1、 Functional characteristics of loudspeaker
Speakers, commonly known as loudspeakers, are indispensable and important devices in sound systems. All music is transmitted to the human ear through loudspeakers. They are electroacoustic devices that can convert electrical signals into sound waves.
The loudspeaker is mainly composed of magnetic circuit system and vibration system. The magnetic circuit system is composed of a ring magnet, a magnetic column and a magnetic guide plate; The vibration system is composed of paper basin, paper basin support, voice coil, voice coil support, etc., as shown in the figure.
Note: The voice coil is made of enamelled wire, and the number of turns is very small (usually only ten), so the impedance is very small. The outgoing line of the voice coil is flat against the paper basin, and the glue is stuck on the paper basin. The paper basin is made of special molded paper, and a dust cover is added in the center to prevent dust and debris from entering the magnetic gap and affecting the vibration effect.
When the voice coil of the loudspeaker is connected with the common frequency current, the voice coil will generate an alternating magnetic field under the action of the current, and the coil will vibrate in the magnetic field formed by the permanent magnetic steel. Because the size and direction of the magnetic field generated by the voice coil change with the change of the audio electrical signal, the interaction of the two magnetic fields makes the voice coil move perpendicular to the current direction of the voice coil. Because the voice coil is connected with the vibration membrane, the voice coil drives the vibration membrane to vibrate, and the vibration of the vibration membrane causes the air to vibrate and produce sound.
2、 Detection method of loudspeaker
When using a multimeter to detect the loudspeaker, you can determine whether the loudspeaker is damaged by detecting the resistance of the loudspeaker. Before testing, the nominal AC impedance value of the loudspeaker to be tested can be known to provide a reference standard for testing, as shown in the figure.
Measure the resistance between the two output pins of the loudspeaker with a multimeter, and judge whether it is good or bad according to the test results, as shown in the figure.
Note: It should be noted that the nominal resistance value 89 on the loudspeaker refers to the resistance value of the loudspeaker when it is driven by normal AC signal, that is, the AC resistance value; When the multimeter detects, the measured resistance is DC resistance.
Under normal conditions, the DC resistance should be close to and less than the nominal AC resistance. If the measured resistance is zero or infinite, the loudspeaker is damaged and needs to be replaced.
In addition, if the loudspeaker has good performance, during the test, place one probe of the multimeter on one or two terminals of the loudspeaker. When the other probe touches the other terminals of the loudspeaker, the loudspeaker will emit "coffee"; If the speaker is damaged, there will be no sound. In addition, in case of coil adhesion or jamming, paper basin damage, etc. in the loudspeaker, it cannot be identified with a multimeter, and it can only be identified by listening to the sound effect.
