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sound transmission

QuestionAnswer
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.
Created by: GHAIDEE on 2008-07-19



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