212- January 29th- Basics of Resonance

Resonance

A property of an object, specifically the response of an object to respond to frequencies that come close to it’s natural frequency, resulting in more amplitude.

Forced Vibration

the basis of resonance, how an object is forced to vibrate in response to vibrations of another object.

Driver

the object that supplies the driving/applied frequency

Resonator

The body that vibrates because of the driver

Resonant Frequency (RF)

The frequency at which the resonator undergoes the greatest vibratory response

Acoustic Resonance

Occurs when an air-filled container is forced to vibrate by applied frequencies.

Smaller volume = higher frequencies amplified

Larger volume = lower frequencies amplified

Tube Resonance

Dependant on length and whether ends are open or closed

Standing Waves

Produced when two identical waves travel in opposite directions, causing areas of negative and positive pressure to occur at the same time and same location

Nodes

points where waves interfere destructively and vibrate with minimal amplitude

Antinodes

points where waves interfere constructively and vibrate with maximal amplitude

Open Tube

Nodes form at midpoint, Antinodes form at ends

Halfwave resonator

Tube Closed at One End

Node will be somewhere, Antinode will be at opening

Quarter Wave Resonator

Acoustic Resonators as Filters

Amplify frequencies close to their RF

Bandwidth

Range of frequencies that a resonator responds to

Sharply Tuned

a regularly shaped resonator that responds to a narrow range of frequencies

Irregularly Shaped

like the vocal tract, these are broadly tuned and heavily damped.

Cutoff Frequencies

Frequencies at which the resonator no longer responds

Resonance Curve

Graph form to describe frequency response of a resonator

Resonant Frequency (F_c)

Center Frequency on a resonance curve

Upper Cutoff Frequency (F_u)

3 dB less intense response than the RF, upper limit

Lower Cutoff Frequency (F₁)

3 dB less intense response that the RF, lower limit

Bandwidth with Filters

Frequencies between upper and lower cutoffs

Attenuation Rate

the rate of decrease in amplitude, can be shallow, moderately steep, or extremely steep

Low-Pass Filter

Responds to acoustic energy below a certain F_u

High-Pass Filter

Responds to acoustic energy above a certain F_l

Band-Pass Filter

Passes energy in a range of frequencies (the bandwidth)

Band-Stop Fliter

Passes energy outside of the bandwidth