase it by 1 it increases by 4 and by two by 9–think of the picture

intensity=power/4pi * r-squared (W/m-squared)

Question 20

enter a situation (room, stadium, auditorium, etc) and make educated inferences about the behavior of sound with your knowledge of absorption, reflection, reverbation, refraction, diffraction and other physical principles discussed in class

Question 21

calculate the various modes of vibration given the length of an open-closed tube

Answer 21

V/4L
odd number multiples

Question 22

talk about three important elements of the decibel and why they are important

intelligently

Answer 22

1. it allows for the numerical representation of physical magnitudes in a manner that correlates to human perception
2. it allows for the compression of a large range of physical values into a much smaller and more manageable range
3. it supports the metric system by using a base 10 logarithm

Question 23

estimate the dB SPL/HL for any sound given your knowledge of dB levels of common sounds

Answer 23

Common sources of painful and dangerous noises with a level between 120 and 140 dB include:
· aircraft taking off;
· thunderclap;
· jackhammer or chainsaw;
· gunshot from a high-caliber gun or firearm like a rifle or a shotgun.
Uncomfortable-
Common sources of 110-120 dB sound include:
· jet plane or helicopter;
· rock concert or symphony orchestra;
· large scale sporting events;
· car horn;
· leaf blower;
· power saw.
Very Loud
Common examples of 80-110 dB sounds include:
· playing music on your personal listening device or audio system at maximum volume - 100 dB;
· power tools – 90 dB;
· alarm clocks – 80 dB.
Irritating-
Here are some day-to-day sounds between 70 and 80 dB:
· garbage disposal or vacuum cleaner – 80 dB;
· car tires – 70 dB;
· average traffic noise – 70 dB.
Loud–Sounds ranging from 60 to 80 dB
The most common examples of sounds in this range are:
· busy restaurant – 70 to 80 dB;
· loud radio – 70 to 75 dB;
· city street – 70 dB;
· hairdryer – 70 dB;
· dishwasher – 70 dB;
· electric shaver – 60 dB;
· normal conversation – 60 dB.
Moderate noises are between 40 and 60 decibels.
· normal level of speech;
· rainfall;
· refrigerator;
· light traffic;
· a residential street.
Soft sounds, as the name suggests, are very mild and range from 20 to 40 dB.
Examples of soft sounds include:
· a quiet room;
· a person whispering;
· the sound of rustling leaves;
· a silent library.

Question 24

calculate the dB IL or dB SPL given its intensity or pressure

(using the reference from memory)

Answer 24

20log(p/20 uPa) -> [dB SPL]
10log(I/10^(-12)) -> [dB IL]

Question 25

explain why we need dB HL vs dB SPL

Answer 25

• dB HL is the level that is being heard by the listener
• 0 dB HL at a particular frequency corresponds to the dB SPL that is the RETSPL at that frequency

Question 26

explain what dB RETSPL is and why we need it

Answer 26

A RETSPL is the dB SPL that corresponds to threshold for a large group of normally hearing young adults
-threshold is the level at which a sound is barely perceptible
-we can figure out hearing level by comparing what a person hears to the RETSPL for that frequency

Question 27

convert the level of a sound from dB SPL to dB HL and vice versa

Answer 27

• dB HL = presentation level (dB SPL) – RETSPL
• dB SPL = dB HL + RETSPL

Question 28

convert the level of a sound from dB HL to dB SL and vice versa

Answer 28

• dB SL = presentation level (dB HL) – threshold (dB HL)
• Number of dB HL a particular sound is above/below a person’s threshold. (That individual’s threshold becomes the reference