手机声学原理介绍

Learning report on principles of acoustics of the cellphoneZHOU Yang-fangOnce in the Sunlite Electronic (Shen Zhen ) co.,ltd, Shen Zhen 518000, ChinaAbstract:These days , through the chect of kinds of material ,I have a general idea of the mobile phone acoustics and make a relavant arrangement ,making mainly a summary report in here .The sound system of the phone have the three basic function devices that include the speaker ,the receiver ,and the microphone .The speaker is to realize the hand-free cellphone conversation and the speech broadcasting ,the receiver’s purpose is that the voice messenger is received by the phone ,and the microphone’s function is that the acoustic information is passed from people to phone .They realize the fundamental function of the phone and perfectly deduce the phone’s roles in the daily life so that we cannot do without it .Keywords:Acoustics of the cellphone ,acoustics devices ,sound wave , the working principle ,short circuiting effectContent:1.The basic knowledge of the electroacoustics1.1Sound propagation mode1.2Speed of sound1.3Frequency domain1.4Sound pressure level1.5V oice three elements2.Acoustics devices of the phone’s structure3.Working principle of SPK.&RCV.3.1The basic principle of application3.2Workong principle3.3Difference of SPK.&RCV.3.4The basic parameters of SPK.&RCV.4.The acoustic short circuiting effectText:1.The basic knowledge of the electroacoustics1.1Sound propagation modeSound transimission needs the medium and sound can’t travel through a vacuum .Sound wave belongs to the longitudinal wave1.2Speed of soundSpeed which sound travels through the air is 344 m/s ,at normal temperatures and press- ures.The highter the temperature is ,the greater the sound velocity is .And sound travels faster in the liquid and the solid than through the air .The relationships of sound speed through the air and temperature is that , c (t℃) =331.6 +0.6t m/s1.3 Frequency domainUaually,frequency range is 20 HZ to 20K HZ .The soundwave ,whose range is below 20 HZ,is called the infrasonicwave ,while the soundwave whose range is above 20K HZ is called the ulfrasonicwave .But the range of speech tone is 300 HZ to 3400 HZ .1.4Sound pressure level (ear acceptable)SPL is denoted by the sign “Lp” ,whose result is denoted by the sign “db” .SPL’s expres- sion is as below :Lp =20 ㏒10 P/P0 , P0 --- atmosphere pressureP -- sound pressureThe relationships of sound pressure and sound pressure level is that ,the sound pressure e- very double and the increased sound pressure level 6db ,and every increase 10 times and incr- eased pressure level 20db . As provided below ;P0 = 1.0325 ×105(20℃)1.5Voice three elementsThe pitch ,the volume ,and the tone make up three elements of voice . The pitch repre-- sents the high-low of sound frequence ,whose result is denoted by the sign “CPS “(cycle per second) .The volume represents the big or small of sound amplitude ,usually denoted by the sign “db” . For the soundwave ,people only know it is generated by the harmonicwave , but anyway ,how do these harmonicwaves make up the soundwave ? How is their result ? Can neither make the substantial explanations ,can nor make a measure .So ,for the tone ,people feel completely by heart and with experience ,and it is man’s subjective opinion .2.Acoustics devices of the phone’s structureUsually the cellphone acoustics devices include the miniature receiver ,the polyphonic speaker ,the microphone ,and the headsets .3.Working principle of SPK.&RCV.3.1 The basic principle of applicationFor SPK and RCV ,their application basic principle ,including threee parts of Electricity ,Magnetism ,and Force ,is that when the current-carrying wire cuts the line of magnetic force ,it will exposure to the power of magnetic field with its forced direction following the Left Hand Rule ,and the valve of force is that F= BIL .3.2 Working principleThe SPK and RCV ,their magnetic circuit system consists of the annular space in which is full of uniform magnetic field , whose vibrating system is made up of the ring voice coil constituted the conducting wire and the vibrating diaphragm liked with it .Their working pri- nciple is that ,as the voice coil is transmitted a signal voltage ,it will generate current and cut the line of magnetic force ,and then generate the force ,on the effect of which , the vibrating diaphragm will generate the vibration and then compress the atmosphere air ,as a result that , the SPK and RCV generate the sound . For the overall process above , it is a transformation from the Electricity to the Force ,and to the Sound, again..3.3 Difference of SPK &RCVSPK is heared by the ear through a distance ,while RCV is directly heared .SPK’s worki- ng range is wide , involving the music category , while working range of RCV is the voice .SPK’s power is bigger than RCV’s . SPK’s geometry is bigger than RCV’s. Also , SPK is quite arbitrary in phone’s position ,but RCV is only in a position .3.4 The basic parameters of SPK.&RCV.Frequency Response curveEffective Frequency RangeSPL(Sound Pressure Level)THD(Total Harmonic Distortion)F0 --- Harmonic FrequencyRated impedanceRated Power / max. Power4.The acoustic short circuiting effectWhen vibrating diaphragm of SPK and RCV vibrates ,they will generate the soundwave forward and backwad , and their soundwaves phase is the opposition . Because directivity of low frenquency is more than 180 degrees ,close to no directivity , when soundwaves outward show a ring spread ,soundwaves of anti-phase low frequency will intersect forward and bac- kward , and then voice willl take place of short circuit . This is the acoustic short circuiting effect .Phone’s cavity and gasket can avoid the acoustic short circuit effect ,separating sound waves brfore and after .。