1) How to choose a speaker?
Loudspeaker is actually an audio electric power signal, which can be heard by transducer (loudspeaker unit) and converted into audible sound with sufficient sound pressure level. In order to choose a good speaker correctly, we must first understand the properties of sound signals, and then ask the speaker to restore audio electrical signals to realistic and natural sounds.
Human voice and all kinds of music are random signals, and their waveforms are very complicated. The frequency range of audible sound can generally reach 20 Hz-20 kHz; The frequency spectrum of the language is about150hz-4khz; The spectrum range of all kinds of music can reach about 40HZ- 18KHZ. The energy distribution of the average spectrum is as follows: bass and mid-bass are the largest, followed by mid-treble, and treble is the smallest (about10/1); The energy of human voice is mainly concentrated in the frequency range of 200HZ-35KHZ. The peak amplitude of these audible random signals is higher than its average value 10- 15DB (even higher). Therefore, in order to reproduce these random signals correctly and ensure beautiful sound quality, speakers must have wide frequency response characteristics, sufficient sound pressure level and large signal dynamic range. We hope to get a large enough sound pressure level with a relatively small signal power input, that is, speakers are required to have high-efficiency sensitivity and convert electric power into sound. In addition, we also require that the speaker system will not be damaged when the input signal is moderately overloaded, that is, it must have high reliability. Another point is that users want to buy good products with "good quality and low price", that is, products with high cost performance. Finally, the support mode, external structure and hoisting mode of the product should be considered.
2) Application of main technical characteristics of loudspeaker system
There are many technical characteristics of speaker system, which are directly related to the timbre effect and usage occasions. In order to make full use of these technical features, users must understand them.
1) Two-way (divided by two) and Three-way (divided by three) speaker system
The frequency spectrum of audio signal is very wide, so it is impossible for a speaker unit to meet the full frequency response of 20HZ-20KHZ signal. Because the general large-caliber speaker unit above 12 inch has good bass characteristics and small distortion, but the performance is poor when the signal exceeds 1.5HZ; 1-2 inch treble unit (treble compression driver) has a good performance in reproducing signals above 3KHZ, but it cannot reproduce midrange and bass signals. So there is a loudspeaker system composed of various frequency response characteristic units. Two-channel speaker system consists of bass (including midrange) and treble (including midrange), and three-channel speaker system consists of bass, midrange and treble.
The two-way loudspeaker system has simple structure and relatively low cost. In order to solve the problem of lacking this midrange frequency, some manufacturers have adopted a compromise method, that is, on the frequency division network, the frequency response characteristics of bass units are moved up and the frequency characteristics of treble units are moved down. Another problem is that the crossover frequency can only be set between 500 Hz and 2 kHz, which is an important part of human speech and music spectrum. Therefore, it will leave a sense of "hollowness" and audible distortion (of course, the slope characteristics of the frequency divider are larger, such as 18DB/ octave, and this defect can be compensated). Because of this, two-way speakers have higher requirements for speaker units. If the unit performance is not good, the sound of the whole speaker system is not smooth enough or the phase distortion is serious.
The characteristics of each unit of the three-way loudspeaker system can be fully utilized, and the two intersections can be selected at the upper and lower edges of the spectrum of the midrange voice and the important part of music, which has no influence on the sound quality. Therefore, the three-channel speaker system reduces the distortion of sound, improves the clarity of sound, improves the performance of the cross band between bass and treble, and increases the power handling capacity of the speaker system. Therefore, it is the best choice for theatrical performances, concert halls and opera house sound reinforcement systems.
2) Sensitivity and maximum sound pressure level (maximum SPL)
Speaker unit is a transducer between electrical signal and sound, which requires that it can be converted into loud sound with relatively small input power, which requires the speaker to have high sound pressure sensitivity. The essence of "sensitivity" is the reflection of "conversion efficiency". Due to the differences in design technology, materials and production technology, the sensitivity of various speaker systems is also very different. Sensitivity refers to the magnitude of sound pressure level measured at the distance of 1 meter in the direction of the speaker axis when the electric power input to the speaker unit is 1 watt. If the sensitivity of the two speakers is 3DB different, to achieve the same sound pressure level output, it is necessary to double the electrical input power, so that the speaker with higher sensitivity can make louder sound.
The input power capacity of the speaker system is generally much larger than 1 watt (generally between 100 watt and 2000 watt), so this maximum allowable electric power can be input in actual use. Under the rated maximum power, the sound pressure level generated at the speaker axis 1 m when the speaker is input is called maximum sound pressure level SPL MAX. For example, a speaker with a sensitivity of 100 dB,1w 1m and a maximum power bearing capacity of 1000W, then splmax =100db+30db =130db, In addition, we are concerned about how much the synthesized sound pressure level of two speakers with the same sound pressure level will increase.
-"The answer is: it will increase by about 3DB outside the radius of twice the indoor reverberation sound field."
This leads to a cost-effective economic accounting problem. For example, a speaker with SPL 1=90DB has a unit price of 5,000 yuan, and another speaker with SPL2=99DB has a unit price of 20,000 yuan. If the system requires a sound pressure level of 99DB, eight speakers with low sound pressure level (8× 5000 = 40,000 yuan) are used, and the other speaker with high sound pressure level only needs 65,438+.
3) Distortion and sound quality
Unfortunately, the speaker factory has no nominal product distortion rate, but it is actually a very important technical parameter. Sound quality is an abstract evaluation, which can't be marked on the file, so we can only do subjective listening test. Usually sensitivity and sound quality are contradictory, and manufacturers need to make an appropriate balance between them. Generally speaking, low-priced products are sensitive and pursue cost performance. High-priced products focus on sound quality. And the highest state is both.
4) "Personality" and "* *"
Here is another relatively abstract and subjective performance evaluation. The audio used for sound reinforcement is different from the HI-FI audio equipment at home, so it must be very compatible, because each venue may perform different types of programs, from opera to rock concerts, or it may only be based on voice signals ... So its audio system must be compatible with different program sources in order to achieve excellent "balance", that is, it cannot be biased towards a certain purpose. HI-FI audio equipment at home only needs to take care of the taste of one person or a very small number of people, allowing the "personality" of its products to exist. However, as a professional sound reinforcement system equipment, this "personality" will become a "limitation" or "defect". Professional sound reinforcement materials need to serve a large group of people, and the program content often changes. "* * *" is a basic requirement with strong compatibility. Different kinds of programs should have "general" performance. In addition, professional sound reinforcement equipment must restore the sound source, and cannot be "exaggerated", "exaggerated" or "loyal". This is * * * or * * *.
5) Directional characteristics of loudspeaker system
The sound emitted by the loudspeaker is usually non-directional in the low frequency band (below 200 Hz) and propagates uniformly in all directions. In the high frequency band, sound propagation shows strong directivity, which is exactly what we want to apply in system design. Excellent directional characteristics can concentrate the energy of sound waves in the audience area when the venue is arranged, and avoid the interference between the strong reflection surface of sound waves and the sound field. For example, the flashlight on the market is easy to distinguish. The price difference between an ordinary flashlight and a flashlight with spotlight function can be dozens of times. Even if the power of a general flashlight is the same as that of a spotlight flashlight, the light cannot be projected very far and the projected area cannot be controlled. The high-pitched part of the speaker is like the light of a flashlight. If you only need sound, any grade of speakers can do it, which means that any ordinary flashlight can also illuminate. However, as a large-scale project, it is necessary to effectively control the sound field distribution and consider the projection distance. The directivity is good or bad enough to affect the success or failure of the project, so it is necessary to choose a speaker with excellent directivity. The directivity of the loudspeaker makes the off-axis sound pressure level gradually decrease with the increase of deflection angle; At the same time, the sound pressure level decreases with the increase of sound wave propagation distance and is inversely proportional to the square of the distance. If these two kinds of attenuation are properly selected, they can compensate each other and make the sound field more uniform. Large-scale projects need to cover a relatively wide area, and a single speaker is usually not enough. It is necessary to combine multiple speakers into a speaker group (array). In the array loudspeaker system, the constant pointing characteristic can make the sound waves in the middle and high frequency bands between loudspeakers not interfere with each other. Using a pair of speakers with the above-mentioned constant pointing characteristics to form a figure-eight display can cover twice as much as a single speaker. Otherwise, the sound has interfered with each other in front of the speaker, which seriously affects the uniformity of the sound field and the clarity of the sound.
6) Power handling capacity of speaker system
The power handling capacity of the loudspeaker system (or the rated power of the loudspeaker) is an important technical parameter, which represents the power input capacity of the loudspeaker to withstand long-term continuous and safe work. In order to understand the power handling capacity of the loudspeaker, we must first understand how the loudspeaker exciter is damaged. There are two types of actuator damage: one is voice coil overheating damage (voice coil burning, overheating deformation, inter-coil breakdown, etc.). ), the other is that the displacement of the driver diaphragm exceeds the limit value, which makes the conical diaphragm and diaphragm of the speaker. The sound signal is not a pure sine wave signal, but a random signal. These random signals can be expressed by three parameters: RMS (root mean square) is the measurement result of a sinusoidal signal with the same peak amplitude as the signal, which is close to the average value and basically represents the heating energy of the signal.
The peak value is the maximum level reached by the signal. For sine wave, the peak level is 3DB higher than the rms level. For music signals, the peak level can exceed the effective value 10- 15DB. Peak value is very important when evaluating the displacement ability of loudspeaker. Peak factor, used to explain the ratio of peak level to root mean square level. According to AES2- 1984, the peak coefficient of pink noise source is 6DB, that is, the peak voltage is four times the root mean square voltage. The power handling capacity of the loudspeaker is a technical parameter measured under the condition that the permanent change of its electrical and mechanical properties is not more than 10% after the pink noise signal processed by (AES2- 1984) is continuously added for 2 hours.
7) The sound pressure level drops after loading (heating) (also called power compression)
The nominal power in all product manuals is determined by each manufacturer, which is the best value of the speaker under the test signal and conditions selected by the manufacturer. When the speaker enters the working state (for example, after 20 seconds of full charge), after the voice coil and magnet are heated, the original characteristics of the unit before heating are changed due to their performance degradation, and the actual sound pressure output will decrease at this time. When the temperature of traditional speakers, such as voice coils, rises from 60℃ to 80℃, the rated sound pressure level usually has a tolerance of 3DB. For example, the voice coil has excellent heat dissipation. When the temperature reaches 100℃, the actual sound pressure drop can reach 6 to 8DB, which is quite amazing. As mentioned above, if the sound pressure level of the speaker is doubled, it will only increase by 3DB. If the sound pressure level of speakers is reduced by 6DB, it must be increased from one speaker to four speakers to make up for such a large reduction. Unfortunately, the audio industry has no habit of nominally reducing the sound pressure level, and users can only choose the best brand by themselves. In order to improve this drop in sound pressure level, it is necessary to better improve the heat dissipation design of the speaker unit.
8) Impedance of speaker unit
The impedance of the speaker unit includes inductance, capacitance and resistance. Inductance and capacitance vary with frequency. Although the impedances in a speaker system (such as 8 ohms and 4 ohms) are nominal values, the values will vary with the frequency. If the impedance changes too much, it will affect the stability of the whole sound system. ***L The latest DCD dual-coil differential drive design is to change the impedance into "pure resistance", which is not affected by the frequency change and makes the whole sound system work stably.
3) How to improve the reliability of the loudspeaker system
In daily life, even if the power of the power amplifier matches the power of the speaker system, the speaker unit will be damaged. The reason is:
1. The power amplifier is improperly operated and the output power is too high.
2. At the climax of the performance, the atmosphere in the venue is warm and the sound pressure needs to be increased. When the signal is increased, the input signal of the microphone is too large, which leads to the overload and clipping of the power amplifier, and the distorted waveform produces a lot of harmonics, which damages the high-pitched unit.
3. The microphone produces strong acoustic feedback howling, and the power amplifier is strongly overloaded, which damages the speaker system. For this reason, modern new loudspeaker systems adopt a variety of protective measures, which can be divided into two categories:
(1) Improve the heat dissipation of the speaker unit so that it will not be damaged by overheating when overloaded.
(2) Install a limiter protection device in the speaker box. When the driving power and peak level exceed the rated value of the speaker, the limiter will use a nonlinear resistor (bulb) to prevent the voice coil from exceeding the power level. These measures improve the anti-overload ability of the speaker, but also affect the dynamic range of the sound, making the range not wide enough and the timbre feeling fuzzy and dim. Therefore, the best way is to take measures on the power amplifier, so that its output does not appear clipping, power overload and other problems.
4) What new technical measures have been taken for the ***L speaker system?
In recent years, American ***L Company has taken many effective new technical measures in design and production to continuously improve the performance of speaker system.
Treble unit:
The patented technology of three-dimensional diamond pattern blank holder for titanium alloy diaphragm is adopted, which is as light as tissue paper and harder than steel, and the thickness is only 0.00 1 inch. This technology not only makes the treble clearer and brighter, but also can withstand greater impact.
The voice coil conductor is made of aluminum alloy conductor with special square section and insulating paint with special formula, which makes the voice coil light and compact and improves the power capacity and sound pressure sensitivity.
Magnetic fluid is used to improve the heat dissipation condition of voice coil and enhance the anti-overload ability.
A new KAPTON material is used as voice coil bracket. The thermal conductivity of this material is twice that of conventional materials, and it can withstand higher temperatures, ensuring that the voice coil can still work normally at high temperatures.
"SONICGUARD" is a breakthrough invention of ***L, which prevents the high-pitched unit from being damaged due to sudden high-power peak signal or long-term overload. The difference between SONICGUARD and general amplitude limiting protection technology is that it can let many signals in music that are very dynamic and have insufficient energy to burn the voice coil pass. It will automatically shunt and attenuate overload energy and destructive peak signals to a safe level. This process is carried out automatically in mute state, and the purpose of protecting the speaker unit is achieved without sacrificing the sound quality (sense of music and clarity).
Alto/alto unit:
In order to cooperate with the new speaker, ***L specially developed a super-large compression driver such as 2447, which has a flat high-frequency response to 18KHZ, improved the midrange sound quality, and made the sound of the whole middle and high section clearer and brighter without being harsh. The performance of the two-channel loudspeaker system composed of this unit can be comparable to that of the three-channel system.
Bass unit:
In the transducers designed by SVG and VGC for heat dissipation, the bass unit often has to bear a lot of power continuously, and only a small part of movie energy is converted into acoustic energy, and most of it becomes harmful heat energy. After the voice coil heats up, the output sound pressure level first decreases, then the sound distortion increases, and finally the voice coil will burn out. In order to improve the output effectively, the heat dissipation condition of voice coil must be improved. ***L patented SVG and VGC designs have made multiple air slots in the throat of the driver, and air convection is formed by the vibration of the diaphragm, which can effectively dissipate heat.
The oversized 4-inch voice coil and diaphragm not only improve the power capacity, but also expand the frequency response and improve the distortion.
Adopt high-performance magnetic steel material-magnetic steel. Its magnetic field strength is more than 10 times higher than that of traditional magnetic materials. High-efficiency magnetic steel improves the sound pressure sensitivity, dynamic range and weight of the loudspeaker.
High power, low loss and high quality frequency divider
High-power and high-quality frequency divider is also a key component that directly affects timbre. The frequency divider must be accurately matched with the characteristics of the loudspeaker unit, so as to obtain flat characteristics, correct frequency division points, less nonlinear distortion and good sound quality. ***L Successfully increased the original frequency division slope from 1.2 dB/ octave to 1.8 dB/ octave, which made the timbre clearer and minimized the mutual interference between units. * * * The frequency divider used in L speaker has made great efforts in design, material selection and manufacture, and adopted special four-lead resistor, ultra-low resistance inductor and precise low-loss styrene capacitor.
New concept of high-tech products-EON series active speakers;
EON series active speakers adopt brand-new conceptual design and advanced production technology, which makes them the most popular, cheapest and multifunctional portable products.
EON series speakers use high-performance magnetic materials, such as magnetic steel, aluminum instead of steel basin frame, plastic instead of wood box. The special and sturdy integrated box coupling plate structure greatly reduces the weight and is convenient to carry and fix.
EON's treble and bass units all adopt the above-mentioned new technical measures, and also adopt the differential double voice coil technology in reverse series for the first time, so that the impedance of the speaker presents the nature of "pure resistance", so the frequency response is particularly wide and flat, and the timbre is extremely clear and beautiful.
EON's built-in power amplifier skillfully uses the airflow generated by the echo hole of the speaker when the diaphragm vibrates to bring heat outside the box, so it can be used continuously for a long time in harsh outdoor environment. 300-hour full-load test -* * * L guarantees your quality.
According to the American electrical standard AES2- 1984, as long as the speaker unit passes the 2-hour full-power load test, ***L will automatically raise this test standard to 300 hours, which is the guarantee of ***L to the user's quality.
5) What output power amplifier should the speaker system be equipped with?
The loudspeaker system needs to reproduce various music programs with high quality, so according to the nature of the music signal, its peak factor is about 10- 15DB. From the point of view of ensuring sound quality, the power amplifier should not have any clipping in this dynamic range, that is, the maximum output power of the power amplifier should be 5-8 times of the rated power of the speaker. Although the sound quality of this power configuration is good, the investment will be large, so it is average.
The range of 1-2 times may be too vague, so we can give you a more specific experience.
1. In some projects with low requirements and limited investment, the power of the power amplifier is at least equivalent to the rated power of the speaker. But be very careful to keep the sound undistorted. Too small a power configuration does not seem to damage the speaker unit, but this is not the case. Too low power is easy to overload and clip, producing a lot of harmonics and burning out the high-pitched unit.
2. General engineering suggests that the power of the power amplifier is 1.5 times. The bass part is preferably 1.5 times, so as to get enough strength.
3. Extremely demanding venues, such as studio monitoring and concert halls. Ideally, it is twice as large as a speaker. (This is consistent with one of the recommended values of supporting standards formulated by IEC).
There is no hard standard for the design of power amplifier, which depends entirely on the investment budget and the requirements for sound quality.
Fixed installed audio equipment
For half a century, ***L has spread all over the world, serving hundreds of millions of users. There are too many famous projects to record. ***L has become a technical standard and model reference for designers and engineers.