A speaker is a device that restores an electrical signal to a sound signal. Restoring authenticity is an important criterion for evaluating the performance of a speaker. Active speakers are speaker systems with power amplifiers (ie amplifiers). The power amplifier and the speaker sounding system are integrated into one body, and can be directly matched with a general sound source (such as a Walkman, a CD player, a DVD player, a video recorder, etc.) to form a complete sound combination. With active speakers, there is no need to purchase a power amplifier, no longer a reasonable choice of power amplifiers, speakers, easy to operate, its high performance and price ratio, generally accepted by the working class.
According to the principle of sound generation and internal structure, the speakers can be divided into inverted type, closed type, flat type, horn type, labyrinth and other types, the most important forms of which are closed and inverted. Closed speakers are equipped with speakers on a closed box, which is relatively inefficient. The inverted speaker is different from the circular inverting hole on the front or rear panel. It works according to the principle of the Helmholtz resonator. It has the advantages of high sensitivity, high power capability and wide dynamic range. Because the sound waves on the back of the speaker are also released from the phase guiding holes, the efficiency is also higher than that of the closed box. Moreover, the same speaker installed in a suitable inverter box will be 3dB higher than the low-frequency sound pressure obtained in the same volume of the closed box, which is beneficial to the performance of the low-frequency part, so this is also a wide range of inverter boxes. An important reason for the popularity.
Some features of active speakers are anti-magnetic: the magnetic field of the speaker speakers can seriously interfere with the screens of TVs and computer monitors, and the screen distortion and large color distortion, which is called "magnetization." In order to avoid the damage of the display without the anti-magnetic speaker, the speaker should have anti-magnetic effect, even if it is close to the TV and the display will not interfere with the screen, the method is very simple, that is, the use of "anti-magnetic" speaker. Usually the price of anti-magnetic speakers is much higher than that of ordinary speakers.
Full-band speaker: This is a surround speaker for multimedia active speakers. Because X.1 channel reduces cost, the discrete speaker (requires two speakers to divide) is simplified into a full-range speaker, which can basically show the entire range of the range. Well done full-band speakers are better than cheap coaxial speakers. However, it is difficult for the honest speaker to completely cover the audible frequency range of the human ear, and it is necessary to share the sound reproduction of the entire range by a plurality of speakers. And through the frequency divider circuit to solve this problem, so the active speakers with dual-frequency high-bass design for better playback.
Flat-panel speakers: Recently, the speaker design of the flat-panel speaker is very popular. It is probably that you have a beautiful appearance and can embed photos, which is cool! The advantage of the flat-panel speaker is that the uniformity and directivity of the sound are good, but the structure is limited, the sound range is narrow, and the low-frequency sound cannot be expressed, so it is generally used with a subwoofer. It is recommended that friends who have high sound requirements do not purchase flat-panel speakers.
USB speaker: It is the speaker that directly inputs the digital audio signal from the USB port on the motherboard into the speaker, and then processes the signal through the built-in D/A conversion circuit of the speaker. On the surface, the advantage of using USB speakers is that the sound quality can be improved, because the digital signal will not be interfered during transmission, and the signal purity is good, but the core of the USB speaker is the D/A conversion circuit, and the conversion accuracy is on the performance of the speaker. The impact is very large. Currently, the popular D/A conversion circuits on the market are 16bit and 20bit. Of course, the latter is better. This data is much worse than the enthusiast amplifier (because it is impossible to use expensive modules). The disadvantage of USB speakers is that CPU usage is high, and older motherboards do not support USB. Buying a USB speaker can not buy a sound card, but this will not enable EAX, hard-wave table and other functions that require hardware. Foreign famous brand HiFi boxes basically have no USB design, so friends who have high requirements on sound quality don't have to consider USB speakers.
2, power <br> speaker audio quality and power are not directly related. The power determines the maximum sound intensity that the speaker can emit. It feels like how loud the sound from the speaker can be. According to international standards, power is marked in two ways: rated power (RMS: sine wave rms) and instantaneous peak power (PMPO power). The former refers to driving an 8Ω speaker within the rated range to specify the waveform continuous analog signal, the maximum electric power of the speaker without any damage after a certain interval and repeated a certain number of times; the latter refers to the maximum power that the speaker can withstand for a short time . The US Federal Trade Commission set the standard for power calibration in 1974: driving an 8Ω speaker load with two channels, and measuring the effective wattage when the harmonic distortion is less than 1% in the range of 20 to 20000 Hz, which is the amplifier's Output power, the indicated power is the rated output power. Usually, in order to cater to the consumer psychology, the merchants mark the instantaneous (peak) power, which is about 8 times of the rated power. Imagine the same TDA1521 power amplifier chip with PHILIPS (maximum rated power 30W, THD=10%), and some products are nominally 360W, even 480WP.MPO, is this possible? Does it make sense? So buy multimedia The speaker should be based on the rated power. The power of the speaker is mainly determined by the power of the power amplifier chip and the power of the power transformer. Considering other factors, it can be calculated that if the rated power of the transformer is 100W, the power of the power amplifier chip that can actually be driven smoothly should be below 45W. Therefore, by counting the power relationship between the speaker transformer and the power amplifier, it is also possible to verify whether the actual rated power of the speaker can reach the nominal value. The power of the speaker is not the bigger the better, the application is the best. For the average household user's room of 20 square meters, the true 60W power (the effective output power of the speaker is 30W×2) is enough, but The larger the reserve power of the power amplifier, the better, preferably more than twice the actual output power. For example, if the output of the speaker is 30W, the power of the amplifier is preferably greater than 60W. For the HiFi system, the power of the amplifier that drives the speaker is very large.
3. Frequency range and frequency response <br> The former refers to the range between the lowest effective playback frequency and the highest effective playback frequency that the sound system can reproduce; the latter refers to the connection of an audio signal output with a constant voltage to the system. The sound pressure generated by the speaker increases or decreases with frequency, and the phase changes with frequency. The relationship between the sound pressure and the phase and the frequency (variation) is called the frequency response. Unit decibel (Db).
The frequency characteristics of the sound system are often described by the ordinate of the decibel scale representing the power and the frequency response curve of the frequency represented by the abscissa of the logarithmic scale. When the sound power is 3 dB lower than the normal power, this power point is called the high frequency cutoff point and the low frequency cutoff point of the frequency response. The frequency between the high-frequency cut-off point and the low-frequency cut-off point is the frequency response of the device; the curves of sound pressure and phase lag with frequency are called “amplitude-frequency characteristics†and “phase-frequency characteristicsâ€, respectively. characteristic". This is an important indicator to check the performance of the speaker. It has a direct relationship with the performance and price of the speaker. The smaller the decibel value, the flatter the frequency response curve, the smaller the distortion and the higher the performance. Such as: a speaker frequency response is 60Hz ~ 18kHz +/- 3dB. These two concepts are sometimes indistinguishable and are called frequency response.
In theory, a frequency response of 20 to 20000 Hz is sufficient. Sounds below 20 Hz, although not heard, but other human sensory organs can be perceived, that is, the so-called bass strength can be felt, so in order to perfectly play various instruments and language signals, the amplifier must achieve high fidelity goals. The harmonics of the tones are reproduced. Therefore, the frequency band of the amplifier should be extended, the lower limit should be extended below 20 Hz, and the upper limit should be increased to above 20,000 Hz. The representation of the frequency response of the signal source (receiver, recording deck, and CD player) is different. For example, the frequency response of the FM stereo broadcast specified by the European Broadcasting Union is 10/-2dB when the temperature is 40 to 15000 Hz. The minimum frequency response specified by the International Electrotechnical Commission for the recording studio is 10/-2.5/4 in the case of 40 to 12500 Hz. 5dB (common band), the actual achievable indicators are significantly higher than this value. The upper limit of the frequency response of the CD player is 20000 Hz, and the low frequency end can be made very low, only a few Hertz, which is one of the reasons for the good sound quality of the CD player.
However, the harmonic components that make up the sound are very complicated. The wider the frequency range, the better the sound is, but this is basically correct for medium and low-end multimedia speakers. In the labeled frequency response, we usually see the terms "system frequency response" and "amplifier frequency response". We must know that the "system frequency response" is always smaller than the range of "amplifier frequency response", so only the label is marked. "Amplifier frequency response" does not make any sense, it is only used to deceive some unsuspecting consumers. Nowadays, the speaker manufacturers generally have a wide range of system frequency response, and there are not many high-frequency parts, but the annotation on the low end is extremely unreal. The foreign famous HiFi (high-fidelity) speakers are also marked with 4, 50Hz or so. And the domestic two or three hundred wooden ordinary speakers actually dare to mark this data, it really makes people laugh big teeth! Therefore, we must tell everyone that the low-frequency sound must be heard, and don't trust the value on the flyer. The music in the multimedia speaker is mainly based on the music, songs, sound effects of the game, background music and the vocal and environmental sound effects in the movie. These sounds are mainly medium and high sounds, so when selecting multimedia speakers It should be more focused on its ability to express sound in the mid-to-high range, rather than the low frequency band. If you really want the cinema effect, then a powerful subwoofer can definitely meet your needs.
4, the strength of sound loudness <br> referred strength, which consists of rapid changes in pressure amplitude (sound pressure) size of the decision. However, the subjective feeling of the human ear is inconsistent with the objective actual intensity. People regard the subjective feeling of strength as the loudness, and the unit of measurement is also decibel (Db), which is based on the sound of 1000Hz sound at different intensities. The ratio of pressure is determined by l/10 of its usual logarithm. The reason for taking the logarithm value is because the increase in intensity and loudness is not proportional to the relationship between the true number and the logarithm! For example, when the sound intensity is as large as 10 times, it sounds like a level (10dB), and when the intensity is as large as 100 times, it sounds two levels (20dB). For a 1000 Hz sound signal, the minimum sound pressure that the human ear can feel is 2×10E-5Pa, and the sound pressure level is set to 0 dB. When the sound pressure exceeds 130 dB, the human ear will be intolerable, so the dynamic range of the human ear hearing is 0 to 130 dB.
People have different sound perceptions with equal intensity and different frequencies; the higher the sound pressure level, the flatter the human auditory frequency characteristics; the lower the sound pressure level, the smaller the human hearing frequency range; the frequency f<16-20Hz and f >18 ~ 20KHz sound, no matter how high the sound level, the human ear can not hear. Therefore, the auditory frequency of the human ear is 20Hz ~ 20KHz, this frequency band is called audio or audio; regardless of the sound pressure level, the human ear is most sensitive to the sound of 3KHz ~ 5KHz frequency.
Most people can't feel the signal sound level abruptly less than 3dB, so the sound system often uses 3dB as the allowable frequency response curve variation range.
5, there is distortion <br> harmonic distortion, intermodulation distortion and transient distortion points. Harmonic distortion refers to the distortion caused by the higher harmonic components that the original signal does not have in the sound playback; the intermodulation distortion mainly affects the tonal aspect of the sound; the transient distortion is due to the existence of a certain inertial mass of the speaker. The vibration of the basin cannot keep up with the difference between the original signal and the playback sound caused by the vibration of the instantaneously changing electrical signal. It is more important in the speaker and speaker system, which directly affects the degree of restoration of the sound quality, so this indicator is closely related to the quality of the speaker. This is often expressed as a percentage, and the smaller the value, the smaller the distortion. The distortion of ordinary multimedia speakers is preferably less than 0.5%, and usually the distortion of the subwoofer is generally large, and less than 5% is acceptable.
6, the sensitivity of the speaker (unit Db)
The sensitivity of the speaker is 3dB, and the sound pressure of the output is doubled. Generally, the sensitivity is 87 Db, the sensitivity is below 84 Db, and the sensitivity is above 90 Db. The increase in sensitivity is at the expense of increased distortion, so as a high-fidelity speaker, it is necessary to reduce the sensitivity requirements for the reproduction and reproduction of the tone. But it can't be said that the sound quality of the speaker with high sensitivity must be bad, and the speaker with low sensitivity must be good. Speakers with low sensitivity are difficult to push (requires a large power reserve for the amplifier). Therefore, although the sensitivity is an indicator of the speaker, it has nothing to do with the sound quality of the speaker. China Home Theater Network
7. Impedance <br> It refers to the ratio of the voltage to current of the speaker input signal. The input impedance of the speaker is generally divided into high impedance and low impedance. High impedance is higher than 16Ω, low impedance is lower than 8Ω, and the standard impedance of the speaker is 8Ω. In the case of the same power amplifier and output power, low-impedance speakers can obtain a large output power, but the impedance is too low, which will cause under-damping and bass degradation. Therefore, although this indicator has nothing to do with the performance of the speaker, it is best not to buy a low-impedance speaker. The recommended value is the standard 8Ω. The impedance of the headphones is generally high impedance - 32 ohms are common. The impedance of the amplifier can generally be labeled as an equivalent impedance, such as an output of 130W at 4Ω, which is roughly equivalent to an equivalent output of 80W. There is a term that is easily confused with the term "damping coefficient", which refers to the speaker impedance divided by the internal resistance of the amplifier source, which ranges from approximately 25 to 1000. The speaker cone is oscillated several times after the electrical signal has disappeared to completely stop the oscillation, and the voltage generated by the coil generates current and magnetic field to prevent this parasitic motion, which is damping. The magnitude of the current, that is, the effect of the damping, depends on the internal resistance of this current flowing through the output stage of the amplifier. This resistance is much lower than the rated impedance of the speaker, typically 0.1Ω, but due to the series resistance and frequency division of the speaker voice coil. The existence of the series resistance of the network, the damping coefficient is difficult to achieve 50.
8, is the ratio of signal to noise ratio <br> normal playback speaker sound signal with the noise signal no signal (power). Also indicated by Db. For example, a tape recorder has a signal-to-noise ratio of 50 dB, which means that the output signal power is 50 dB greater than the noise power. The higher the signal to noise ratio, the lower the noise. The minimum requirements of the International Electrotechnical Commission for signal-to-noise ratio are 63dB for the preamplifier, 86dB for the post amplifier, and 63dB for the combined amplifier. The optimal value of the combined amplifier signal-to-noise ratio should be greater than 90dB; the radio head: 50dB of FM stereo, actually better than 70dB; 56dB (common band) of the tape recording seat, but the signal noise after Dolby noise reduction There is a big improvement. If the noise-to-noise ratio after Dolby B noise reduction can reach 65dB, the signal-to-noise ratio of Dolby C can be up to 72dB after noise reduction (all of them refer to ordinary bands); the signal-to-noise ratio of CD machine can reach more than 90dB, high-grade It can reach more than l10dB. When the signal-to-noise ratio is low, the noise is severe when the small signal is input, and the sound of the entire range is obviously opaque, so speakers with a signal-to-noise ratio lower than 80 dB are not recommended for purchase! The subwoofer 70 Db subwoofer is not recommended for the same reason.
9, speaker material <br> low-end plastic speakers because of its thin body, can not overcome the resonance, no sound quality at all (stupid bear note: not all, the design of plastic speakers is far better than inferior wooden speakers); The speaker reduces the sound of the box resonance, and the sound quality is generally better than the plastic speaker. Usually the multimedia speakers are dual-unit two-way design, one smaller speaker is responsible for the mid-highs output, and the other larger speaker is responsible for the mid-bass output. The selection of speakers should consider the material of these two speakers: the tweeter of the multimedia active speaker is now dominated by the soft dome (in addition to the titanium dome for analog sources), it can reduce the high frequency with the digital source. The hard feeling of the signal gives a gentle, smooth and delicate feeling. Multimedia speakers are now dominated by soft ball tops such as better quality silk films and lower cost PV films. The woofer determines the characteristics of the sound of the speaker. It is relatively important to choose. The most common ones are the paper cones, the plastic paper cones, the paper-based wool basins, the tight-pressing basins, etc. Natural, cheap, good rigidity, lighter material and high sensitivity. The disadvantages are poor moisture resistance and consistency in manufacturing. However, the top-level HiFi system is made up of paper cones because the sound output is very average and the reduction is good. Bulletproof cloth, with wide frequency response and low distortion, is the first choice for those who love strong bass. The disadvantages are high cost, complicated production process, low sensitivity and low light music effect; wool woven pot, soft texture, It is very good for soft music and light music, but the bass effect is not good, lack of strength and shock; PP (polypropylene) basin, it is widely popular in high-end speakers, good consistency, low distortion, all aspects of performance can be circled Can be. In addition, fiber-like diaphragms and composite diaphragms are rarely used in popular speakers because they are expensive. The larger the speaker size, the better. The large-diameter woofer can perform better in the low-frequency part, which can be selected during the purchase. Speakers made with high-performance speakers mean lower transient distortion and better sound quality. Ordinary multimedia speakers woofer speakers are mostly between 3 and 5 inches. Speakers made with high-performance speakers also mean lower transient distortion and better sound quality.
10, the structure and characteristics of the speaker <br> Speakers from the structural form, can be divided into bookshelf and floor-standing, the former is small, clear, accurate positioning, but limited power, low frequency band extension and sense of volume, suitable for Appreciating music lovers who are mainly based on high-fidelity music is also the first choice of our multimedia enthusiasts; the latter is larger in size and more powerful, and the sense of low frequency is more flexible, and it is good at expressing the momentum and powerful shock. However, the level of hierarchy and positioning will be slightly lacking. For lovers of different music, this is also an important part that should be understood before purchasing. Since PC users rarely have the conditions to place large floor-standing boxes, compact desktop bookshelf speakers should be the first choice for multimedia active speakers. In general: as long as the design of the power amplifier module is reasonable, the larger the cabinet, the larger the speaker, the more the sound is heard.
11. Scalability <br> This refers to whether the speaker supports multi-channel simultaneous input, whether there is an output interface connected to the passive surround speaker, and whether there is a USB input function. The number of subwoofers that can be connected to the surround speakers is also one of the criteria for measuring the performance of the expansion. The interfaces of ordinary multimedia speakers mainly include analog interfaces and USB interfaces. Others such as optical interfaces and innovative digital interfaces are not very common, so they are not introduced.
12, sound technology <br> hardware 3D sound technology is now more common SRS, APX, Spatializer 3D, Q-SOUND, Virtaul Dolby and Ymersion, etc., although they each implement different methods, but can make people feel Obvious three-dimensional sound field effects, of which the previous three are more common. They all use the extended stereo (Extended Stereo) theory, which is to add additional processing to the sound signal through the circuit, so that the listener feels that the sound image orientation is extended to the outside of the two speakers, thereby expanding the sound image and giving people space. Sense and three-dimensionality, resulting in a wider stereo effect. There are also two sound enhancement technologies: active electromechanical servo technology (essentially using the Helmholtz resonance principle), BBE high-definition plateau sound reproduction system technology and "phase fax" technology, which also has a certain effect on improving sound quality. For multimedia speakers, the SRS and BBE technologies are relatively easy to achieve and can effectively improve the performance of the speakers.
13, <br> tone refers to a specific and generally stable pitch signal, the popular talk is to listen to the tone of voice high and low degree. It depends mainly on the frequency and also on the sound intensity. The high-frequency sound of the human ear is a high-pitched, low-frequency sound. The human ear responds with a low pitch. The pitch is substantially logarithmic with frequency (Hz). Different instruments play notes of the same frequency. Although the sounds are different, their pitches are the same, that is, the fundamental frequency of the playing sound is the same. China Home Theater Network
14, <br> sound sense of sound quality, but also a sound different from another characteristic quality sound. When different instruments are emitting the same tone, their colors can be different. This is because their fundamental frequencies are the same, but the harmonic components are quite different. Therefore, the tone depends not only on the fundamental frequency, but also on the harmonics that are integral multiples of the fundamental frequency, which makes each instrument and each person have a different tone.
15, the dynamic range of the strongest and weakest <br> sound ratio, expressed as Db. For example, a band has a dynamic range of 90 dB, which means that the power of the weakest part is 90 dB lower than the loudest part. The dynamic range is the ratio of power, independent of the absolute level of sound. As mentioned earlier, the human ear has a dynamic range from 0 to 130 dB. The dynamic range of various sounds in nature is also very variable. The general language signal is only about 20 to 45 dB, and some symphonies have a dynamic range of 30 to 130 dB or higher. However, due to some factors, the dynamic range of the sound system rarely reaches the dynamic range of the band. The inherent noise of the recording device determines the weakest sound that can be recorded, and the maximum signal capacity (distortion level) of the system limits the strongest sound. Generally, the dynamic range of the sound signal is set to 100 dB, so the dynamic range of the audio device can be 100 dB, which is very good.
16, total harmonic distortion (THD)
Refers to the extra harmonic component of the output signal caused by the nonlinear component compared to the input signal when the audio signal source passes through the power amplifier. Harmonic distortion is caused by the fact that the system is not completely linear. We use the new root mean square of the total harmonic component and the percentage of the original signal rms. For example, an amplifier that adds 1000 Hz of Lv at 1000 Hz output 10 V, then has 10% second harmonic distortion. The sum of all additional harmonic levels is called total harmonic distortion. In general, the total harmonic distortion at 1000 Hz is the smallest, so many products use the distortion of this frequency as its index. However, total harmonic distortion is frequency dependent, so the US Federal Trade Commission stipulated in 1974 that total harmonic distortion must be measured in the full audio range of 20 to 20,000 Hz, and the maximum power of the amplifier must be at a load of 8 ohms, total The harmonic distortion is measured under less than 1%. The minimum requirements for total harmonic distortion specified by the International Electrotechnical Commission are: 0.5% for the preamplifier and 0.7% for the combined amplifier, but in fact can be less than 0.1%: the FM stereo tuner is less than or equal to 1.5%, in fact Can be done below 0.5%; laser phonograph can achieve less than 0.01%.
Since the current method of measuring distortion is a single sine wave, it does not reflect the full picture of the amplifier. The actual music signal is a composite wave of different speeds, including dynamic indexes such as rate conversion and transient response. Therefore, high-quality amplifiers sometimes also indicate parameters such as intermodulation distortion, transient distortion, and transient intermodulation distortion. (l) Intermodulation distortion (IMD): Synthesize a harmonic signal of 125 Hz and 1 kHz output from the intermodulation distortion meter, input it into the amplifier to be measured according to the amplitude of 4:1, and measure the intermodulation from the rated load. Distortion coefficient.
(2) Transient Distortion (TIM): The square wave signal is input to the amplifier and its output waveform envelope is retained. If the conversion rate of the amplifier is not enough, the square wave signal will be deformed and transient distortion will be generated. Mainly reflected in the fast music mutation signal, such as percussion instruments, piano, xylophone, etc., if the transient distortion is large, the crisp music will become ambiguous.
(3) Transient intermodulation distortion: Mixing a 3.15 kHz square wave signal with a 15 kHz sine wave signal at a peak-to-amplitude ratio of 4:1, and after adding an amplifier, newly add the product RMS of all intermodulation distortions to the original sinusoidal amplitude. percentage. If the amplifier adopts deep loopback negative feedback, the transient intermodulation distortion is generally large, which reflects the sound sluggish, stiff, and non-presence; on the contrary, the sound is smooth, delicate and natural.
17. Stereo Separation <br> Refers to the ability and degree of interference between two channels without interference, that is, the degree of isolation, usually the difference between the signal level in one channel and the level leaked into another channel. Said. If the stereo separation is poor, the stereoscopic effect will be weakened. The minimum index of stereo separation specified by the International Electrotechnical Commission is 40dB greater than or equal to 40dB at lKHz, and it is better to achieve 60dB of dryness. The stereo separation of FM stereo broadcasts specified by the European Broadcasting Union is >25dB, which can actually achieve 40dB or more. . Stereo channel balance refers to the difference between the left and right channel gains, which is generally expressed as the maximum difference between the left and right channel output levels. If the imbalance is too large, the stereo pan position will deviate and the indicator should be less than 1 dB. China Home Theater Network
18. Damping coefficient <br> is the ratio of the rated load (speaker) impedance of the amplifier to the actual impedance of the power amplifier. A large damping coefficient means that the output resistance of the power amplifier is small, and the damping coefficient is the ability of the amplifier to control the movement of the speaker cone after the signal disappears. An amplifier with a high damping coefficient is more like a short circuit to the speaker and reduces its vibration when the signal is terminated. The output impedance of the power amplifier directly affects the low-frequency Q of the speaker system, which affects the low-frequency characteristics of the system. The Q value of the speaker system should not be too high, generally in the range of 0.5 to 1. The output impedance of the power amplifier is a factor that causes the low frequency Q to rise. Therefore, it is generally desirable that the output impedance of the power amplifier is small and the damping coefficient is large. . The damping coefficient is generally between tens and hundreds, and the damping coefficient of high-quality professional power amplifier can be as high as 200 or more.
l9, loudness control which action is to enhance <br> high and low frequency acoustic low volume. Since the human ear has poor hearing sensitivity to high frequency sound, especially low frequency sound, it is required to perform auditory compensation for high frequency and low frequency at low volume, that is, it requires a large increase in low frequency and a certain increase in high frequency. In other words, when the volume is reduced, the decrease in the low frequency portion of the signal is less in the higher frequency portion. Equal loudness control satisfies this requirement, and equal loudness control is generally 8dB or 10dB.
20, 3D sound field processing and surround sound <br> Why do ordinary two speakers make us hear what does not exist is like the sound behind the back? As we all know, stereoscopic film is the illusion of the eyes and the generation of three-dimensional sound field Can not do without the illusion of the ear. Various hardware 3D sound technologies such as SRS, virtual Dolby and software 3D technologies such as EAX, A3D, etc. are fully researched new technologies introduced by the human ear to reduce the cost after receiving the principle of sound. In essence, the effect of completing a three-dimensional sound field through multiple speakers is much better than the sound field of two speakers. Therefore, surround sound should be based on multi-speaker configuration. Their sense of positioning and space is strong. Let's take a look at what kind of real surround sound:
A Dolby Pro-Logic surround sound system
The 4-2-4 encoding technology encodes the audio information of the left, middle, right and rear sides into two channels on the left and the right; when the sound is played, it is decomposed from the left and right channels by the decoder to restore the original 4 Channels, these four channels are commonly referred to as: front left channel, front center channel, front right channel, and rear surround channel. Scientific experiments have shown that in order to obtain the immersive real sound effect, a sound field environment surrounded by the listener must be generated around the listener. The more channels used by the whole sound system, the stronger the sound field positioning of the listener. The more realistic the feeling of being on the ground. According to the current audio-visual environment of the general family, the sound system uses five channels to meet the sound field positioning needs. Therefore, the Dolby Pro Logic surround sound system mostly uses 5 channels. On the surface, the 5-channel Dolby Pro Logic Surround Power Amplifier does have five power outputs: front left channel, center channel, front right channel, surround left channel (also known as rear) Left channel) and surround right channel (also known as rear right channel), but the surround signal output from the decoder in the Dolby Pro Logic Surround system is mono, and the left and right of the 5-channel power amplifier The two surround channels are connected in series inside the amplifier. Therefore, strictly speaking, it is more suitable to refer to them as 4-channel power amplifiers.
B, THX home theater system
THX is not a stand-alone sound system. It only performs proper post-processing on the stereo signals processed by Dolby Pro Logic to obtain real sound effects with accurate sound positioning and large dynamic range. Therefore, we say that THX is a standard built on Dolby Pro Logic to measure home theater sound systems. China Home Theater Network
The THX system, which has a THX controller more than the decoder in the Dolby Pro Logic Surround System, is the post-processing circuit for the Dolby Pro Logic decoder, which is subwoofer EleGtric Crossover ), Re-Equalizer, De-Correlation, and Timbre Matching. The role of the ultra-low frequency electronic crossover is to separate the ultra-low frequency channels from the three front, left, and right front channels, increasing the dynamics of the three channels. The space of the cinema is large. In order to adapt to the playing environment of the cinema, the film specially enhances the high-frequency components of the sound during the production process, so that the sound can be vivid. However, the environment of the home theater is very small. When the same movie is played at home, it will appear too high and the treble is too bright. The function of the equalization circuit in the controller is to rebalance the sound so that the sound is not too bright. The function of the de-correlation circuit is to convert the mono signal transmitted to the surround channel into two channels on the left and right by an analog method, so that the sound effect is more realistic. The sound quality matching circuit is used to modify the difference between the sounds of the front channel and the surround channel. When the sound moves from both sides and the rear side of the front direction, the listener does not feel the change of the tone.
C, AC-3 Dolby Digital surround sound system developed by Dolby Laboratories <br> in 1991, a kind of Dolby Digital surround sound system (Dolby Surround DigitaI), ie AC-3 system. The AC-3 Dolby Digital Surround System consists of five fully independent full-range channels and one ultra-low frequency channel, sometimes referred to as 5.1 channels. The five independent channels are: front left channel, front right channel, center channel, surround left channel and surround right channel; there is also a special low frequency for playing back below 120Hz. The channel is 0.1 channel. The Dolby Digital Surround System has the following features compared to the Dolby Pro Logic Surround System and the THX system:
First, the AC-3 system uses 5.1 completely independent channels during recording, decoding, and playback, improving the signal-to-noise ratio of the signal and the separation between channels.
Second, the surround channel is digital stereo, the two channels are completely independent, and the high-frequency playback upper limit is extended from the original 7 kHz to 20 kHz, which is the full-range surround sound, making the surround sound more expressive.
Third, the subwoofer in the AC-3 system uses a separate recording track during recording, and the signal is emphasized. Although the decoder in the THX system also has ultra-low frequency signal output, its subwoofer is from the original. Separated from the four-channel signal, the acoustic effects of the two are quite different.
Fourth, the AC-3 system increases the output power of the surround channels, so that 5.1 channels have sufficient output power. Simply put: the audio of the current DVD movie is recorded using the AC-3 specification. With the corresponding decoding system and speaker system, you can appreciate the home theater style.
D, DTS (DigZtal Theater Systems) digital cinema system <br> Digital cinema system is a new technology in the home theater surround sound technology. It is also a 5.1 audio system, namely left channel, right channel, center channel, left surround channel, right surround sound and subwoofer channel. The DTS system is also an all-digital multi-channel surround sound technology. DTS differs from the digital AC-3 in that the Dolby Digital has a high compression ratio, and the encoding uses a large deletion of a weak detail signal that is theoretically considered redundant. Reduce the amount of data for the purpose. Therefore, the compression ratio of Dolby Digital encoding is very high (up to 12:1), which also causes some loss of fine signals. DTS starts with improving the utilization of digital space, so that the information data can be fully utilized. Therefore, its compression ratio is only 3:1, and its sound reproduction is obviously higher than that of Dolby Digital. Because the DTS system loses few signals during encoding and retains the rich subtle signals in the original sound field, its sound field is superior to Dolby Digital in terms of continuity, exquisiteness, breadth and level. The DTS system is now the best 5.1 channel surround sound technology on the market.
TECHNOLOGY
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