Speakers are divided into built-in speakers and external speakers, and external speakers are generally called speakers. The built-in speaker refers to the built-in speaker of MP4 player, so that users can hear the sound of MP4 player not only through the headphone jack, but also through the built-in speaker. MP4 player has built-in speakers, which can avoid the inconvenience caused by external speakers and wearing headphones for a long time.
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(1) The speaker has two terminals (two leads). When a single speaker is used, the two pins have no positive polarity or negative polarity, and when multiple speakers are used at the same time, the two pins have polarity.
(2) The speaker has a paper basin, which is usually black and white.
(3) There are two kinds of speakers: round and oval.
(4) The back of the paper basin of the speaker is a magnet, and the external magnetic speaker will feel the presence of magnetism when touching the magnet with a metal screwdriver; The built-in magnetic speaker does not feel this way, but there is a magnet inside the shell.
(5) The loudspeaker is installed on the machine panel or in the sound box.
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Speaker is a kind of transducer that converts electrical signals into acoustic signals, and its performance has a great influence on sound quality.
(1) Type of speaker
There are many kinds of speakers, which can be divided into electric (that is, moving coil type), electrostatic (that is, capacitive), electromagnetic (that is, reed type) and piezoelectric (that is, crystal type) according to their energy conversion principle, and the latter two are mostly used in rural cable broadcasting networks; According to the frequency range, it can be divided into low-frequency speakers, medium-frequency speakers and high-frequency speakers, which are often used as combined speakers in sound boxes.
(1) low-frequency speaker
For different speakers, the requirements for low-frequency speaker quality factor-Q0 value are different. For closed box and inverter box, Q0 value is generally between 0.3 and 0.6. Generally speaking, the larger the aperture, magnet and voice coil diameter of the low-frequency speaker, the better the low-frequency playback performance and transient characteristics, and the higher the sensitivity. The structural form of bass unit is mostly cone-basin type, and a few are flat-plate type. There are many kinds of diaphragm for bass unit, including aluminum alloy diaphragm, aluminum-magnesium alloy diaphragm, ceramic diaphragm, carbon fiber diaphragm, bulletproof cloth diaphragm, glass fiber diaphragm, propylene diaphragm, paper diaphragm and so on. Generally, the bass units of aluminum alloy diaphragm and glass fiber diaphragm have small diameter ratio and bear large power, while the bass units of reinforced paper basin and glass fiber diaphragm have more accurate timbre and good overall balance when playing back music.
(2) Intermediate frequency speaker
Generally speaking, if a loudspeaker has a flat frequency response curve, its effective frequency response range is larger than its sound band width in the system, and its impedance is consistent with its sensitivity and low frequency unit. Sometimes the power capacity of the midrange is not enough, so we can choose a midrange with higher sensitivity and impedance, thus reducing the actual input power of the midrange unit. Alto units generally have two types: cone basin and dome. However, its volume and endurance are larger than that of the high-pitched unit, and it is suitable for playing medium audio. The diaphragm of the alto unit is mainly made of soft materials such as paper basin and silk membrane, and occasionally there is a small amount of alloy dome diaphragm.
(3) High frequency speaker
As the name implies, a tweeter is a speaker unit for playing high-frequency sound. Its structural forms mainly include numerical solution type, cone-basin type, spherical top type and aluminum strip type.
(2) The structure and working principle of the electric loudspeaker.
Electric speakers are widely used, which can be divided into three types: paper basin type, horn type and dome type. Only the first two are introduced here.
1, paper basin speaker
Paper cone speaker is also called dynamic speaker.
It consists of three parts: ① vibration system, including cone-shaped paper basin, voice coil and centering bracket; (2) Magnetic circuit system, including permanent magnet, magnetic conducting plate and exciting stem; (3) Auxiliary system, including basin frame, wiring board, blank holder and dust cover, etc. When an audio current flows through the voice coil in the magnetic field, it will generate a magnetic field that varies with the audio current. This magnetic field interacts with the magnetic field of the permanent magnet to make the voice coil vibrate in the axial direction. Because the speaker has simple structure, full bass, soft sound quality, wide frequency band and low efficiency.
2. Small speakers
The structure of loudspeaker is composed of vibration system (tweeter) and loudspeaker. The vibration system is similar to a paper basin speaker, except that its diaphragm is not a paper basin, but a dome-shaped diaphragm. The vibration of the diaphragm radiates sound waves into the air through the horn (after two reflections). With high frequency and loud volume, it is often used for outdoor and square field sound reinforcement.
(3) Main performance indicators of the loudspeaker
The main performance indicators of the loudspeaker are: sensitivity, frequency response, rated power, rated impedance, directivity and distortion.
1, rated power
The power of speakers can be divided into nominal power and maximum power. Nominal power is called rated power and undistorted power. Refers to the maximum input power of the speaker within the rated undistorted range, and the power marked on the trademark and technical specification of the speaker is the power value. The maximum power refers to the peak power that the speaker can bear at a certain moment. In order to ensure the reliability of the gyro, the maximum power of the speaker is required to be 2~3 times of the nominal power.
2. Rated impedance
The impedance of a loudspeaker is usually related to the frequency. Rated impedance refers to the impedance measured from the speaker input when the audio frequency is 400Hz. Generally, it is 1.2~ 1.5 times of DC resistance of voice coil. The common impedances of general moving-coil speakers are 4 Ω, 8 Ω,16 Ω, 32 Ω, etc.
3. Recording and playback amplitude-frequency response
When audio signals with the same voltage but different frequencies are applied to the speaker, the generated sound pressure will change. Generally, the sound pressure produced by middle audio is relatively high, while the sound pressure produced by low audio and high audio is relatively low. When the sound pressure drops to a certain value of the intermediate frequency, the high and low frequency range is called the frequency response characteristics of the speaker.
The ideal speaker frequency characteristic should be 20~20KHz, so that all audio can be reproduced evenly, but this is impossible. Each speaker can only play back a certain part of the audio well.
Step 4 deform
The phenomenon that the speaker cannot reproduce the original sound realistically is called distortion. There are two kinds of distortion: frequency distortion and nonlinear distortion. Frequency distortion is caused by strong playback at some frequencies and weak playback at other frequencies. Distortion destroys the original proportion of high and low sound levels and changes the original timbre. The nonlinear distortion is due to the fact that the vibration of the speaker vibration system is not completely consistent with the fluctuation of the signal, and a new frequency component is added to the output sound wave.
5. Pointing characteristics
It is used to characterize the sound pressure distribution characteristics radiated by speakers in all directions in space. The higher the frequency, the narrower the directivity, and the larger the paper basin, the stronger the directivity.
Use of speakers
According to the field reflection used and the requirements for sound, speakers are selected according to the characteristics of each speaker. For example, for outdoor audio-based broadcasting, an electric drum speaker can be used. If high sound quality is required, an electric speaker or sound column should be used. For general indoor broadcasting, you can choose a small speaker made of electronic paper basin speakers. For music-based or high-quality audio amplification, you should choose a sound box composed of high-pitched and low-pitched speakers.
Pay attention to the following points when using speakers and corresponding:
(1) Do not get more power than its rated power, or the voice coil will be burned or scattered. The working voltage of electromagnetic and piezoelectric ceramic speakers should not exceed 30V.
(2) Pay attention to the impedance of the speaker to match the output line. Please refer to the amplifier section for details.
(3) Correct selection of speaker model. If you use it in the square, you should choose a tweeter; Paper basin speakers and auxiliary speakers should be selected for indoor use. High and low speakers can also be made into successful speaker groups to expand the frequency response range.
(4) When arranging the speakers, the sound should be uniform and the sound level should be sufficient. If a single (point) speaker can not meet the needs, it can be set at multiple points, so that every listener can get almost the same loudness and improve the clarity of the sound; To have a good sense of orientation, the speakers should be installed more than 3 meters above the ground, so that the audience can "see" the speakers, and try to make the hearing (sound source)-vision (speakers) in the horizontal direction as consistent as possible, and the distance between the two speakers should not be too large.
(5) The electric horn speaker can only be used after the horn is installed on the sound head, otherwise it will easily damage the sound head.
(6) When two people use the loudspeaker together, they must pay attention to the phase problem. If it is reversed, the sound will be obviously weakened. The easiest way to measure the speaker phase is to connect the test meter with the connector of the speaker with the 50~250μA current of a high-sensitivity meter or multimeter, and then hold the paper basin with both hands and push it hard, so that their phases can be measured from the swing direction of both hands. If the phases are the same, the pointer swings in one direction. At this time, the voice coil lead connected with the positive stylus can be regarded as "ten" level.
Edit this paragraph parameter.
The parameters of the loudspeaker refer to the specific performance parameters of the loudspeaker tested by a special loudspeaker testing system. Commonly used parameters are: z, Fo, η0, SPL, Qts, Qms, Qes, Vas, Mms, Cms, Sd, BL, Xmax, Gap gauss. The following are their physical meanings.
Z: refers to the resistance value of the speaker, including rated impedance and DC impedance (unit: ohm/ohm), usually referring to rated impedance.
This is the basis for calculating the electric power of the loudspeaker.
DC impedance DcR: refers to the impedance value measured by applying DC signal when the voice coil is stationary. We usually say 4 ohms or 8 ohms refers to the rated impedance. (ACR AC impedance: voice coil resistance measured under dynamic conditions)
Fo (lowest * * * vibration frequency) refers to the frequency corresponding to the first maximum value of the loudspeaker impedance curve.
Unit: Hertz (Hz) The impedance curve of the loudspeaker is the curve that the impedance mode of the loudspeaker changes with frequency, which is measured by constant current method or constant voltage method under the normal working conditions of the loudspeaker.
η0 (loudspeaker efficiency): refers to the ratio of output sound power of loudspeaker to input electric power.
SPL (sound pressure level): refers to the situation when the rated impedance of the horn is1w. Point on the reference axis from the horn1m.
Unit: generated sound pressure, in decibel (dB).
Qts: total quality factor of loudspeaker.
Qms: mechanical quality factor of loudspeaker.
Qes: Electrical quality factor of loudspeaker.
Vas (speaker effective volume): refers to the volume when the soundness of air enclosed in a rigid container is equal to the soundness of the speaker unit.
Mms (Vibration Mass): refers to the total mass of all parts of the speaker that participate in vibration during the movement, including the drum paper part, voice coil and elastic wave.
Unit: gram. And air quality related to vibration.
Cms (force flexibility): refers to the flexibility of the supporting parts of the speaker vibration system. The larger the value, the softer the whole vibration system of the loudspeaker.
Unit: mm/Newton (mm/Newton)
Sd (vibration area): refers to the effective vibration area of the drum paper/diaphragm when the speaker vibrates. Unit: m2.
BL (magnetic force): the product of air gap magnetic induction intensity and effective voice coil line length. Unit: (T*M).
Xmax: Linear stroke of voice coil during vibration. Unit: millimeter (mm).
Gap Gaussian: gap magnetic induction intensity value. Unit: Tesla.
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Low-grade plastic speakers can't overcome resonance and have no sound quality because of their thin boxes (some designed plastic speakers are far better than inferior wooden speakers); Wooden speakers reduce the sound pollution caused by box resonance, and the sound quality is generally better than that of plastic speakers.
Generally, multimedia speakers are designed with two units and two frequency dividers. A smaller speaker is responsible for the output of medium and high notes, and another larger speaker is responsible for the output of medium and low notes.
The materials of these two kinds of speakers should be considered when choosing speakers: the high-pitched unit of multimedia active speakers is mainly soft dome (in addition, there are titanium domes used to simulate sound sources, etc.). ), combined with digital audio source, can reduce the stiffness of high-frequency signals, giving people a gentle, smooth and delicate feeling. Nowadays, many multimedia speakers use soft balls such as silk film with good quality and PV film with low cost.
Bass unit, which determines the sound characteristics of the speaker, is relatively important to choose. The most common ones are as follows: paper basin, gummed paper basin, paper-based wool basin, pressing basin and so on.
Paper pots have natural timbre, low price, good rigidity, light material and high sensitivity, but the disadvantage is poor moisture resistance, and it is difficult to control consistency when making. But there are paper pots everywhere in the top HiFi system, because the sound output is very uniform and the degree of reproduction is good.
Bulletproof cloth, with wide frequency response and low distortion, is the first choice for people who like heavy bass. The disadvantages are high cost, complicated production process, low sensitivity and poor light music effect.
Wool woven basin, soft in texture, performs very well in light music and light music, but the bass effect is not good, lacking strength and shock.
PP (polypropylene) basin, widely used in high-grade speakers, has good consistency, low distortion and remarkable performance in all aspects. In addition, fiber diaphragm and composite diaphragm are rarely used in public speakers because of their high prices.
The larger the speaker size, the better. Large-caliber bass units perform better at low frequencies and can be selected when purchasing. A sound box made of high-performance speakers means lower transient distortion and better sound quality. The horn of the bass speaker of ordinary multimedia speakers is mostly between 3-5 inches. A sound box made of high-performance speakers also means lower transient distortion and better sound quality.
Edit the polarity of this paragraph.
The pin polarities of the speakers are relative, as long as the speakers used in the same room have the same polarity.
When using multiple speakers, it is necessary to distinguish the polarity of each speaker pin for the following reasons: when two speakers are not connected in series or in parallel with the same polarity, the current flowing through the two speakers is in different directions, one flows in from the head of the voice coil and the other flows in from the tail of the voice coil, so that when the paper cone of one speaker vibrates forward, the paper cone of the other speaker vibrates backward, and the vibration phases of the two speaker paper cones are opposite, and part of the energy of air vibration is cancelled. Therefore, when more than one speaker is used in the same room, it is required to be connected in series or in parallel with the same polarity, so that the vibration direction of each speaker cone is consistent.
The positive and negative poles of the two leads have been marked with "+"and "-"symbols on the wiring brackets on the back of some speakers, which can be directly identified.
Audio-visual discrimination method can be used to determine the polarity of speaker pins. Two pins of the two speakers are connected in parallel at will, connected to the output end of the power amplifier, fed with electrical signals, and the two speakers sound at the same time.
Put two speakers together. If the sound is getting louder and louder, it means that the two speakers are connected in parallel with opposite polarities, that is, the positive pole of one speaker is connected in parallel with the negative pole of the other speaker.
The principle of the above identification method is that when two speakers are connected in parallel with opposite polarities, the paper basin of one speaker moves inward and the paper basin of the other speaker moves outward, and the sound pressure between the two speakers decreases, so the sound is low. When the distance between the two speakers is close, the sound pressure between the two speakers is small, so the sound is small.
The method to identify the polarity of speaker pins by using the DC current range of multimeter is: put the multimeter in the minimum DC current range (micro-ampere range), connect the two pins of the speaker at will, and gently and quickly push the paper basin inward with your fingers. At this time, both hands are deflected to the left or right. When the pointer of the watch is deflected to the right (if it is deflected to the left, the red and black bars are connected to each other once), the pin connecting the red bar is positive, and the pin connecting the black bar is negative. Use the same method and polarity adjustment to test other speakers, so that the pin polarity of each speaker is consistent.
The principle that this method can identify the polarity of the speaker pin is that when the paper basin is pressed, the voice coil cuts the magnetic field generated by the permanent magnet due to the movement of the voice coil, and the electromotive force is induced at both ends of the voice coil. Although this electromotive force is very small, the multimeter is in a small current range, and the current generated by the electromotive force flows through the multimeter, and the pointer deflects. Because the deflection direction of the pointer is related to whether the red and black pointers are connected to the head or tail of the voice coil, the polarity of the speaker pin can be determined.
In the process of identifying the polarity of the speaker pin, pay attention to the following two points:
(1) When directly observing the lead frame on the back of the speaker, the positive and negative pins of the speaker produced by the same manufacturer have the same polarity; For speakers produced by different manufacturers, there is no guarantee of consistency, so it is best to identify them by other methods.
(2) In the process of identifying the pin polarity of the speaker with a multimeter, it is not easy to see because the number of turns of the voice coil of the speaker is small and the deflection angle of the hands is small. At this time, the paper basin can be pressed quickly, so that the deflection angle of the watch hand becomes larger. When pressing the paper basin, be careful not to damage it.
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Open circuit fault: the resistance between the two pins is infinite, which is silent in the circuit and there is no noise in the speaker.
Breakage fault of paper basin: this fault can be found by direct inspection, and the speaker with this fault should be replaced.
Poor sound quality fault: this is a soft fault of the speaker. Usually no obvious fault features can be found, but the sound is not pleasant. Speakers with this fault should be replaced.
Under amateur conditions, you can only use audition and multimeter to test speakers.
The audition inspection method is to connect the speaker to the output end of the power amplifier and evaluate its quality subjectively by listening to the sound.
It is also rough to detect the speaker with a multimeter.
Measuring DC resistance: Measure the DC resistance between the two pins of the speaker with R* 1 gear, which should be slightly less than the nameplate speaker impedance under normal circumstances. For example, the resistance measured by an 8 ohm speaker is usually around 7 ohms. The measured resistance is infinite, or much greater than its nominal resistance, indicating that the speaker has been damaged.
Listen to the click: When measuring DC resistance, you should be able to hear the click from the speaker by disconnecting the pin of the watch lever. The louder, the better. Without this sound, the voice coil of the speaker is stuck.
Visual inspection: check whether there is a broken paper basin in the speaker.
Check the magnetism: test the magnetism of the magnet with a screwdriver. The stronger the magnetism, the better.