Ch 5 (MIDTERM)

Question 1

causes sound to dissipate?

Answer 1

Impedance
Distance

Question 2

Free Vibration

Answer 2

Object vibrates freely without interference at a rate determined by its physical characteristics such as mass, tension, and sitffness

Once set in motion, it will always vibrate at its own frequency (natural resonance/Resonant frequency)
i.e. eardrums, vocal folds

Question 3

Forced Vibration

Answer 3

Vibration from one object can set another object into vibration if the resonant frequency of both objects are reasonably close
i.e. opera singer and glass

Question 4

Driving Frequency

Answer 4

The wave that forces resonator into Vibration
Also called applied frequency

Resonator will usually vibrate if driving frequency has similar RF (resonating frequency)

Question 5

Resonator

Answer 5

Something set into vibration by another vibration
Does not initiate sound, closer the RF of the driving frequency to resonator, greater the response or amplitude

Question 6

Filter/Resonator

Answer 6

A medium where sound goes through (i.e. talking through a tube)

Anything that resonates is a filter, and a resonator’s characteristics determine what frequencies are allowed to be transmitted

If it falls out of the filter’s range, sound won’t be transmitted

Question 7

Bandwidth

Answer 7

Range of frequencies that it will transmit with minimal attenuation

if frequency falls out of bandwidth, then there will still be sound, but less amplitude (attenuated)

Question 8

Filters: Narrow bandwidth

Answer 8

Transmits small range of frequencies
usually symmetrical/regular shaped
allows less frequency but vibrates for longer (less dampening)

Question 9

Filters: Broad Bandwidth

Answer 9

Transmits larger range of frequencies
Asymmetrical/irregularly shaped
Allows more frequencies but vibrates for shorter (heavy dampening)

more common in speech and hearing with eardrum, VF, and microphones

Question 10

Cut-off frequency

Answer 10

Bandwidth’s maximum and minimum
can be determined by taking half of the bandwidth and going up and down 1/2 the resonant frequency

each cut off is 3dB down point from maximum and a 1/2 reduction of amplitude

Question 11

Attenuation rate

Answer 11

Roll off rate/slope
rate of which resonators amplitude decreases, how rapidly it decreases
dB/octave unit
usually occurs from point of cut-offs

Shallow roll-off: less than 18dB/octave
Moderate roll off: between 18-48dB/octave
Steep roll off: more than 90dB/octave

Question 12

Types of filters

Answer 12

Low pass filter
High pass filter
Bandpass filter
Band reject filter

Question 13

Low pass filter

Answer 13

Transmits energy below a specific upper cut frequency (allows low to pass)
Frequency above upper cut-off attenuated

Question 14

High pass filter

Answer 14

Transmits energy above specific lower cut-off frequency (allows high to pass)
frequency below lower cut-off attenuated

Question 15

Bandpass filter

Answer 15

Transmits energy in range between lower and upper cut off
both lower and higher frequencies attenuated

Question 16

Band Reject filter

Answer 16

Rejects all frequencies between the 2 cut offs

Question 17

Idealized vs. realized

Answer 17

Ideally, resonator’s physical characteristics determine the resonance curve
reality, eardrum and oral cavity are resonators with malleable resonance

Question 18

Impedance (Z)

Answer 18

Opposition to flow of energy/vibration
Measure of how difficult it is to set particles of medium into motion
Z=force/velocity
Composed of 2 types: Resistance and Reactance

Question 19

Resistance (R)

Answer 19

Opposition of vibration caused by FRICTION
Same for all frequencies always
Energy lost due to particles interacting with each other

Question 20

Reactance (X)

Answer 20

Opposition produced by the mass (density) and elasticity (stiffness) of medium
Varies as function of frequency
Composed of two types:
-Mass Reactance (Xm)
-Stiffness Reactance (Xs)

Question 21

As frequency increases…

Answer 21

Mass reactance INCREASES
Stiffness reactance DECREASES

Question 22

As frequency decreases

Answer 22

Mass Reactance DECREASES
Stiffness Reactance INCREASES

Question 23

Mass inhibits…

Answer 23

Higher frequencies

Question 24

Stiffness inhibits…

Answer 24

Lower frequencies

Question 25

Heavier objects are…

Answer 25

Better at lower frequencies where stiffness reactance dominations and mass reactance is lower

Harder to get heavier objects into faster vibration

Question 26

Stiffer objects are…

Answer 26

Better at higher frequencies where mass reactance dominates and stiffness reactance is lower

Taut violin string vibrates faster easier

Question 27

Mass and stiffness are…

Answer 27

180 degree out phase

Question 28

Resonant frequency

Answer 28

Where mass and stiffness reactance cancel and meet resistance in the middle

Question 29

Admittance (Y)

Answer 29

How easily system vibrates, reciprocal to impedance
Y=velocity/force

Question 30

Sound dissipation from distance

Answer 30

Doubling distance from sound source spreads out energy pressure of sound
every double distance = 6dB DROP

Question 31

Woofer speakers

Answer 31

Bigger speaker cones and heavier
transmits lower frequency well where it is stiffness dominated

Question 32

Tweeter speakers

Answer 32

Lighter, transmits higher frequencies well where it is mass dominated