Weak current College】 【broadcast a detailed description of the system design.

<br> <br> A), the public broadcasting system overview <br> <br> Public broadcasting system is a sound sound system in a branch, but sound amplifying sound system also known as professional audio systems involve acoustical sound, and music of .three interdisciplinary science disciplines. So the public broadcasting system ultimately involved is reasonable, proper audio system design and debug, good sound propagation environment (acoustical conditions) and the precise spot tuned combination of the three best, are complementary to each other. <br> .<br> Public broadcasting as a system problem, system design must consider these issues. In the select performance of electro-acoustic devices, adopted on the basis of careful design of the system, careful system debugging and good acoustical conditions, achieved electro-acoustic .musical, natural sound effects. <br> <br> Broadcasting system category: <br> <br> The broad sense of the broadcasting system includes sound reinforcement system and reproducing system for two broad categories: <br> <br> 1, sound .reinforcement system: speaker and microphone at the same sound, there are sound feedback and room resonance of Whistler, distortion and oscillation phenomena. To ensure system stability and uptime, the highest available system gain than acoustic feedback self-excited 6dB gain low criticality. < .br> <br> 2, reproducing system: the system only tape drives, CD player, sound source, microphone, sound feedback may not exist, acoustic feedback coefficient is 0, which is a special case the broadcasting system. <br> <br .> Public broadcasting system by purpose can be divided into the following categories: <br> <br> 1) outdoor broadcast system. <br> <br> Outdoor broadcast system is mainly used in the stadium, stations, parks, art Plaza, music .fountain, etc. It is characterized by service area, the space is wide. Background noise; sound travels to direct sound; required sound pressure level is high, if such reflection around the high-rise buildings, speaker layout objects without reasonable, Sonic, .formed by multiple reflection exceeds 50ms latency above, double or multiple sound, serious problems such as echo occurs, impact sound clarity and sound like positioning. Outdoor system sound effect is also affected by weather conditions, wind direction and impact of environmental noise, etc. .<br> <br> 2) indoor radio system <br> <br> Indoor radio system is the most widely used system, including all kinds of theatre, sports, dance halls, etc. It professional is very strong, both non-language .sound reinforcement, and for various theatrical performances, at the request of the sound quality is very high, and system design should not only consider technical issues, but also audio related architectural acoustics. Room shape on the sound quality has a greater impact. <br .> <br> 3) public broadcasting system: <br> <br> Public broadcasting system for hotels, commercial buildings, ports, airports, subway, schools provide background music and radio programs. In recent years, the public broadcasting system and make an .emergency broadcast, and interactive fire alarm system. Public broadcasting system of control functions. If all call selection broadcast and radio features, mandatory work for features and functions of the priority right to broadcast, etc. Speaker load and dispersion, transmission lines long. To .reduce the transmission line losses are generally set using 70V or 100V voltage high impedance transmission. Request not high sound pressure, the sound quality to baritone and treble-dominated. <br> <br> 4) Conference system <br> <br> With .the domestic and international exchanges have increased in recent years, teleconferencing, video conferencing and digital conference system (DCN) developed very rapidly. Conference system widely used in the Conference Center, hotels, and Government agencies. Conference system including the Conference discuss the system, .voting systems, simultaneous translation system and videoconferencing system. Requirements for audio, video (image) system synchronization, all used computer control and storing session data. <br> <br> <br> (2), radio system characteristics <br> < .br> Short background music is Backgroundmusic's BGM, its main role is to mask the noise and to create a relaxed atmosphere, to hear if anyone does not listen, you will not be able to identify its source location, the volume is small, is a .way to create an atmosphere of relaxed environment. Therefore, the background music of effect has two, one is psychologically cover environmental noise, the second is to create and adapt the indoor environment, an atmosphere of its hotels, hotels, restaurants, shopping malls, .hospitals, office buildings etc. <br> <br> (3), the composition of broadcasting sound system <br> <br> No matter what kind of broadcasting sound system, the base can be divided into four sections: shows devices, signal .amplification equipment, transmission lines and speaker system. <br> <br> Program source: program source is typically a radio, CD player and recorder deck and other equipment to provide, in addition to the microphone, electronic musical instruments, etc. <br .> <br> Signal amplifiers and handling equipment: including equalizer, preamplifier, power amplifier and a variety of controller and audio processing devices. This part of the device's first task is to signal amplification, the second is the signal selection. Mixer and preamplifier role .and status of similar (and of course a mixer functionality and performance indicators higher), their basic function is to complete the signal pre-amplification of choice and, in addition to taking on the volume and sound effects for various adjustment and control. Sometimes in .order to better frequency balance and tone beautification, also separately into the graphic equalizer. This part is the entire broadcast sound system of the "control center". Power amplifier the preamplifier or mixer sent signals power zoom, and then through the transmission lines to promote .speakers reproducing. <br> <br> Transmission line: transmission line is simple, but as the system and transmission method has different requirements. The Hall, theatre, etc., due to the power amplifier and speaker distance, generally use low resistance and .high current direct feed, transmission line requires a dedicated speaker cables, and the public broadcasting system, as the service area, long distance, in order to reduce the losses caused by the transmission lines, often using high pressure transmission, transmission current small, less .demanding on the transmission line. <br> <br> Loudspeaker: the loudspeaker system requires that the entire system of matches, while the choice of its location but also realistic. Hall, theatre, singing tone, while the speaker generallyHigh power speaker; the .public broadcasting system, because it is not high on the tone to be used is in the ceiling loudspeaker 3W-6W. <br> <br> (Iv), public broadcasting engineering system design <br> <br> Public broadcasting system design usually .start from sound field (that is, the placement of the speakers), and then back to a power amplifier, sound processing systems, sound mixer, until the receiver and other audio sources. This step by step backward propulsion design steps are taken for granted .. Because sound field design is to meet the system function and sound basis, it involves the selection of the speakers system for sound schemes and signal paths, etc. Only determine speaker system to power amplifier driving power of calculation and determination of driving signal path, .and then under the driving power distribution scheme in .. <br> <br> (5), system design must consider several technical parameters <br> <br> Includes: audio gain, language definition, the biggest boost level. <br> .<br> 1) acoustic gain <br> <br> Project owners may first be asked sound reinforcement system can open multiple ringing? what technical parameters used to measure? this issue in Europe and the United States expressed with voice gain (EASE or other .acoustic design software using this parameter). In China and the former Soviet Union using acoustic gain. <br> <br> Sound reinforcement system for acoustic gain (or voice gain) acoustic feedback factors limit, you cannot open the speakers to be able to .achieve the maximum sound pressure level. <br> <br> Sound reinforcement system is switched on, increasing system amplifier gain, gain increased to a certain location, speakers of some sound propagation through space to the microphone input collected, at which point the microphone .output produces a signal that the amplitude of size equal to or greater than the original input signal for a cycle or its integer x, this process can continue, that is not needed outside of the input signal will produce output, the system enters feedback (whistling .generating system). Whistling sound reinforcement system enters a critical state, although also shown below to hear the shrill whistling cry, but the system's frequency response appears extremely irregular changes sound great distortion occurs. You want the system to function properly, the system of 6dB .gain should be left to the remainder, whistling away from the system (System of self-excited) in a critical state. So we can get audio gain is defined as: <br> <br> Acoustic gain: sound reinforcement system meet the highest .available gain (6dB gain critical gain less NPSH.of), specify the location of the audience on measured the average sound pressure level and microphone at the sound pressure level difference between the number of dB. <br> <br> Voice gain: System .open and increases to the maximum available gain, in the specify the location of the audience on measured the average sound pressure level (dB) minus the system shuts down at the same audience position measured the average sound pressure level in dB., <br> .<br> The above two definitions expressed the same acoustic feedback physical phenomena, they differ only in that the different measurement methods and the methods of expression. Gain a clear idea of the sound, the capacity to understand, explain the audience area using sound reinforcement .system and do not use sound reinforcement system for numerical increase of sound pressure level. But in the actual measurement, if measurement points of the original sound source, environmental noise is larger, it is difficult to correctly detect the system shuts down sound source arrives at .the measuring point of sound pressure level. Acoustic gain represents the average audience area average sound pressure level with the sound pressure level at the microphone of the margin (dB), if we know the microphone's sound pressure, so you can immediately calculate the audience area .average sound pressure level, for example; usually the speaker's mouth when away from the microphone, microphone 0.5m branch of the sound pressure level is approximately 70dB, if the system's audio gain to-6dB, so you can find the audience area average sound pressure .level for 70dB-6dB = 64dB, if you also want to increase the audience area of the sound pressure level, you can put the microphone close to the speaker's mouth, such as the distance from 0.5m to 0.125m (125mm) then the microphone ., the sound pressure level can be increased to 82dB (distance reduced 4 x sound pressure level can improve 12dB) at this point the audience area average sound pressure level can also be increased to 76dB, note: sound gain is + dB value; acoustic gain .is-dB value, actual can do the highest audio gain-6Db. <br> <br> System maximum usable voice gain Gmax-formula available under <br> <br> Gmax = 20lgD0-20lgDS +20 lgD2-b (dB) < .br> <br> Type 0 to speak to the audience and the distance between units of m; <br> <br> Ds speaker distance between the microphone, the unit is m; <br> <br> D1-speakers to microphone distance ., m; <br> <br> D2 for the speakers to the distance between the audience, the unit is m; <br> <br> Acoustic feedback (single pulse signals to produce a series of pulses) <br> <br> .Top-can reach the following conclusions: <br> <br> 1. voice gain or audio gain does not depend on the speaker's sound pressure level; <br> <br> 2. shorten the speaker and microphone distance between DS, which can .effectively improve sound gain; <br> <br> 3. increase the microphone and speaker distance D1, can increase the voice gain; <br> <br> 4, with strong links to nature and the nature of the excellent speaker system can improve .the audio gain. <br> <br> Heart-shaped microphone not can improve more voice gain? in practical work too much reliance on directivity microphone and directivity speaker to improve the system gain is unwise, because the microphone and speakers to characteristic is the .frequency of changes, when the low-frequency close to the non-directivity characteristics. Most designers use their points to the characteristics of the sound is not greater than 6dB gain boost. <br> <br> Indoor sound reinforcement system voice gain subject- .<br> <br> (4) restrictions and microphone, speakers, pointing to the physical effects, also subject to room acoustical conditions. In addition to electro-acoustic system can take feedback automatically suppressor to reflex the strongest frequency and amplitude maximum room resonance .frequency absorption off, but uptake of frequency points not exceeding 5 ~ 6 point frequency. <br> <b> </ b> R> 2) articulation <br> <br> Articulation is sound reinforcement system of important technical indicators. Language definition .is an evaluation system for intelligibility. Language definition of the main factors are: <br> <br> 1. sound pressure level and background noise pressure level ratio 2 <br> <br> Good articulation calls language sound pressure is greater than the background .noise pressure level 25dB. If this ratio at 10 ~ 15dB, clarity will be lower, but still within the allowable range. Background noise from indoor and outdoor environment noise, air conditioning, ventilation and noise and crowd noise, etc. <br> < .br> 2, the reverberation time <br> <br> Speech speed medium, every seconds can out 3 to 4 syllables, so 1.5 seconds shorter reverberation time, clarity of the language. <br> <br> 3, direct-to- .noise and reverberation time of sound energy ratio <br> <br> Reverberation time exceeds 1.5 seconds, the language definition is reverberation time and direct-to-noise and reverberation sound better than as a function of time. <br> <br> Maximum .sound pressure level 3) <br> <br> Sound reinforcement systems in the highest available gain State-infeed speaker system voltage corresponds to the design of power (or the sound is rated power) voltage value in system requirements for the frequency range, the .measurement point measured every 1 / 3 octave band sound pressure level averaged. and then add 6dB signal peak factor to get the maximum sound pressure level. Test signal source for pink noise + 1 / 3 octave band-pass filter. <br> <br .> D define: Auditorium sound field of the steady state is maximum sound pressure level: <br> <br> To technology parameters description system maximum sound pressure level of potential. To prevent damage to the test of time is too long, speaker speaker system .system-infeed power can take 1 / n (n = 2-10), each measuring point of maximum sound pressure level calculated under type available: <br> <br> Type: Li-the first 1 / 3 octaves frequency bands of sound .pressure level <br> <br> N is the transmission frequency range 1 / 3 octaves frequency bands. <br> <br> (Vi), radio speaker selection and configuration <br> <br> 1. selection of the radio speakers < .br> <br> In principle, should be considered as environmental specifications for the selection of different varieties of broadcast speaker for example, in a ceiling, ceiling-mounted indoor, use embedded, not the back cover of the ceiling speakers. The speakers structure .simple, the price is relatively cheap and easy construction. The main disadvantage is that there is no back cover, susceptible to insects and rodents bite. <br> <br> The only frame ceiling surface no ceiling Interior (such as the us shopping centre .)-spherical speaker used for hoisting or back cover of the ceiling speakers. <br> <br> Since the ceiling is equivalent to an infinity of baffle, so there is a ceiling conditions the use of the back cover of the speakers also does not .cause a short circuit. And when the situation without ceiling, if you still use no speakers back cover of smallpox, the effect is very poor. This principle should use hoisting speakers. However, if such investment, you can also use the back cover of .the ceiling speakers. Have the back cover of the back cover of ceiling speakers not only general mechanical protection and, to a certain extent, the effect of preventing from short circuit. <br> <br> In ceiling-mounted indoor (such as the .underground car park) is to choose wall-mounted speakers or indoor sound columns. <br> <br> Outdoors, use outdoor sound columns or horn. This type of code string and Horn is not only waterproof function, but the volume is large. .Due to the spacious outdoor environment, no reverberation effect select volume larger variety is necessary. In the garden grass grassland, to choose speakers. This type of speaker waterproof, beautiful, and the volume and audio quality are very high. <br> <br .> The decoration is fastidious, ceiling high wide Hall Grand, to choose elegant tone harmony of hoisting-and-speakers. As for brands and grade selection, natural and investment. <br> <br> (VII), the choice of radio power .amplifier <br> <br> Radio power amplifier is different from the HI-FI amplifier. Its main feature is a 70V and 100V voltage output terminals. This is because the broadcasting channels are usually very long, you can reduce the required high voltage transmission .line loss. <br> <br> Radio power amplifier of the most important parameter is the rated output power. Should use the rated output power, subject to the total power of the radio speakers. The broadcasting system, as long as broadcast speaker power .less than or equal to the amplifier's rated power and voltage parameters are the same, you can feel free to adapt, but considering the line loss, aging and other factors, should be appropriate to leave power. According to the "standard" requirements, PA .equipment capacity (corresponding to the rated output power) should generally be anxiashijisuan:: <br> <br> P = K1 × K2 × ΣP0 <br> <br> P-power into a device output total power <br> <br .> P0-each tap (equivalent to partition) at maximum power when broadcasting) <br> <br> Pi-the I partition speakers rated capacity <br> <br> TKi-the I partition at the same time need to factor: < .br> <br> Service broadcasting room programs, take 0.2 ~ 0.4 <br> <br> Background music, take 0.5 ~ 0.61 <br> <br> The business of broadcasting, 0.7 ~ 0.8 <br> <br> As fire radio ., take 1.0 <br> <br> K1-line attenuation compensation coefficient: 1.26 ~ 1.58 <br> <br> K2-aging coefficient: 1.2 ~ 1.4 <br> <br> Made sure of this, if this is the background music .system, broadcasting amplifier's rated output power shall be broadcast speaker total power of 1.3 times. However, all of the public broadcasting system in principle should be can't casualty emergency broadcast. Therefore, the system shall be provided with emergency radio power amplifier. According .to the "standard" requirements, emergency broadcasting amplifier's rated output power is the largest radio speakers and three in the speaker volume totals 1.5 times. As regards broadcasting amplifier of other specifications that depend on the specific structure of the broadcasting system and investment. <br .> <br> (VIII), broadcasting Division <br> <br> APublic broadcasting system is often divided into several zones, from the management (or pre-programming) decide which area shall be the regional broadcasting distribution shall be suspended, the broadcast ., the region shall insert the emergency broadcast ... And so on. <br> <br> In principle, the partition scheme depends on the customer's need is often refer to the following rules: <br> <br> 1. building usually .floor partition; shopping malls, playground, usually to sector partition; sports often stand partition; residential resort, usually by property management Division, and so on. <br> <br> 2. the Department of management, and public places should be located .. <br> <br> 3. important departments or broadcast speaker volume need to be adjusted in the field should be set up individually. <br> <br> In General, the partitioning is designed for easy management. Anyone who needs to be .treated separately in part, should be split in different areas. However, each region, the total power of the radio speakers should not be too large, partition, and the capacity of the power amplifier. <br> <br>.