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CHAPTER 2

CHAPTER 2. SINUSOIDS: THE BASIC SOUND. Hearing Science-- what is it?. The study of the normal process of hearing. Acoustics--the nature of sound Anatomy & Physiology of the Ear Psychoacoustics. Defining SOUND.

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CHAPTER 2

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  1. CHAPTER 2 SINUSOIDS: THE BASIC SOUND

  2. Hearing Science-- what is it? • The study of the normal process of hearing. Acoustics--the nature of sound Anatomy & Physiology of the Ear Psychoacoustics

  3. Defining SOUND • Psychological definition: Sound is a stimulus with the capability of producing an audible sensation. • Physical definition: Energy produced by an object in vibration and transmitted through a medium.

  4. VIBRATION • vibration is the movement of an object from one point in space to another, and usually back to the first point. • Objects that can be set into vibration have two properties: • elasticity • inertia (fundamental feature of mass)

  5. Elasticity is: • The property that allows an object or substance to return to its initial shape or state when it is deformed, distorted or displaced. • Tuning fork: stiffness provides restoring force • Swing: gravity provides restoring force

  6. Quantities Come in 2 Flavors: • Scalar Quantities • magnitude only • Vectorial or Vector Quantities • magnitude AND direction

  7. Scalar Quantities • Have magnitude only • Examples include Mass, Length, Volume • Can be added or subtracted directly

  8. Vector Quantities • Have BOTH magnitude and direction • Example: Velocity • Combining Vectors is more complicated

  9. Basic Units • Length • Time • Mass • (Charge)

  10. Other Units may be derived: • Area = Length x Length (or L2) • Volume = L3 • Speed = Length/Time • Acceleration = L/T2

  11. Force: A push or a pull • Force = Acceleration x mass • Therefore Force = ML/T2 • MKS force unit is Newton = 1 kg m/s2 • cgs unit is dyne = 1 g cm/s2

  12. Force and Elasticity • Hooke’s Law: • Force = (-)spring constant times displacement • Stress = force per unit area (aka pressure) • Strain = change in length • Stress = Elasticity x Strain

  13. Friction • Energy converted into heat when molecules rub against each other. • To move an object, the applied force must overcome friction. • Effect of Friction is “Resistance”

  14. Friction produces Resistance • Resistance = ratio of Force to resulting velocity (R = f/v) • measured in Ohms • Acoustically, we talk about the influence of friction as DAMPING

  15. Energy & Related Concepts • WORK • POTENTIAL AND KINETIC ENERGY • POWER

  16. WORK • Force applied through a distance • No motion--no work • Work = force x distance = ML/T2 x L • Units JOULE = 1 Newton Meter • erg = 1 dyne cm

  17. ENERGY COMES IN 2 FLAVORS • Kinetic-- Energy of motion • (Inertia can be thought of as the ability to store kinetic energy) • Potential--Energy of position • (Elasticity --ability to store potential energy)

  18. POWER • Rate at which work is done • Work/Time • Unit Watt = joule/second or 107 erg/sec

  19. SIMPLE HARMONIC MOTION • Vibration involves interplay of force, inertia, elasticity, and friction • Applying a force displaces object • Overcoming inertia • Traveling away from rest until ?

  20. Simple Harmonic Motion 2 • Why does object stop and then move back toward rest? • Why doesn’t the object then stop at rest? • Where is potential energy the greatest? • Where is kinetic energy the greatest?

  21. SHM 3 • Why does displacement decrease over time? • RESISTANCE • -- Energy is lost to HEAT through FRICTION

  22. SHM 4 • Amplitude --Displacement • Period-- Time taken to complete one cycle • Frequency--Number of Cycles per Second • Phase--Describing points in the Cycle

  23. A Waveform Shows Amplitude as a Function of Time PEAK PEAK-TO-PEAK

  24. Period and Frequency • Frequency = 1/Period (in seconds) • Units of Frequency = cycles per second or HERTZ

  25. PHASE--Each cycle broken up into 360 degrees • 0 degrees = 0 displacement and about to head positively • 90 degrees = positive maximum • 180 degrees=0 disp. About to head negatively • 270 degrees= negative maximum

  26. Phase Values Through a Cycle 90 180 270 360

  27. AMPLITUDE MEASURES • Instantaneous- amplitude at any given instant • Peak • Peak to Peak • Root Mean Square--A way of getting average amplitude • =Square root of Averaged Squared Amplitudes

  28. FREE VIBRATION • Pendulum illustration represents FREE VIBRATION • Force applied and object allowed to respond • Frequency of Free Vibration =Resonant or NaturalFreq. • --determined by the object’s Mass and Stiffness

  29. FORCED VIBRATION • Force is applied back and forth • Vibration occurs at the frequency of the applied force • Object’s mass and stiffness determine amplitude of vibration

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