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Sound Intensity and Pressure.docx

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Paul Faure

September 13 , 2013 Psych 3A03: Audition Sound Intensity and Pressure Frequency - Measured in Hz - Number of cycles per second Wavelength - Spatial difference between two identical points is a wavelength - Represented by λ - Can be expressed in space or time - λ = c/f = 344ms/cycles/s; λ = m/cycle - Wavelength is a distance - Wavelength is a scalar quantity (it has magnitude only) - Sound of higher frequency have shorter wavelengths - Sounds of lower frequency have longer wavelengths - The speed of sound propagation trough the medium also affects the sound wave Starting Phase - Starting phase is the point in the displacement cycle at which the object begins to vibrate - Units of phase = degrees ( ) [also radians (π=rad)] - Phase angle varies from 0 -360 [0-2π radians] - All sinusoids must have a starting phase angle Phase Difference - Starting phase is relative to 0 (start of waveform) - Two sinusoid of the same frequency with different starting phases are said to be out of phase - The phase difference between two sinusoids of the same frequency is determined by examining any two points along the time axis Instantaneous Phase - Instantaneous phase is the phase angle of a signal at any given point in time - Phase difference is not constant; changing as a function of a sine wave - 2 signals of the same frequency can have an instantaneous phase difference when their starting phases differ - 2 signals of different frequency can have an instantaneous phase difference when the starting phases are the same - Cosine is a sine wave with a starting phase of 90 o - Cosθ = sin(90 -θ) Speed of Sound (c) - Rate of air particle vibration is characteristic of the sound source, but the speed at which sound propagates is a characteristic of the medium - Sounds of different frequencies propagating through a medium travel at the same speed (i.e., sound frequency and sound speed are independent variables) - The medium dictates the speed of sound - The speed of sound is given by  √ ⁄ (units: m/s), where E is elasticity and ρ is the density  E = the elasticity of the medium, how quickly the particles return to their original state (Pa or Nt/m )  Ρ = den3ity of the medium, how many particles there are (kg/m ) - The speed of sound changes with temperature such that  C = 331.4 + 0.607T (units: m/s)  Where T = ambient temperature of the medium ( C) o o 8  Thus, at 21 C, c = 344m/s (speed of sound), speed of light = 3x10 m/s
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