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sound transmission

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pressure   force distributed over a particular area measure in dynes/cm2 or pascals (Pa) in order for sound to occur a vibrating object has to cause change on pressure this vibration is the transmitted through a medium (air) to our ears.  
Static Air Pressure   created by the presence of molecules in the air. molecules in the air are always moving which causes them to collide. The motion is called BROWNIAN MOTION. the sound that is transmitted is called thermal noise 20-30dB below faintest human sound (insects  
Sound propagation   in air the molecues next to the sound source move first then they pass the motion to the following molecules. the motion is the transferred from air to ear.  
condensation   molecules next to the vibration are compressed creat an area of high density and high pressure  
rarefraction   molecules not next to the vibration have low pressure low density.  
instantenous pressure   pressure that vibrating object exerts on an area. pressure =force/area ) intensity of asound  
DECIBEL   human ear can hear a wide range of sound intensities from .0002 dyne/cm2 to 2,000,000 dynes/cm2 but its easier to use a log scale it is more mangeable bc the ranges in the scale is fm 0-140dB. it would be hard to represent this in a linear scale. adding  
REFERENCE POINT or ZERO POINT   the reference point is traditionally .0002 dyne/cm2 in the log scale it will be 0dB this does not meand there is no sound. if an intensity of a tone is -10dB that means that it is 10dB lower that the reference point. the formula is dB SPL= 20 x log press  
SOUND TRANSMISSION IN A SOUND FIELD   theres is only a few anechoic rooms, most fields reflect sound REVERBRATION- continous reflected sond that prolong the existence of an intial sound. REVERBRATION TIME- is the time it take for the reverbrant sound to die down. th elonger it take the loude  
INVERSE SQUARE LAW   when there is no obstacles the farther away the person is form the sound source the softer they are going to hear it. if the distance is double the sound intesity decreased by 6dB  
INTERFERENCE   some portion of sound might be absorbed some might be relfected. CONSTRUCTIVE  
IMPEDANCE   when there is an obstacle such like mass stiffness and resisstance this creates impedance. two types. REACTANCE (caused my mass and stiffness) RESISTANCE (caused by friction)  
SOUND SHADOW   an area of decreased intensity beyond the object. decreases the sound. when an obejct is smaller that the wavelength it does not affect the wave motion but when the object is larger than the wavelength it cuases the movement of wave to be reflected.  
STANDING WAVE   stationary pattern of waves produced by two waves of the same frequency traveling in opposite directions on the same transmission line. when a wvaelength of resonance frequenct and wavelgnth of tested frenquect singal is same they cancel out signal.  


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