手机声学原理介绍.doc

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 receivers purpose is that the voice messenger is received by the phone ,and the microphones function is that the acoustic information is passed from people to phone .They realize the fundamental function of the phone and perfectly deduce the phones 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 electroacoustics1.1 Sound propagation mode1.2 Speed of sound1.3 Frequency domain1.4 Sound pressure level1.5 Voice three elements2. Acoustics devices of the phones structure3. Working principle of SPK.&RCV.3.1 The basic principle of application3.2 Workong principle3.3 Difference of SPK.&RCV.3.4 The basic parameters of SPK.&RCV.4. The acoustic short circuiting effectText:1. The basic knowledge of the electroacoustics1.1 Sound propagation modeSound transimission needs the medium and sound cant travel through a vacuum .Sound wave belongs to the longitudinal wave1.2 Speed 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 .1.4 Sound pressure level (ear acceptable)SPL is denoted by the sign “Lp” ,whose result is denoted by the sign “db” .SPLs expres-sion is as below : Lp =20 10 P/P0 , P0 - atmosphere pressure P - sound pressure The 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)Sound sourcesSound pressure(pa)SPL(db)The most weak voice able to hear 2*10-50Whispering2*10-340A meters apart speech2*10-260Speech loudly0.280Processing workshop2100Diesel engine20120Jet off2001401.5 Voice 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 , butanyway ,how do these harmonicwaves make up the soundwave ? How is their result ? Canneither make the substantial explanations ,can nor make a measure .So ,for the tone ,people feel completely by heart and with experience ,and it is mans subjective opinion .2. Acoustics devices of the phones 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 application For 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 principle The 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 cutthe 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 transformationfrom the Electricity to the Force ,and to the Sound, again.3.3 Difference of SPK &RCV SPK is heared by the ear through a distance ,while RCV is directly heared .SPKs worki-ng range is wide , involving the music category , while working range of RCV is the voice . SPKs power is bigger than RCVs . SPKs geometry is bigger than RCVs. Also , SPK is quite arbitrary in phones position ,but RCV is only in a position .3.4 The basic parameters of SPK.&RCV. Frequency Response curve Effective Frequency Range SPL(Sound Pressure Level) THD(Total Harmonic Distortion) F0 - Harmonic Frequency Rated impedance Rated Power / max. Power4. The acoustic short circuiting effect When vibrating diaphragm of SPK and RCV vibrates ,they will generate the soundwaveforward and backwad , and their soundwaves phase is the opposition . Because directivity oflow frenquency is more than 180 degrees ,close to no directivity , when soundwaves outwardshow a