Amateur testing of common electroacoustic devices

1. Dynamic Coil Speaker From the appearance structure, check whether the iron frame of the speaker is rusted from the appearance; whether the paper basin is damp, moldy, or broken; whether the lead wire is disconnected, unsoldered, or virtual welded; whether the magnet is dropped, cracked, or displaced; use a screwdriver to approach the magnet Check the strength of its magnetic force.
2. To judge the positive and negative polarities, put the multimeter in the 0.5mA block, connect the two meter rods to the two soldering pieces of the speaker to be tested, and lightly press the paper cone of the speaker with your fingers to make the coil connected to the paper cone cut in the magnetic steel When the magnetic field lines move, an induced current will be generated, and the direction of the pointer deflection can be observed from the multimeter. If the pointer is deflected in a clockwise direction, the end to which the black watch stick is connected is positive, otherwise it is negative.
3. Coil and Impedance Test Put the multimeter in R × 1 block, touch the terminals with two bars (regardless of positive and negative poles), and hear the obvious “gurgle” sound, indicating that the coil is not broken. Look again at the place where the needle stays, if the measured impedance is close to the marked impedance, it means that the speaker is good; if the actual resistance value is much smaller than the nominal resistance value, it means that the speaker coil has a short-turn between turns; if the resistance value is ∞, it means that The internal circuit of the coil is broken, or the terminal may be disconnected, unsoldered, or virtual welded.
4. Detection of sound distortion (1) Cracked paper cone The paper cone is an important part of sound, and it is important to check whether the paper cone is damaged. When the speaker cone breaks, there will be a "squeak" sound when playing; if the cone is badly damaged, it will be bitten by insects, the damage area is large, and it can not be repaired and discarded.
(2) The voice coil and the magnetic steel collide. The voice coil moves in the magnetic gap of the magnetic steel, and there are more chances of damage. You can use your fingers to gently press the paper cone. If the paper cone is difficult to move up and down, it means that the coil is stuck by the magnet. There are two reasons for this: one is that the magnetic core is shifted after the speaker falls; the other is that the paper cone and the connected coil are shifted or deformed, causing the voice coil to rub against the magnetic steel when vibrating, making the sound Questions or no sounds can be made. The lighter ones cause the sound to rustle and distort, while the more severe make the voice coil loose or disconnected.
2. Piezoceramic speakers 1. Check the appearance. Piezoceramic speakers, also known as crystal speakers, mainly check whether the surface of the piezoelectric sheet is damaged or cracked; whether the leads are de-soldered or virtual welded.
2. Detection of "piezoelectric effect" It is not easy to measure its DC impedance with a multimeter, but it can be skillfully detected by the reverse process of "piezoelectric effect". Put the multimeter in the micro-ampere block, the positive and negative poles of the two meters are connected to the two poles of the piezoelectric plate, and then use the rubber tip of the pencil to gently press the piezoelectric plate placed on the desktop or the glass plate, Observe whether the pointer of the meter swings. If there is obvious swing of the hands, it indicates that the piezoelectric sheet is intact, otherwise the piezoelectric sheet will fail.
3. Moving Coil Microphone In terms of appearance and structure, the method of first-in and second-out should be adopted. If distortion occurs, first check whether the voice head is damp and whether the voice coil and the magnetic steel collide; then use a multimeter to check the voice coil impedance and nominal Whether the values ​​are similar. If there is no sound, first check whether the voice coil wiring is loose or poor contact; then use a multimeter to check whether there is continuity. It should also be checked whether the switch is loose; whether the plug is unsoldered; whether the core wire and shielded wire of the cord are broken, etc., and the appearance of the fault can be found through the appearance and electrical inspection.
2. Judgment of silent failures For general microphones (such as household karaoke microphones), the DC resistance is 600 ± 10Ω. Using a multimeter R × 100, test the center end of the plug and the case, turn on the microphone switch and turn it on, the resistance should be 600Ω. If the impedance cannot be measured, it means that the microphone is disconnected from the plug → switch → sound head, which can be detected with a multimeter. First unscrew the front cover and directly measure the two ends of the lead wire of the voice head. If R = ∞, it proves that the voice coil is open. If R = 600Ω, it proves that the voice coil is good. The phenomenon of open circuit often occurs: for example, the shielded network cable of the wire rope is easily broken, the core wire is unsoldered; the internal contact of the switch is poor or the wiring is unsoldered, etc.
3. Detection of light sound and distortion First unscrew the front cover of the sound head and observe whether the diaphragm is flattened or elastic. Use a multimeter R × 1 block, the two meter sticks touch the two ends of the sound head, the bitter sound is very small, switch to R × 100 block, and measure the impedance. If the impedance is about 300Ω, it means that there is an inter-turn short circuit inside the voice coil, resulting in electricity Magnetic induction drops. If there is an obvious "rustle" sound at the two terminals of the touch head, it proves that the friction sound generated by the collision of the voice coil and the magnetic steel indicates that the position of the voice coil or diaphragm has changed and cannot be used. If no other faults can be found, the magnetic properties of the magnet are generally reduced, and only the sound cartridge needs to be replaced.
4. Judgment of the occurrence of severe howling Howling is a common failure of microphones. According to practical experience, there are several reasons: ① The shielded network cable in the wire rope is broken or the shielded wire connected to the plug falls off, only its core wire is normal. When the microphone plug is inserted into the jack of the power amplifier, because the shielding wire is disconnected, which is equivalent to the grounding wire also being disconnected, the human body induction or external interference of the microphone in hand will be transmitted to the loudspeaker to generate self-oscillation and howl. ②After replacing the sound head, the core wire and shielded wire in the wire rope are led to the sound head through the toggle switch, and it is easy to cause the center line to dock with the ground end of the power amplifier, and the shield wire is connected to the power amplifier. Input. For the microphone of the plastic cylinder shell, no problem can be found, and no howling will be generated, but for the microphone of the metal cylinder shell, because the metal shell is held by the center line of the hand, the human body induction is introduced into the power amplifier to produce howling. It can be tested with a multimeter R × 100, and the lead wire at one end of the sound head is welded away to avoid the formation of a loop; then the switch is placed in the "ON" position, if it is placed in the "OFF" position, it is equivalent to the short of the center line and the shield line It forms a loop and affects the test. At this time, connect the center end of the plug to the metal shell of the microphone with a multimeter. At this time, it should not be connected, indicating that the core wire is not connected to the handheld metal part, which prevents human body induction. The shielded wire terminals of the plug are connected, so that the grounded part of the power amplifier is held in hand, and howling will not occur.
4. Electret microphone (microphone)
Rotate the multimeter to R × 100, connect the metal shielding net of the microphone with the red meter bar, and connect the core wire with the black meter bar, which is equivalent to adding a positive voltage to the internal field effect tube drain. At this time, the multimeter pointer should be pointed at On a certain scale, and then blow into the microphone. If the pointer does not respond, you may use the watch bar to change the detection. If you still do not respond when blowing into the microphone, you may think that the electret is damaged by leakage. If you blow into the microphone, the pointer will swing to a certain extent, indicating that the electret microphone is intact. If you directly test the microphone lead wire for no resistance, it means that the internal electret is open; if the resistance is zero, it means that the electret is short-circuited; if the electret is intact, you should carefully check whether the external lead wire is broken or short-circuited. var check_allow = "/d/Api/iscantalk.html"; var add_url = '/ d / article / write /'; function CheckLogin () {now_uid = ''; var ElecfansApi_checklogin = '/ webapi / passport / checklogin'; var logout_url = "{: U ('Login / logout')}"; var logout_url = 'http://bbs.elecfans.com/member.php?mod=logging&action=logout&refer=front'; $ .get (ElecfansApi_checklogin, function (data, textStatus) {if (data! = "") {EchoLoginInfo (data); CheckEmailInfo (data); data = $ .parseJSON (data); now_uid = data.uid; / * var login_content = 'write an article