Ch 5 (MIDTERM) Flashcards
causes sound to dissipate?
Impedance
Distance
Free Vibration
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
Forced Vibration
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
Driving Frequency
The wave that forces resonator into Vibration
Also called applied frequency
Resonator will usually vibrate if driving frequency has similar RF (resonating frequency)
Resonator
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
Filter/Resonator
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
Bandwidth
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)
Filters: Narrow bandwidth
Transmits small range of frequencies
usually symmetrical/regular shaped
allows less frequency but vibrates for longer (less dampening)
Filters: Broad Bandwidth
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
Cut-off frequency
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
Attenuation rate
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
Types of filters
Low pass filter
High pass filter
Bandpass filter
Band reject filter
Low pass filter
Transmits energy below a specific upper cut frequency (allows low to pass)
Frequency above upper cut-off attenuated
High pass filter
Transmits energy above specific lower cut-off frequency (allows high to pass)
frequency below lower cut-off attenuated
Bandpass filter
Transmits energy in range between lower and upper cut off
both lower and higher frequencies attenuated
Band Reject filter
Rejects all frequencies between the 2 cut offs
Idealized vs. realized
Ideally, resonator’s physical characteristics determine the resonance curve
reality, eardrum and oral cavity are resonators with malleable resonance
Impedance (Z)
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
Resistance (R)
Opposition of vibration caused by FRICTION
Same for all frequencies always
Energy lost due to particles interacting with each other
Reactance (X)
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)
As frequency increases…
Mass reactance INCREASES
Stiffness reactance DECREASES
As frequency decreases
Mass Reactance DECREASES
Stiffness Reactance INCREASES
Mass inhibits…
Higher frequencies
Stiffness inhibits…
Lower frequencies
Heavier objects are…
Better at lower frequencies where stiffness reactance dominations and mass reactance is lower
Harder to get heavier objects into faster vibration
Stiffer objects are…
Better at higher frequencies where mass reactance dominates and stiffness reactance is lower
Taut violin string vibrates faster easier
Mass and stiffness are…
180 degree out phase
Resonant frequency
Where mass and stiffness reactance cancel and meet resistance in the middle
Admittance (Y)
How easily system vibrates, reciprocal to impedance
Y=velocity/force
Sound dissipation from distance
Doubling distance from sound source spreads out energy pressure of sound
every double distance = 6dB DROP
Woofer speakers
Bigger speaker cones and heavier
transmits lower frequency well where it is stiffness dominated
Tweeter speakers
Lighter, transmits higher frequencies well where it is mass dominated
