Study Guide for SP H 267 at UA
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This 5 page Study Guide was uploaded by an elite notetaker on Friday February 6, 2015. The Study Guide belongs to a course at University of Arizona taught by a professor in Fall. Since its upload, it has received 18 views.
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Date Created: 02/06/15
Descriptions of Sounds Three Standard Descriptions Acoustics the physical properties of sounds are precisely numerically described on paper or computer screens Uses the language of physicals and is detailed Phonetics graphical coding of human speech with specialized symbols phonetic alphabet that describes the nuances of the sounds produced Musical Notation Permits the representation of certain sounds possessing musical features Attack Body and Decay Attack the onset portion of the sound object Sometimes called the quotexcitationquot phase In physics terminology it is in this phase that energy is first put into the sound When the sound first beings there is a rough edge to it the attack The more sudden the attack the more roughness that is present Body the middle portion of the sound that may seem unchanging or unprogressive Many sounds may not have any body eg bells cymbals percussion Decay the portion of the sound object where it dies out or is terminated The sound becomes weaker and weaker until it is gone Some sounds decay rapidly others slowly Types of Information Interaction ofmaterias materials that make up the carsteel plastic rubber vibrate and in turn vibrate the air around it Location as sound waves travel through the air they lose energy especially at high frequencies This can provide information about how far away we are from the source of sound Environment the sound waves that travel from our car to our ears will reflect off various objects in the environment around it Categories of Material Interaction Vibration solids closing a door scraping fingernails across a chalkboard footsteps Changes to the surface of a body of liquid water droplets falling into a pool Aerodynamic changes in the pressure of gases whistle exploding balloon leaky tire Material Properties and Forces Fundamental Physical Quantities Length any measurement of distance is quantified by a length measurement Mass the amount of matter present mass does NOT equal weight Time may be in seconds milliseconds microseconds etc Derived Quantities Area length times width Displacement a change in position Involves both distance and direction Vel0city is a distance traveled in a certain amount of time and in a particular direction Accelerati0n a measure of the change in velocity over time and is given in meters per second Material Properties Mass the amount of matter that is present A mass in motion possesses inertia a force that wants to maintain motion Elasticity stiffness springiness a material property that resists being deformed or moved away from a position of rest a basketball resists being deformed a ball of clay does not When a material with elasticity is deformed it creates a force that quotwantsquot to restore the material to its original shape This force is called a restoring force Material PropertyampForce Elasticity stiffness ampRestoring Force Material PropertyampForce Mass ampInertial Force Friction between objects and Within an objectampconsumes energy and causes vibration to decay Fricti0n opposes motion between the surface of an object and whatever it happens to be resting on Potential Energy stored energy that can be returned at some later time Elasticity may be thought of as the ability of a substance to store potential energy stretching a rubber band Kinetic Energy the energy of motion Inertia can be thought of as the ability to store kinetic energy Motion release of rubber band Tuning Fork as a Vibrating System Four Phases inertia away from the middle elasticity back to the middle friction effects amplitude not frequency 1 Deflecting of the arm mass moves it away from its desired rest position But a restoring force is generated by the stiffness 2 The restoring force stiffness brings the arm mass back to the rest position 3 At this point the arm mass is moving very fast which means there is a large amount of inertia The inertia forces the arm to move through the rest position As it continues to move right to restoring force due to the stiffness is again generated but now in the opposite direction 4 Now the restoring force pushes the arm back toward the rest position But because of the inertia the arm will again move through the rest position and the whole process beings again KTM FT mar f l K M 9 F K We F f Sound Production and Propagation Tuning for vibration sound Pressure forcearea Molecules exert a pressure on any object they come into contact with Sound waves exchange of vibratory motion from air particle to air particle constitutes a sound wave Sound waves are sine waves Peri0dt1F Simple Harmonic Motion SHM Also called sinusoidal motion one cycle of vibration is like going around a complete circle regardless of the frequency Portions of a cycle can be measured as the number of degrees into the cycle this is called the phase angle Mathematically described as a sine wave Phase Instantaneous phase angleThe phase angle at a specific point in time Starting phase angle Phase offset that forces a sine wave to start at some amplitude other than zero Amplitude and Pressure Typical unites ofpressure Newton per square meter Nmquot2 or Pa Peak maximum positive displacement from equilibrium Peak to peak displacement measured from the most negative peak to the most positive peak instantaneous amplitude at some specific instant of ti RMS Calculated root mean squaresquare all pressure values calculate the mean of all the squared pressure values calculate the square root of the values RMS value of sine wave 7071A peak Purpose represents the same pressure that you would feel from a constant pressure source not sound of the RMS value Corresponds to the average mean energy in the sound wave Sound Pressure and Intensity Logarithmic scale because it can compress large ranges of numbers into a more manageable range Power watt W Intensity watt per square meter wattmquot2 DecibelScae Alexander Graham Bell Sound Pressure Measure Sound Pressure Sound Level Meters Absolute sound pressure RMS pressure of a sound wave specified as some number of Pa Relative sound pressure Relative sound pressure is the absolute sound pressure of one sound wave compared to the absolute sound pressure of a second sound Often it is the pressure of some sound quotxquot compared to an absolute reference pressure Pr Doubling ofabsolute pressure an increase in SPL 3dB Doubling ofabsolute pressure is an increase ofiL 6dB Complex Waves and Spectrums Complex Waves any waveform that is not a sine wave is a complex wave All complex waves can be broken down into a set ofsine wave components Fourier Continuous random aperiodic Waveform fundamental period and frequency Amplitude vs Time Spectrum Amplitude vs Frequency Spectral Envelope shape of the spectrum that would result from connecting the amplitudes of the harmonics Auditory System The Ear as a Sound Receiver and Sound Source Passivefilter and open closed resonator Outer Earear canal Frequency Range amplified the most by the combined influences ofouter and middle ear 20004000 HZ Ear drum and pressure high pressure TM pushed inward low pressure TM pulled outward Travelling wave in the ear inner ear cochlea Mechanical Conductor and Amplifier ofsound middle ear increases about 30 dB Tonotopic arrangement basilar membrane Thin end responds to high frequencies middle responds to middle frequencies and wide end responds to low frequencies Inner ear and neural coding stereocilia Cochlear Amplifier outer hair cells refine the sensitivity and frequency selectivity of the mechanical vibrations of the cochlea Outer hair cells change shape when electronically stimulated Otoacoustic Emission small sounds caused by motion of the eardrum in response to vibrations from deep within the cochlea Filters Transferfunction describes how the spectrum of a sound will be altered by passing through the filter PhysicalStructure vocal tract ear musical instruments tunnels halls etc Typical characteristic ofresonantfiters their transfer functions are usually peaked sharp bandpass filters Resonance Constructive Interference two sources producing the same frequency and are in phase Destructive Interference two sources producing the same frequency but 180 degrees out of phase Standing wave occurs when two progressive traveling waves of the same frequency and amplitude travel through the same medium in opposite directions they are called standing waves because the observed wave pattern is characterized by points that appear to be standing still
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