Speech & Hearing Sciences Notes PDF

Speech & Hearing Sciences Notes Closed book quiz Ch Intro & History ignore but EBP must know Ch 1- 2 onwards below - **Sound** has no weight, substance, or mass - Sound is a set of movements, vibrations, disturbances, perturbations; - Sound does not itself travel, but is continuously...

Speech & Hearing Sciences Notes Closed book quiz Ch Intro & History ignore but EBP must know Ch 1- 2 onwards below - **Sound** has no weight, substance, or mass - Sound is a set of movements, vibrations, disturbances, perturbations; - Sound does not itself travel, but is continuously transferred - Sound is invisible\ Sound is (almost always) very complex - Sound is the propagation of a pressure wave in space and time through a medium **[Sound system]** - **Source**-anything that vibrates - **Medium**-anything with molecules - What about sounds in a vacuum such as space? - **Receiver**-anything that can detect vibrations **[Metaphysics of sound]** - An important aspect of sound is **detection** of vibration of a source that's passed through\ a medium. For people, brains are important detectors. - **ACOUSTICS:** branch of physics dealing with the generation, transmission, and modification of sound waves **[Speed of sound]**\ **Propagation velocity** depends on the properties of the medium **Elasticity:** rigidity, deformation characteristics;\ absorption of energy; higher elasticity results in faster speed **Hooke\'s Law:** stress is negatively proportional to strain; or, stress ∝ −strain\ Young\'s modulus is the ratio of stress to strain, rendered in gigapascals (GPa) for us\ Ex., compare steel (200 GPa) and rubber (.01 GPa); human tendon (7 GPa) and bone (14 GPa) **Density:** mass of substance per volume; higher density results in faster speed\ Ex., hyrodgen (H-1, 110 Gpa,.086 g/cm3) silver (Ag-47, 83 GPa, 9.3 g/cm3) gold (Au-79, 78 GPa, 19.3 g/cm3) In general, sound travels faster: in solids than in liquids, in liquids than in gasses **[Speech of sound in the Air]** \(1) **elasticity** is important, but irrelevant because it doesn\'t change appreciably\ (2) **density** doesn\'t change much 1 cubic inch of air contains the mass of about\ 400 billion billion molecules of air (4 × 1020)\ what happens in a much less dense\ gas medium such as helium?\ 1 in3air = 2.12 x 10-5 kg\ 1 in3He = 2.93 x 10-6 kg\ 1 in3Xe = 9.66 x 10-6 kg \(3) **amplitude, frequency, wavelength** play no role in speed\ But, **temperature** plays a role:\ \*\*warmer air molecules have more energy, thus transmitting sound vibrations more quickly. - speed of sound in air is about 1100 ft/s, 335 m/sec, 750 mph\ muzzle velocity 9mm = 1250 ft/s, 381 m/sec, 852 mph - less dense gas\--faster velocity (helium is less dense than air) - more dense solids and liquids\-\--faster velocity - Mach number, speed Ernst Mach (1838-1916) **[Air pressure behavior]** - Made up of many molecules of many chemicals These molecules move: - Constantly in random patterns (Brownian Motion, or drunkard\'s walk; random walk) - At high speeds - into collisions with each other and whatever is in the way - **These collisions produce pressure** - **Brownian motion** = random movement for small collision with other particles **[Air pressure]** - **Pressure:** a force that acts perpendicularly on asurface. - Air pressure can move objects (e.g., wind chimes, ear drum) **[Measurement of Air Pressure]**\ Pressure is calculated by:\ 1. the **force** exerted newton, dyne, kilopound, pound, \...\ 2. the **surface area** on which the force is acting (note that is always 2-dimensional)\ square foot, m2, acre, square inch, mi2, cm2 THUS, giving units of **pressure**:\ PSI (pounds per square inch)\ N/m2 (Newtons per square meter)\ Pa (Pascals) (note: N/m2 = Pa; 1/1,000,000 Pa = μPa)\ dynes/cm2 (dynes per square centimeter) (note: dynes/cm2 = microbar)\ mmHg (millimeters of mercury) Dynes per square centimeter (d/cm2)\ -- Dyne is the unit of force\ -- Cm2 is the unit of area\ -- Generally used for measuring pressure needed to move the eardrum\ Pounds per square inch (psi)\ -- Used to measure larger amounts of force over larger surfaces\ -- Where do we usually see psi measures? car tire: \~30 psi\ bike tire: \~100 psi\ O2 tank: \~2000 psi **[International System of Units]**\ -- Distance, mass, and time\ -- MKS system: meters, kilograms, seconds\ newtons, as in newtons per square meter (N/m2)\ Pascals 1 N/m2 = 1 pascal\ Micropascals (μPa) = 1 millionth of 1 Pa\ -- μPa are more likely to be used for hearing applications\ -- cgs sytem: centimeters, grams, seconds\ E.g., dyne or microbar\ -- Both systems are used\ E.g., air pressure at sea level is measured as 14.7 psi or 1,000,000 d/cm2 in mks or 1,000,000 microbars in cgs. Pressure can also be measured as the amount of force it takes to move a column of liquid in\ a tube.\ -- Cm H2O\ -- 5 cm H2O for 5 second rule\ -- Mercury can also be used, but in mm vs. cm (mmHg) **Higher altitudes = lower pressure** Patmos = sea level is 760 mm Hg or 14.7 psi\ Patmos decreases as altitude increases\ Positive pressure or Ppos \> Patmos\ Negative pressure or Pneg \< Patmos\ For respiration, phonation, and articulation,\ what pressures are we interested in?\ -- Palv\ -- Ptrach\ -- Poral **[Physical Acoustics]** **[Movement of Air]**\ Molecules of air tend to spread themselves around equally\ Thus air will move from an area of **high pressure** to an area of **lower pressure**\ -- This creates a flow -- Flow measures are in volume/time:\ Liters per second (l/s)\ Liters per minute (l/min)\ Milliliters per second (ml/s)\ Milliliters per minute (ml/min) Rate of flow = volume velocity\ -- Speed occurring in a particular direction\ or\ -- speed of a volume of air traveling in a certain direction.\ **Driving pressure** = the difference in pressure which causes air to flow from higher to lower pressure\ -- Important for generating speech - **Laminar flow** = when air molecules flow smoothly in a parallel manner and at the same speed - **Turbulent flow** = flow is random, results in swirls and eddies **[Air Pressure, Volume and Density]** - **Volume** = amount of space occupied in 3D - **Density** = amount of mass per unit volume - **Inverse relationship** = Volume increases, pressure decreases OR Volume decreases, pressure increases - **Proportional relationship** = Both volume and pressure increases or decreases (if temperature is constant) - **Boyle's law** = as volume decreases, the pressure of air increases, given a constant air temperature If the temperature is NOT constant\... - e.g. balloon sizes increase if temperature, pressure, energy added to the system. - At higher temps there is more energy in the system and there are more collisions between molecules. - **Temperature and air pressure are directly proportional** - **Temperature and volume are directly proportional** - **Temperature and density are inversely proportional** **[Changes in Pressure]** **Ambient pressure** (Pam) = the relatively constant pressure that is around us at any time\ -- For sound to be generated the constant Pam must be disturbed by a force\ -- E.g., Striking a tuning fork will create a disturbance resulting in sound - **Mass- Spring Model=** Molecules behave as though they're masses (weights) connected by springs - No energy when the spring is hanging itself - Energy input when you push the spring, friction is created when energy is lost and continues bouncing until it stops. What is the motion of the mass when acted upon a force? - At Rest = dotted line - The cycle decreases as the ball bounces. - **[Sound: changes in air pressure]**\ vibration emanates equally in 3 dimensions spherically, similar to the pressure in a balloon\ exerting equal force everywhere.\ The vibration spreads ***in time***. The leading edge of this energy wave is the **wave front.** - vibration sets off a chain reaction in the movement of the surrounding air molecules - **Compression:** the resulting ***increased density***, which results in an ***increase of pressure***\ -- Moves tympanic membrane inward slightly - **Rarefaction:** the resulting ***decreased density*** of air in the area between the two groups of molecules, resulting in ***lower pressure***\ -- Moves tympanic membrane outward slightly X- axis: Time Y-axis: Pressure **[Elasticity and Inertia]**\ Movement of air molecules eventually come to a resting position\ Two forces come into play\ -- **Elasticity:** the restoring force\ refers to an object springing back to its original size, form, location, and shape after being stretched, displaced, or deformed\ This pertains to all materials (solids, liquids, or gas)\ Thus, once displaced, molecules are trying to move back to their resting position\ **Hooke\'s Law:** elasticity is proportional to and in the opposite direction of displacement. **[Inertia or Newtons\'s First Law of Motion: mass at rest stays at rest, and mass in motion stays]**\ **[in motion unless acted on by outside force.]**\ Inertia causes the molecules to ***overshoot*** their resting position, swinging out farther in the opposite direction\ Elasticity eventually overcomes the inertia\ The swinging back and forth of molecules allows sound to continue after the initial disturbance **[Wave motion]** - Due to the **frictional resistance** of air, each time the molecules swing back and\ forth, their amplitude will decrease (damping). - Same amount of force acting on the swing. - **Damping** is the reduction of amplitude over time **[Coupled oscillators]** - What if you have 2 masses? - If two masses are **coupled**, what happens? - **Huygens\'** clocks on a wall (1665) synchronized. **Phase locking.** - e.g. Also pacemaker and heart cells, running and chewing, crickets chirping in unison, biological cycles **[Characteristics of sound waves]**\ 1. Frequency (f) \[TIME\]\ 2. Amplitude (power, intensity, pressure, level)\ 3. Shape of wave\ 4. Phase (not very important for speech) **[Frequency & period]**\ **Frequency (f)**: A cycle of vibration or pressure change over time (a second, typically). The time to complete a cycle of vibration. cycles per second (cps)\ cycles per second (hertz, Hz) **Period (t)**: the time for one cycle; sec, ms **Wavelength(λ)**: distance between wave fronts; measured in meters (m)\ l.c. **lamda** **[Periodicity]**\ When the frequency of a wave does not change, it is a **periodic** wave. May sound \'musical\' or tonal A wave with variable cycle times (ie, frequency) is **aperiodic**. May sound like noise. No frequency in random noise. **IMPORTANT SLIDE FOR QUIZ** C = speed of sound m/s = meters/second Cy/s = cycle/second m/cy = meters/cycle, not speed of sound A **WAVEFORM** is a picture of a sound wave.\ -- Amplitude (y-axis)\ Peak to peak\ Peak -- Time (x-axis)\ Period Mutiple 50 to get Hz **[Orange line]** 3 cycles in 20m/s 150hz **[Blue line]** 5 cycles in 20m/s 250hz **20 -- 20,000hz hearing** **[Simple Harmonic Motion]**\ Regular, smooth, back and forth movement of molecules.\ A **pure tone** is an SHM. **[Complex waves]**\ **Periodic complex waves** are regular, repeating,\ have fundamental frequency, and have harmonics. **Aperiodic complex waves** are random, do no repeat,\ have no fundamental frequency, and have no harmonics **Complex waves** contain more than one frequency.