The Public Address (PA) is a system that is managed by the user to conduct business and emergency broadcasts for the public and provide background music within the scope of the building. At present, public broadcasting shows a good momentum of development. Mainly manifested in: more and more market demand, more and more complex functional requirements; the ability of broadcasting production enterprises to continue to improve, products are more and more human.
Today, with the rapid development of technology, public broadcasting and professional sound reinforcement systems in the same category of electro-acoustic have been greatly developed, but their development process has different characteristics: professional sound reinforcement systems are generally classified according to electroacoustic performance indicators, and public The broadcast is mainly graded according to the function of the preparation and the intelligibility of the language. In recent years, public broadcasting systems have shown a new trend of development in networking, wireless and high definition.
1. The development trend of public broadcasting network
There are many recent signs that public broadcasting has entered the era of networking.
A typical networked broadcasting system is an audio sound reinforcement system based on IP data network transmission. It can be used in the LAN of the same network segment, in the LAN of the gateway or on the Internet, and integrated into the TCP/IP networked broadcasting system based on the DSPPA protocol. It is an application that is more flexible than the broadcast system dedicated to the CobraNet private network. The CobraNet network broadcast system is a network audio real-time transmission technology that integrates hardware, software and communication protocols. It can guarantee the audio transmission quality, but it is limited by expensive equipment and cumbersome dedicated lines. A typical networked broadcast system consists of a network broadcast control center, a network terminal, a network paging microphone, and a network fire interface. The system breaks through the shortcomings of traditional public broadcasting that can only be transmitted down and can only be controlled centrally by the computer room. The interactive function is strong, and the partitioning and grouping can be arbitrarily combined and controlled, and the ultra-long-distance transmission can be realized through the network. If a typical networked broadcasting system is combined with a terminal system such as a safe city and a bank intercom, a special function expansion application can be realized.
Networked broadcasting systems are generally suitable for large-scale commercial buildings, schools (university cities), buildings, airports, stations, urban areas and other large areas. The Shanghai World Expo is a multi-level priority setting based on land parcels, districts, and national venues, which is cost-effective and easy to manage. The topology is shown in Figure 1 and Figure 2. At present, the standards for public broadcasting are mainly the "Public Broadcasting System Engineering Technical Specification" GB50526-2010 edited by the China Electronics Society Audio Engineering Branch and Guangzhou Disip Audio Technology Co., Ltd., and there is no standard for networked public broadcasting at home and abroad. And specifications.
There are a few things to note when designing a networked broadcast:
(1) It is necessary to understand the needs of users and avoid using networked public broadcasting for digitization and waste investment;
(2) Understand the design parameters of the network system to be built in the project, and judge whether the CobraNet network with high sound quality guarantee is a convenient, low-cost TCP/IP networking, and determine the multicast protocol to be opened;
(3) According to the project situation, prioritize and flexibly set up according to the requirements.
Figure 1 Shanghai World Expo master control room and network connection topology
Figure 2 Topology diagram of the computer room and network connection in the Shanghai World Expo area
2, the emergence of wireless broadcasting
In the "Eleventh Five-Year Plan" National Emergency Response System Construction Plan, it is proposed: "Strengthen the construction of early warning system and early warning information release platform, build public channels for public information release of public emergencies, and improve the whole society, especially in remote mountainous areas. Early warning capabilities at the end of information such as rural areas, to solve the bottleneck problem of the last one kilometer of warning information. The country attaches great importance to this piece of broadcasting system application. For this reason, the release of wired "ç¾ç»Š" radio broadcasting needs to be born.
In the past, a number of provinces have carried out some useful explorations in the “Village Village†and “Village Village†projects, with many valuable experiences and success stories. The existing broadcasting platforms, including cable TV and FM radio technologies, are mature enough to fully meet the application needs of rural emergency broadcasting. Rural broadcasting systems are used most of the time by grassroots, villages and other grassroots. The combination of the backbone network frequency modulation common cable transmission and the terminal wireless coverage can not only solve the problem of comprehensive coverage, but also realize multi-level linkage controllable and controllable. In the unlikely event of a major natural disaster such as the Wenchuan earthquake, FM radio technology will ultimately be effective. The backbone network can save investment by using the original radio and television network as much as possible, without additional line maintenance, saving resources and post-cost.
The role played by wireless broadcasting in combating natural disasters is irreplaceable, and it can quickly evacuate and direct disaster relief work. Due to the maturity of the technology and the moderate difficulty, there are also a few extensions or adaptations of wireless broadcasting systems.
The “village to village†system in a county in Sichuan Province is a typical case of a wireless broadcasting system. The design is simple, advanced, stable and reliable. It has completed multi-level addressable linkage function without using a large number of equipments, and has the ability to be compatible with county, township and village levels. Using the county-level radio station platform, the multi-function control host is the center, and various signals such as radio station signals, emergency radio microphone signals, GSM wireless networks, and telecommunication lines are entered into the emergency control host, and the priority levels of various signals are set. Hierarchical priority control. It pre-sets the telephone numbers of various government departments to the emergency control host and sets their own independent passwords. When an emergency broadcast needs to be released, you only need to dial the mobile phone number or wired phone number in the emergency control host to implement related operations according to the Chinese voice prompt content. The choice of partition can be achieved by telephone broadcast, direct broadcast voice or alarm signal, and a preset event can be executed. In the broadcast machine room, the control panel can directly control the partition selection and some main functions of the emergency control host. The topology is shown in Figure 3.
Figure 3 County-level broadcast transmission control system of a village in Sichuan Province
All towns and towns use wireless FM transmission to transmit signals to various administrative villages. Mainly based on a broadcast multi-function controller, the emergency broadcast signal from the county level is taken out from the closed-circuit television system, the signal from the emergency microphone, the external CD/DVD audio signal, the computer audio signal and the control data signal, the GSM mobile phone receiving signal, etc. All are sent to the multi-function controller. Through the mixing of the internal hardware of the controller and the prioritization of the program. The audio signal and the control signal are sent to the transmitter on the mountain through a dedicated audio optical transceiver, and finally reach the administrative village through the transmitting antenna. See Figure 4.
Figure 4 Wireless broadcasting system in the villages and towns of a county in Sichuan Province
Figure 5 Broadcasting system of “Village Village†administrative village in a county of Sichuan Province
The administrative village has a local broadcasting function and can also receive emergency broadcast signals from townships and counties. As shown in Figure 5, the system is relatively simple in structure. It is centered on an addressable broadcast control terminal and has a 120W constant voltage amplifier. It can connect four 25W high-definition horn speakers at the same time. Usually broadcast daily broadcasts, when the superior has an emergency broadcast release, it automatically switches to receive the broadcast broadcast of the superior. At the same time, the system is equipped with a set of UPS power supply, which can perform long-term emergency broadcast even if the mains is stopped.
Jiangxi Province is located in the East Asian monsoon region. The terrain and geological conditions are complex. The special climatic conditions and the spatial and temporal distribution of precipitation are uneven. It is easy to form local heavy rainfall, which leads to frequent mountain torrent disasters. Many counties in the province are included in the county-level non-engineering of mountain torrent disaster prevention. Construction of measures. Mountain-level disaster prevention and control County-level non-engineering measures are built to establish existing storm flood monitoring systems, information transmission and reception systems, early warning information service systems, rural terminal early warning systems and group monitoring and prevention systems to cover existing mountain flood disasters. The defense system effectively mitigates the losses caused by mountain torrents. According to the design, the village committee of the mountain flood disaster-prone area will build a radio broadcasting main station, and the natural villages and groups under its jurisdiction will build a radio broadcasting substation. The primary station can receive the warning information transmitted by the early warning center, send it to the early warning area sub-station through the radio broadcast main station, and broadcast it to each household with a tweeter. As shown in Figure 6.
Figure 6 Topography of the wireless broadcasting early warning system in Jiangxi Province
3. Development trend of high-definition broadcasting system
For a long time, the sound reinforcement of the broadcasting system of the railway station has been poorly defined, and it is unclear when people are noisy. With the rapid development of railway technology, the requirements for railway transportation equipment for railway transportation are getting higher and higher. The original broadcasting system can not meet the new requirements. Take the Hankou Railway Station broadcasting system as an example. The main performances are as follows:
The ceiling/wall/floor/column is not treated with sound absorption;
Space volume in the station: 138m (L) × 64 m (W) × 18 m (H);
The reverberation time is up to 7.6S, and the 200Hz standing wave is severe;
The ambient noise is as high as 75dB when there are passengers.
In such a complicated sound-building environment, broadcast sound reinforcement has been unsatisfactory. The relevant leaders of the Ministry of Railways believe that it is necessary to improve the sound reinforcement application of the broadcasting system at the station to achieve high-definition requirements.
Defining the clarity of the sound reinforcement system is the Sound Transfer System Language Transmission Index (STIPA), which is clearly explained in the Public Technical System Technical Specification 2.0.29: STIPA is a simplified form of the language transmission index. Objectively evaluate the language transmission quality of sound reinforcement systems (including public address systems). The public address acoustic performance indicators of all levels are listed in 3.3.1. STIPA can be measured by related instruments. Figure 7 shows that the STIPA value defining the sound reinforcement HD must be greater than or equal to 0.80.
Figure 7 shows the STIPA value of the clarity of the sound reinforcement
In response to the reality of high-definition demand, well-known manufacturers have developed strong directional, high-power, high-band sensitivity, slow-band attenuation, and high-definition (STIPA up to 0.88) remote ceiling speakers or HD in single speakers and speakers. The remote horn speaker, combined with the narrow frame and streamlined appearance of the cabinet, can meet the requirements of high requirements and bring high-definition sound experience. In some public halls of halls and exhibitions, there are small (micro) line array speakers and flat line array speakers as shown in Figure 8. These products have high sensitivity, direct sound intensity, and easy construction. installation.
Figure 8 Small line array speakers and flat line array speakers that have appeared in recent years
Another way to achieve high-definition sound reinforcement is phased array technology, where Chinese broadcast technology is unique. As shown in Figure 9, the phased array sound column uses digital processing technology (DSP) to virtualize the directional characteristics of different shaped sound columns, and the other properties of the sound column itself are not affected, which is suitable for poor acoustical conditions of buildings [large volume, The halls and stadiums with poor sound conditions, long reverberation time and turbid sound are amplified, and remotely controlled by a remote control or computer to achieve accurate coverage of the sound area (audience seats, etc.) and to prevent it from spreading to useless areas. Reduce the acoustic investment in stadiums and the energy consumption of sound reinforcement systems.
Figure 9 Phased array sound column realistic sound field performance
Phased array speakers have been widely used, such as the Xinjiang Karamay Convention and Exhibition Center exhibition hall equipped with flat line array speaker; Guangdong Science Center uses phased array sound column to perfectly adapt to the complex environment of building sound and so on.
4 Conclusion
The trend of public broadcasting showing network, wireless and high definition is the result of the common demand of market demand and technology development, which also promotes the development of public broadcasting technology in our country.
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