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Sound Transmission- Reflection, Refraction, and Diffraction.docx

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Department
Psychology
Course Code
PSYCH 3A03
Professor
Paul Faure

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September 18 , 2013 Psych 3A03: Audition Sound Transmission: Reflection, Refraction, and Diffraction Sound Pressure and Energy - ( ) - Sound pressure (p) is proportional to air particle velocity - Air particles vibrate due to input force.: work is done - Energy (E): ability to do work - Power (P): rate of energy transfer through medium - Power = Work/time - Power = Energy transfer/time - Energy = Power x time Sound Energy (units: joule = Nm) - In sound transmission, energy flows through medium - Energy: ability to do work  Units of energy = Joule (J); 1J = 1Nm Sound Power (units: watts) - Power: rate of energy transfer through a medium - Power is the rate at which work is accomplished  Power – work/time  Power = energy transfer/time  Energy = power x time - Units of power: watt - The Watt was named after James Watt who invented the stem engine - 1 Watt = 1 J/s = 1 Nm/s Energy vs. Power - Energy is the ability to do work  Energy flows through medium - Power: rate of energy transfer through a medium  Power is the rate at which sound is accomplished - Power and energy are proportional to each other, but they are not equivalent measures Sound Intensity (units: watts/m ) 2 - Acoustical energy is transmitted outward form a point source in an expanding spherical wave form - To measure its acoustic power (J/s), we would have to integrate over the entire spherical surface - Vector - Often we are only interested in the amount of power that acts upon or passes through a certain, smaller pre-defined area, such as one square meter - Sound intensity is the amount of energy (J) that is transmitted per second (1 watt = 1J/s) over or through an area of one square meter in a specified direction (vector quantity) - Units of intensity: watt/m = J/sm 2 - Absolute measures Absolute versus Relative Acoustic Measures - Measure hearing thresholds and how they vary within a person as a function of frequency; or between persons - Measures of power (watt), intensity (watt/m ) and pressure (Pa) are absolute measures - In audition we are often interested in relative measures of sound power, intensity and/or pressure - Relative acoustic measures compare the power, intensity, or pressure of an incident sound against the power, intensity, or pressure of a reference sound - Relative acoustic measures employ levels: L = Inference/standard Levels = Ratio of Absolute Sound Energy - Relative acoustic measure compare the power, intensity, or pressure of an incident sound vs. the power, intensity, or pressure of a reference sound - Levels measures employ a ratio to compare the power, intensity, or pressure of an incident sound with the power, intensity, or pressure of a standard reference sound - Level = Power /Power incident reference - Levels are very useful because large numerical ranges are now expressed with small numbers - Measures of levels are not very useful unless the reference value is specified or when working with large numbers The Bel (bel) - The human ear has a very large dynamic range(10 -10 intensity units) - Such large intensity ranges are cumbersome but can
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