【 Weak current College 】 public broadcasting system (1)

First, the public broadcasting system overview
Due to natural sound sources (such as speech, singing, musical, sound playback, and so on) of the sound energy is very limited, their sound pressure level with increased communication distance attenuation, coupled with the effects of environmental noise, so that the sound source of transmission distance is limited, so in a public place must use electronic technology — make amplification of sound reinforcement, audio system will sound source signal amplification, increase audiences the sound pressure level area, ensure that every Member of the audience receive appropriate sound pressure level.
Public broadcasting system (PublicAddressSystem abbreviation PA) belong to the sound reinforcement audio system, a branch from factories, schools, hotels, stations, terminals, the square to the venue, theater, Stadium, residential district, are closely associated with it.
Public broadcasting system is a system that requires electronics, electro-acoustic techniques, Architectural Acoustics technology and Sonic arts and other disciplines, in close collaboration with the public broadcasting system of sound effects not only on the overall performance of electro-acoustic systems, also with sound environmental architectural acoustics and field tuning use are closely related, so the public broadcasting system ultimately require proper and reasonable electro-acoustic system design and debug, good sound propagation conditions and the correct field tuning techniques are the best fit, three are mutually reinforcing. In system design must consider these issues, the choice of good performance on the basis of electro-acoustic equipment, through careful design of the system, careful system debugging and good acoustical conditions, electro-acoustic musical, natural sound effects.
(A), the characteristics of the public broadcasting system
Background music (BGM Backgroundmusic "), 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.
Public broadcasting system includes background music and emergency broadcasting features, usually, it is a public place, in the corridors, Elevator entrance, elevator car, halls, shopping malls, restaurants, bars, ballrooms, community garden, and other points of the combined sound columns or distributed speaker boxes, usually play background music, when emergency, strong cut for the emergency broadcast, it is used to command the evacuation.
Public broadcasting system of control functions, such as broadcasting and all call selection broadcast function, mandatory switching and priority radio functions. Public broadcasting system 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. This system of broadcasting with microphone and speakers to public broadcasting are generally not at the same room, so silent feedback.
(2), the CENTRE public broadcasting system of classification
1. the public broadcasting system in accordance with the transmission, signal processing methods can be divided into the following categories:
1.1 traditional public broadcasting system: traditional public broadcasting system through audio line analog power signal transmission to the Terminal on the speakers to the engine room of power amplifiers to speakers is the use of high-voltage transmission, usually 100V or 70V, their advantage is line loss-less, easy load-join, just put the speaker with step-down transformer and received online.
1.2 digital addressable public broadcasting system: the real significance of the digital addressable public broadcasting system its audio signal, control, signal and communication in the digital domain, has a long transmission distance and better transport, especially the audio signal and control signals in a two-core of twisted pair transmission, not only greatly saves installation and wiring costs, but also for the future of system maintenance and system's high reliability provides prerequisite.
1.3 streaming media (IP) intelligent digital broadcasting: streaming media (IP) intelligent digital broadcasting is based on the Internet and LAN network of pure digital audio broadcast system, different from the traditional analog audio, FM, addressing and NC broadcast broadcasting systems, streaming media (IP) intelligent digital broadcasting system is fully compatible with existing Internet and LAN, TCP/IP Protocol, the application without wiring, you can leverage your existing network or the internal LAN; embedded hardware terminal, the ability to set separate IP address available through multilayer switches, host can control the settings of each terminal and play, the more you can select the options you want on the Terminal in the programme; the use of computer technology, the system is almost compatible with all audio formats, using the IP technology, content can be played without any restrictions, each terminal can play needs of program content. To be able to completely replace based on analog or digital broadcast system of traditional intelligence, truly on the Internet or LAN IP audio broadcasting features, support for broadcast, live, on-demand, and supports a wide range of popular applications.
2. the public broadcasting system in accordance with the use of functions and properties can be divided into the following categories:
2.1 business of broadcasting system: this is a business and executive management as the main language of broadcast, for Office, commercial, offices, schools, railway stations, ports, airports and other places, the business of broadcasting usually consists of departments of management;
2.2 service broadcasting system: this is to enjoy the background music as a service in the nature of broadcasting system, often used in hotels, restaurants, banks, securities, parks, squares and large-scale public events etc.
2.3 emergency broadcasting system: this is used to meet in fire and other emergency evacuation guide requirements, and other objective broadcast system designed, usually broadcast systems and on the two systems combined use, combined with design-time, first press the emergency broadcast system requirements to determine the system;
2.4 conference system: 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, audio, video (image) system synchronization, all used computer control and storing session data.
3. the public broadcasting system in accordance with the use of space can be divided into the following categories:
3.1 outdoor broadcast systems: 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.
3.2 indoor radio system: 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.
(3), the composition of the public broadcasting system
No matter what kind of broadcasting sound system, the base can be as shown in Figure 1 is divided into four sections: program source device, signal amplification equipment, transmission lines and speaker system.
1. program source: program source is typically a traditional such as: DTU-6300 digital tuner, MPT-6000/6000A multimedia player and so on; intelligence such as: DPC-9800 digital program control centre, DPP-9300 campus radio player, DPP-9310A digital audio source Studio machine, DPP-9330 NC MP3 player and so on, they are all built-in digital audio sources, and related systems for control of the device. There are also some such as radio, CD player and recorder deck equipment, in addition to the microphone, electronic musical instruments, etc.;
2, signal amplifiers and handling equipment: including equalizer, preamplifier, power amplifier and a variety of control equipment 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 functions are complete signal pre-amplification of choice and, in addition to 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 theentire broadcast sound system of the "control center". Power amplifier the preamplifier or mixer sent signals power zoom, and then go through the transmission lines; promoting speakers reproducing
3, transmission lines: transmission line is simple, but as the system and transmission method has different requirements, is generally divided into four types, such as analog audio circuits, digital twisted pair line, streaming media (IP) data networks lines, CNC fiber-optic lines.
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, so do not ask for much of the transmission lines, generally use ordinary audio line, belongs to the analog audio line;
Digital addressable public broadcasting systems generally use digital transmission twisted-pair to, it is to connect the audio signal and control signals in a two-core of twisted pair transmission, not only greatly saves installation and wiring costs, but also for the future of system maintenance and system's high reliability provides preliminary favorable conditions, have further transmission distance and better transmission of results;
At present most of the schools, corporations and other public places are already have a streaming media (IP) data networks line (LAN line), for streaming media (IP) of the public broadcasting system is on this basis simply streaming media (IP) of the public broadcasting system devices added, directly with the original streaming media (IP) data networks lines for transmission, do not need separate wiring;
Because in many places such as parks, community, public broadcasting area larger, transmission lines, transmission mode you can use CNC optic line to wear lose, transmission distance up to 20-200KM, thus solving the past public broadcasting system cannot make long-distance transmission of disadvantages.
4. loudspeaker: the loudspeaker system requires that the entire system of matches, while the choice of its location but also realistic, indoor general ceiling loudspeaker, indoor sound columns, Wall Mount speaker or hanging speakers, outdoor use outdoor sound columns, lawn dedicated speaker, Horn, and so on.
Appendix: national standards
Cablecasting and fire radio design installation specification (excerpt)
1993 People's Republic of China Ministry of the civil construction electrical design code (JGJ/T16-92) to cablecasting and accident broadcast design, installation, and so there are a number of specific provisions, the extract below for the day-to-day management of the design and as a reference:
21. a cablecasting
21.1.1 public building cable system should be established. System of categories should be based on the nature of building size, use, and functional requirements. Cablecasting generally can be divided into:
(1) the business of broadcasting system.
(2) service broadcasting system.
(3) fire broadcasting system.
21.1.2 office buildings, buildings, schools, railway stations, ferry terminals and airports, and other buildings, there should be a business of broadcast, meet the business and administrative managementLogic-based language broadcast requirements. The business of broadcasting should be determined by the competent departments management.
21.1.3 one to three levels of the hotel, the large public places should be set in the service broadcast, meet to enjoy sex music broadcast-based requirements. The hotel service broadcast not more than five sets.
21.2.4 from amplifier device output to the line up of user speaker box between line attenuation should meet the following requirements:
(1) the business of broadcasting should not be greater than 2dB (1000Hz).
(2) service of broadcasting should not be greater than 1dB (1000Hz).
21.2.6 using fixed output voltage, output voltage feeder lines use 70V or 100V.
21.2.8 program and telephone line combined with a cable TV signal transmission level should not be greater than 7.8dB. When the signal line numbers more, use a dedicated cable.
21.3.2 cable amplifier device to choose fixed voltage output. When the amplifier device capacity small or radio coverage hours, depending on the situation to select fixed resistance output.
21.3.3 amplifier device capacity generally according to the following formula:
P=K1?K2?ΣP0
-P-amplifier device output total power (W)
P0-Ki? Pi, each tap simulcasting the maximum power consumption when
Pi – I slip road user equipment rated capacity
Ki – I tap at the same time need to factor:
Service broadcasting, the rooms show each Ki of 0.2 ~ 0.4
Background music system Ki of 0.5 ~ 0.6
Business of broadcast, the Ki of 0.7 ~ 0.8
Fire emergency broadcast, the Ki of 1.0 (simulcasting should be consistent with this specification relevant chapter 24)
K1-line attenuation compensation coefficient:
Line attenuation while taking 1.26 1dB
Line attenuation while taking 1.58 2dB
K2 – aging factor, generally take 1.2 ~ 1.4.
21.3.4 cable amplifier equipment should be set by power unit, the number of its standby shall be based on the degree of importance of broadcasting.
Standby power unit should be set to automatically or manually input links to important radio link, extra power unit should immediately.
21.3.5 civil buildings selected speakers in addition meet the sensitivity and directional frequency response, and other features and playback requirements, should satisfy the following requirements:
(1) Office, living room, rooms, etc., use 1 ~ 2W speaker box.
(2), corridor, entrance hall and public places of background music, business, radio, etc. 3 ~ 5W.
(3) in building decoration and interior height allowed on the premises used for large space sound columns (or combo box). (4) in noise is high, the humid place setting speaker, Horn loudspeakers should be used, their sound pressure level than the environment 10 ~ 15dB noise.
(5) outdoor speakers should be damp-proof protection.
21.3.8 in one to three-level Hotel background music speaker settings should satisfy the following requirements:
(1) speakers Centre spacing should be based on sound field of space in height, and the uniformity requirement, speaker directivity and other factors. Request high places, sound field uniformity is not appropriate to 6dB.
(2) under the public worship of noise, the speaker output, set the volume adjustment device in place; when a site is likely to double as a variety of purposes, the site's background music speakers tap install control switch.
(3) in combination with fire radio background music speakers, on-the-spot shall install volume control or control switch.
21.3.9 building speaker box Ming installed, the installation height is not lower than 2.2m (speaker bottom margin of the ground).
21.4.5 cablecasting control room of the signal cable should be used in shielding of cables and wear steel pipe. Pipe jacketing should receive protection.
21.5.1 building cable wiring should satisfy the following requirements:
(1) hotel room service of broadcasting channels use a twisted pair cable, other broadcasting channels use copper conductor stranded wire, plastic broadcasting channels need to wear a pipe or cable laying.
(2) different tap wire use different color difference of insulated wires.
21.5.2 outdoor broadcast line laying route and manner shall, in accordance with the General layout planning and professional requirements. When using direct in ground, should satisfy the following requirements:
(1) laying route should not be passed to reserve space or planning yet.
(2) in the laying of routing should avoid easy make cable damage, reducing and other pipeline crossing.
(3) buried cable laying in the green belt, when crossing the road, on the cross section should wear protective tube.