Understanding of speakers and judging fake and inferior

1. Cabinet design:

A speaker is a device that restores an electrical signal to a sound signal, and the authenticity of the sound will be used as an important criterion for evaluating the performance of the speaker. The speaker is composed of several main parts such as the cabinet, the speaker unit, the power supply part and the signal amplification. In addition to some special flat panel, horn, labyrinth and other speakers, we can divide ordinary speakers into two types: inverted and closed:

① Closed speaker, which is to install a speaker on a closed box, that is, to completely isolate the sound waves inside and outside the box, which is equivalent to listening to the side of an infinite baffle. For a closed box, the sound waves in the box are not used, but in order to reduce the interference of the useless sound waves (standing waves) in the box on the vibration of the speaker, it is generally necessary to put some sound damping materials with higher efficiency in the box. Such as porous cotton. These damping materials can not only absorb sound waves, but also reduce the speed at which air molecules propagate sound, which is equivalent to increasing the volume of the box and reducing the impedance peak at the resonance frequency. Therefore, the efficiency of the closed box is low, and its sensitivity is about 5dB lower than that of the inverted box. Fortunately, the airtight box is powerful in low frequencies, good in transients, fast in response, and clear in low frequencies. It is effective in listening to classical music and chamber music, but the depth of the dive is limited and the low frequency is insufficient.

②Inverted phase speaker, which works according to the principle of Helmholtz resonator. The difference between it and a closed speaker is that a cylindrical inverted hole is installed on the front of the speaker to communicate with the air inside and outside the box. It has a higher power bearing capacity and lower distortion and a sense of volume than a closed speaker. High enough and high sensitivity, it can be more versatile in various occasions. Because the sound wave on the back of the speaker can also be emitted from the phase guide hole, its efficiency is also higher than that of a closed box. Not only that, but the same loudspeaker installed in a suitable inverter box will get 3dB higher low-frequency sound pressure than in a closed box of the same volume, which is more conducive to the performance of the low-frequency part. The details are that the inverter box uses the air in the speaker and the vibration of the air column in the inverter hole, and relies on the reflection of the back panel of the speaker to invert the sound wave behind the speaker by 180 degrees, and then the inverted hole Part of the sound wave is transmitted so that this part of the sound wave is in phase with the sound wave directly emitted by the speaker, which increases the low-frequency radiation energy, so this is also an important reason why the inverter box is now widely popular. The damping requirement of the inverter box is actually higher than that of a closed box. It is necessary to ensure that the box body cannot have unconventional sound leakage, such as loose screws, popping air leakage in the gap between the screw holes of the speaker or the board. The cross-sectional area of the inverted box hole is equal to or slightly smaller than the effective area of the vibrating cone. If the opening diameter is too small, the air flow rate in the inverted tube will increase, which increases the friction loss. The speaker can be composed of two or more speakers, so it can be divided into two-way and multi-frequency. Most multimedia speakers are two-way, which is also found in terms of manufacturing cost and performance. A point of balance.

2. Shell:

Common speakers are mainly made of wood or plastic (some speakers are also poured and filled with cement, steel, sand, etc.). Wooden speakers are made of composite medium and high-density boards, and the thickness should be more than 10mm. Compared with plastic speakers, it has better anti-resonance performance, speakers can withstand greater power, and the volume is not limited by molds; the cost of plastic speakers is relatively low, and it is a one-time molded product of molds. It can be designed in terms of shape. Very rich but limited in size, relatively small, and the tolerable maximum output power is also relatively small, only suitable for the range of multimedia speakers. Inferior speakers are mainly because the density of the MDF is not high enough, the plate is very thin, or the texture of the plastic is crisp, sand holes, easy to crack, etc.

3. Power supply part:

The circuit in the speaker is a low-voltage circuit, so you first need a transformer that converts high voltage to low voltage, then use two or four diodes to convert AC to DC, and then use large and small capacitors to filter the voltage to make the output The voltage tends to be flat (the voltage regulator tube is generally unnecessary in ordinary speakers). To be honest, these are the parts that are not noticed very much. In fact, their importance to the speakers is no less than the importance of the host power supply to your computer.

The transformer is generally fixed at the bottom of the main speaker (this is also the reason for the weight of the main speaker). The requirement for it is to have sufficient power output. Inferior products often cut corners here. Taking into account some factors of loss and efficiency, it can be calculated that if the rated power of the transformer is 100W, the power of the power amplifier chip that it can actually drive smoothly should be below 45-40W, so it can be verified by calculating the power relationship between the speaker transformer and the power amplifier. Whether the actual rated power of the speaker can reach the nominal value. The rectifier part and the filter capacitor are both on the circuit board. The large filter capacitor (thousands of micro waves) should use electrolytic capacitors and the larger the better. You can use a large capacitor or two medium-capacity capacitors in parallel to achieve filtering. The following small capacitor (less than a few fractions of microfarads) is to make up for the lack of high-frequency filtering of the large filter capacitor. The rectification part is generally not a big problem, but in order to reduce costs, the capacity of the filter capacitors of inferior speakers is obviously insufficient, and some are even less than 2000 microfarads, and small capacitors are likely to be ignored by them.

 4. Power amplification part:

This part is composed of the pre-amplifier and the post-amplifier. The pre-amplifier only plays the role of voltage amplification. In order to prepare for power amplification, it pre-amplifies the voltage amplitude of the input signal above the minimum value required by the power amplification. In addition to the frequency range and distortion, the requirements for it are The important thing is that the magnification is sufficient. For the power amplifier chip, it can be called the core of the speaker, and the key is its rated power. According to the standard, the rated power of the marked speakers should not exceed the typical value of the power amplifier chip, and if there is a higher part, it is the "frugality" of inferior speakers.

5. Circuit part of special sound effects and functions:

This part is not available in all speakers. A speaker may have the same or a few of them, or it may not be the same. This includes the digital-to-analog conversion circuit part of the USB speaker, the digital input and digital adjustment part of the digital speaker, the three-dimensional sound field processing chip (such as: SRS, APX, Spatializer3D, etc.), active electromechanical servo technology circuit and BBE high-definition plateau sound weight Put system technology circuit and so on. From a technical level, small workshops cannot make digital speakers, so manufacturers who can make digital speakers have a certain level of technology and should be trusted. In terms of three-dimensional sound field processing technology, the chips used are all foreign ready-made chips, which are just a matter of circuit interface and location. What I want to say here is that some low-end speakers also have a 3D sound field function. Their 3D effect is not achieved by the chip, but by a very simple feedback circuit. The effect can be imagined.

6. Speaker unit:

General wooden speakers and better plastic speakers use two-way frequency technology, that is, high and mid-range speakers are used to achieve sound playback in the entire frequency range; and some are in X.1 (X=2, 4 or 5). ) The plastic speakers used as surround speakers above use full-band speakers, that is, one speaker is used to achieve sound playback in the entire sound range. Since the speakers used in the multimedia field must have magnetic discharge, dual magnetic circuits are used in the design of the speakers, and the method of adding a magnetic cover behind the speakers is used to avoid the leakage of magnetic lines of force. In order to save costs, the speakers of counterfeit speakers are likely to be non-magnetic!

7. About the subwoofer:

For the subwoofer, in order to ensure that the performance of the speaker requires a strict enclosure, a three-chamber design should be adopted, that is, there are two layers of cavities behind the speaker. There is also a two-cavity design with dual speakers, that is, there is only one cavity behind the speaker, and one cavity in front of the speaker is two cavities. Take the speaker products of Chuangtong as an example. The subwoofer of their Sound Works series of ordinary products adopts a two-chamber design, and the subwoofer of their Sound Works series of good products DTT2500 (5.1) has a three-chamber design, which can be seen in the subwoofer. There are also different grades.