Speech Science LEC 5

Lec 5, resonance, pgs 37-39

2 types of vibration

• free: the obj or medium vibrates freely after initial distrubrance

• forced: tendency of one medium to set another medium into vibration. the medium or obj is driven by an outside source that is itself an oscillator; need an outside source to continue vib

tacoma-narrows bridge/ natural(resonant) frequency

every object that vibrates(oscillates) has a certain frequency at which it vibrates at the widest amplitude most easily (which is why the bridge broke)

properties that determine the natural frequency

1) stiffness: more stiffness causes higher frequency

2) mass: more mass is less frequency (inverse)

3) length: more length is less frequency (inverse)

resonant frequency formula

resonant frequency= speed/wavelength

• speed + wavelength are dependent upon the properties of the medium

natural frequency

the greater the length the slower(lower) the frequency of vibration

ex: big church bell has a low frequency of vibration; small church bell has a higher frequency

resonance

1 object matches natural frequency(vib at same resonance) and sets/forces 2nd object into motion/vibration

• large increase in vibration when a force is applied at a natural frequency of the medium

source + resonator

• source: 1st obj vibrating

• resonator: obj or medium set into vibration

volume of containers influences resonance frequency

• larger volume, lower frequency

• smaller volume, higher frequency

2 types of resonators

• mechanic: objects (ex: tuning fork, pendulum, swing)

• acoustic: air in a completely or partially enclosed container (air highly elastic medium)

sharply tuned resonator

• the resonator responds to a small range of frequencies

• vibration persists for a long time (light damping)

• ex: a tunning fork, a crystal glass

broadly tuned resonator

• the resonator responds to a larger range of frequencies

• vibration dies out quickly (heaving damping)

• ex: sound in air, headphones, usually machines are broad tuned

acoustic system

source of energy (in the form of vibrations)

resonances that have their own natural frequency of the resonator

formants

natural frequencies that get intensified are called formants

acoustic resonance-amplification

energy’s vibration or source frequency matches the natural resonant frequency of the resonator, you get an AMPLIFICATION of the frequencies/greater intensity