The sound is actually an audible sound that passes the audio electric power signal in the audible range through the transducer (speaker unit) and converts it into a sound pressure level. In order to correctly select the speaker, you must first understand the properties of the sound signal, and then ask the speaker to restore the audio signal to a realistic and natural sound "as is". The speaker should be able to correctly reproduce these random signals to ensure playback. The sound quality is beautiful, the speakers must have a wide frequency response, sufficient sound pressure level and large signal dynamic range. We hope to achieve a sufficiently large sound pressure level with a relatively small signal power input, which requires the speaker to have a high efficiency of converting electrical power into acoustic sensitivity.
We also require the speaker system to be protected from damage if the input signal is overloaded properly, that is, to have higher reliability. Another point is that users hope to buy a good product with good quality and low price, that is, a product with high performance and price ratio. Finally, we must consider the supporting methods, shape structure and lifting method of the product. Speaker systems have a number of technical features that are directly related to the effects of the sound and the use of the application. In order to use these technical features, users must understand them. Speaker system two (two-way) and three-way (three-way audio signal spectrum range is very wide, the 20Hz-20KHz signal to use a speaker unit can not meet the entire frequency response; because the general 12 inch The above large-caliber speaker unit has good bass characteristics and little distortion, but its performance is very poor when the signal exceeds 1.5Hz; the 1-2 inch tweeter unit (treble compression driver) reproduces the signal performance above 3KHz. Very good, but can't replay the midrange and bass signals. So there is a speaker system consisting of various frequency response characteristics, consisting of two units: bass (including mid-bass) and treble (including middle and high-pitched). For the two-way speaker system, the three-channel system consists of three units: bass, midrange and treble. The two-way speaker system has a simple structure and relatively low cost. In order to solve the missing mid-range audio rate, some manufacturers use it. A compromise method is to move the frequency response characteristic of the woofer upward on the crossover network to move the frequency characteristics of the tweeter down. Another problem is the crossover frequency. It can be set between 500Hz and 2KHz, and this area is an important part of the vocal and music spectrum. Therefore, it will leave a “cavity†and audible distortion in the auditory (of course, the slope characteristics of the crossover are large. Some, for example, 18dB/octave, this defect can get some compensation.) Because of this, the requirements of the two-channel speaker for the speaker unit are relatively high. If the performance of the unit is not good, the sound of the entire speaker system is not smooth enough. Or there is severe phase distortion. The characteristics of each unit of the three-way speaker system can be compromised, and their respective strengths can be fully utilized. The two crossover intersections can be selected on the important part of the midrange vocal and music spectrum. At the lower edge, there is no effect on the sound quality, so the three-way speaker system reduces the distortion of the sound, improves the clarity of the sound, improves the performance of the cross band between the bass and the treble, and increases the power handling capability of the speaker system. The best choice for theatrical performances, concert halls and opera sound reinforcement systems.
The speaker unit is a transducer between the electrical signal and the sound, which is required to be replaced with a very loud sound with a relatively small input power, which requires the speaker to have a higher sound pressure sensitivity. "Sensitivity" is essentially a manifestation of "conversion efficiency." Various types of speaker systems vary greatly in sensitivity due to differences in design techniques, materials selected, and production processes. Sensitivity refers to the amount of sound pressure level measured by inputting 1 watt of electric power from the speaker unit and 1 meter away from the axis of the speaker. If the sensitivity of the two speakers differs by 3 dB, to achieve the same large sound pressure level output, it is necessary to increase the electric input power by a factor of two, so that the speaker with higher sensitivity can emit a larger one.
Personality and commonality: Another relatively abstract and subjective performance evaluation is introduced here. The sound for sound reinforcement is different from the HI-FI audio equipment in the home. It must be very compatible, because each venue may perform different types of programs, from opera to rock concerts. The report will be ... so the sound system must be compatible with different program sources, to achieve the "average" excellence, that is, can not be biased on a specific use. The HI-FI audio equipment in the home only needs to take care of the taste of one person or a small group of people. The "personality" of the product is allowed. However, as a professional sound reinforcement system equipment, this "personality" will become "limited" or "defective". Professional sound reinforcement equipment needs to serve a large group of people. The content of the program is often changed. The "commonness" is the basic requirement, the compatibility is strong, and the programs of different natures must have an "average" performance. In addition, professional sound reinforcement equipment must be "no rendering", "no exaggeration", "faithful" to restore the sound source. This is "commonity" or "commonness." The directional characteristics of the speaker system spread evenly in all directions. However, in the high frequency band, the sound transmission has a strong directionality. This directional characteristic (various types of speakers are different) is exactly what we should apply in system design. The excellent constant pointing characteristic can concentrate the energy of the sound wave into the audience area when the scene is arranged, avoiding the strong reflection surface of the sound wave and the sound field mutually interfering with each other. Try an easy-to-understand example. The flashlight on the market, an ordinary flashlight and a flashlight with a concentrating function, may vary by a factor of ten. A typical flashlight has the same power as a spotlight flashlight, but the light cannot be projected far away and the projected area cannot be controlled. The high-pitched portion of the speaker is quite similar to the light from a flashlight. If you only need a sound, what grades of speakers can be obtained, it is equal to any ordinary flashlight can also be illuminated. However, as a large-scale project, it is necessary to effectively control the sound field distribution and consider the distance that can be projected. The pros and cons of directivity can affect the success or failure of the project, and must choose a speaker with excellent directivity. The sound emitted by the speaker is usually non-directional in the low frequency band (below 200Hz), and the directivity characteristic of the speaker makes the off-axis sound pressure level gradually decrease with the increase of the declination angle; As the distance of the sound wave propagation increases, it is inversely proportional to the square of the distance. In the audience zone with different distances and directions from the speaker, if the two attenuations are properly selected, the two attenuations can be compensated for each other, thereby making the sound field more uniform. . Large projects need to cover a relatively large area, and a single speaker is usually not enough to cope with it. It is necessary to combine multiple speakers into a group of speakers (array). In the array speaker system, the constant pointing characteristic allows the sound waves in the middle and high frequency bands between the speakers to not interfere with each other between the speakers. A pair of speakers with the above constant pointing characteristics can be used to form a splayed shape, which can cover twice the size of a single speaker. Otherwise, the sound has interfered with each other in front of the speaker, seriously affecting the uniformity of the sound field and the clarity of the sound. The power handling capability of the speaker system and the power handling capability of the speaker system (or the rated power of the speaker) are an important technical parameter. It represents the power input capability of the speaker to withstand long-term continuous safe operation. To understand the power handling capability of the speaker, you must first understand how the speaker driver is damaged. There are two modes of damage to the driver: one is the voice coil overheating damage (the voice coil is burned, Another type of thermal displacement, inter-turn breakdown, etc.) Low frequency signal. The sound signal is not a pure sine wave signal, but a random one. These random signals can be expressed by three parameters: the effective value (RMS), also called the rms value, is the sinusoidal signal of the signal peak amplitude. A measurement that is close to the average and basically represents the heating energy of the signal. The peak value (PEAK) is the maximum level reached by the signal. For a sine wave, the peak level is greater than the effective value level by 3 dB. For music signals, the peak level exceeds the effective value by 10-15 dB. The peak value is important when the speaker's displacement capability. The crest factor is used to account for the ratio of the peak level to the rms level. For a pink noise source according to AES2-1984, the crest factor is 6 dB, ie the peak voltage is 4 times the rms voltage. The power handling capability of the speaker is measured by the pink noise signal processed after (AES2-1984) for 2 hours, and the permanent change of electrical and mechanical properties is not more than 10%. Sound pressure level drop after heating) (also known as power compression) The nominal power on all product specifications is custom-made by each manufacturer and is the optimum value of the speaker under the test signals and conditions selected by the manufacturer. When the speaker enters the working state (for example, equal to or greater than 20 seconds of full power), the voice coil and the magnet are heated and the temperature rises. Because of their performance degradation, the original characteristics of the unit before heating are changed. At this time, the actual sound pressure output will be cut back. Conventional speakers, such as voice coil temperature rise 60 ° C -80 ° C, common rated sound pressure level drop of 3dB for tolerance, such as voice coil heat dissipation, and temperature up to 100 ° C, the actual sound pressure drop can reach 6dB-8dB, this It is quite amazingly falling. As mentioned in the previous question, the doubled speaker only increases the sound pressure level by 3dB. If the sound pressure level of the speaker drops by 6dB, to compensate for such a large sound pressure level drop, it must be increased from one original speaker to four. It is a pity that the audio industry does not have the habit of claiming such a drop in sound pressure level. Users can only try their own choices for various brands. To improve the drop in sound pressure level, the heat dissipation of the speaker unit must be better improved. The impedance of the speaker unit's impedance speaker unit includes inductance, capacitance and resistance. Inductance and capacitance vary with frequency. Although an impedance is nominally in the speaker system, such as 8 ohms, 4 ohms, this value will change as the frequency changes.
How to improve the reliability of the speaker system: In daily life, even if the power matching of the amplifier and the speaker system is equivalent, the speaker unit may be damaged. The reasons are as follows: 1. Improper operation, the power output of the power amplifier is too large; 2. When the performance reaches a climax, the atmosphere in the field is warm, and the sound pressure needs to be increased. When the signal is increased, the input signal of the microphone is too large, causing the power amplifier to be overloaded and clipped. The distorted waveform generates a large number of harmonics, damaging the tweeter; 3. The microphone produces a strong acoustic feedback howling, the amplifier is strongly overloaded, and the speaker system is damaged. To this end, the modern new speaker system adopts a variety of protective measures, which can be divided into two categories: (1) Improve the heat dissipation of the speaker unit so that it does not overheat damage when overloaded; (2) Install in the speaker Limiter protection device, when the drive power and peak level exceed the rated value of the speaker, the limiter blocks the voice coil with a non-linear resistor (bulb). These measures improve the speaker's ability to resist overload, but also affect the dynamic range of the sound, making the range not wide enough, and the tone is blurry and dim. Therefore, the best way is to take measures on the amplifier so that its output does not cause clipping and power overload.
The speaker system needs to be equipped with a large output power amplifier: the speaker system needs to reproduce various music programs with high quality, then according to the attribute of the music signal, the peak factor is about 10-15dB. From the perspective of ensuring the sound quality, the power amplifier should be There is no limiting in this dynamic range, that is, the maximum output power of the amplifier should be 5-8 times of the rated power of the speaker. Although the power quality of this power configuration is very good, his investment will be very large, so this will generally be The power ratio is set at 1-2 times the rated power of the speaker unit.
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