The current development situation of BGMPA

In today's fastchanging technology, public broadcasting and professional sound reinforcement systems, which belong to the same electroacoustic category, have been developed significantly, but their development process has different characteristics: professional sound reinforcement systems are generally graded according to electroacoustic performance indicators, while public broadcasting is mainly graded according to the available functions and language intelligibility. In recent years, the public broadcasting system has shown a new trend of network, wireless and HD development.

    1、Network development trend of public broadcasting

    Recently, many signs show that public broadcasting has entered the era of networking.

    A typical networked broadcasting system is an audio PA system based on IP data network transmission, which can be used in the LAN of the same network segment, cross-gateway LAN or Internet network. Networked broadcast system is a real-time network audio transmission technology integrating hardware, software and communication protocols, which can guarantee audio transmission quality, but is limited by expensive equipment and cumbersome dedicated lines, and is not flexible enough. A typical networked broadcast system is composed of network broadcast control center, network terminal, network paging microphone, network fire interface, etc. The system breaks through the shortcomings of traditional public broadcasting which can only be transmitted down and controlled centrally by the server room, with strong interactive function, and the combination of partition and grouping can be manipulated at will, and ultra-long distance transmission can be realized through the network. If the typical networked broadcasting system combined with safe city and bank intercom and other terminal systems can realize special function expansion applications.

    Networked broadcasting system is generally applicable to large commercial buildings, schools (university cities), building clusters, airports, stations, city districts and other large area occasions. The Shanghai World Expo is using the networked broadcasting system to set multi-level priority by parcel, area, and national venue, thus saving cost and managing easily. At present, the standard of public broadcasting is still mainly the "Public Broadcasting System Engineering Technical Specification" GB50526-2010 compiled by the Sound and Frequency Engineering Branch of the Chinese Institute of Electronics, and there are no standards and specifications specifically for networked public broadcasting at home and abroad.

    The design of networked broadcasting requires attention to several points.

    (1) Should be a practical understanding of the needs of the user, to avoid the use of networked public broadcasting for the sake of digitalization, wasting investment.

    (2) Understanding the design parameters of the network system to be built for the project, judging whether the CobraNet network with high quality assurance or the convenient and low-cost TCP/IP networking should be used, determining the multicast protocol to be opened, etc.

    (3) According to the project situation set priorities according to the demand hierarchy, flexible networking.

  2、Wireless broadcast emergence

    The "Eleventh Five-Year Plan" national emergency response system construction planning: "strengthen the construction of early warning systems and early warning information dissemination platform, build all kinds of public emergency information dissemination channels, improve the whole society, especially the remote mountainous areas, rural areas and other information end of the early warning capability. Solve the bottleneck problem of the last kilometer of early warning information dissemination". The country attaches great importance to this piece of broadcasting system applications, for this reason, lifting the wired "tie" wireless radio should be born.

    Previously, several provinces in the "village pass" and "village sound" project, some useful exploration, with a lot of valuable experience and success stories. The existing broadcasting platforms, including cable TV and FM radio, are technically mature and fully capable of meeting the application needs of rural emergency broadcasting. The rural broadcasting system is used by the grassroots level such as towns and villages most of the time. The combination of backbone network FM common cable transmission and terminal wireless coverage can not only solve the problem of comprehensive coverage, but also realize multi-level linkage that can be managed and controlled. In case of a natural disaster such as the Wenchuan earthquake, the ultimate effective or FM broadcast technology. 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 later costs.

    The role of wireless broadcasting in the fight against natural disasters is irreplaceable, can quickly evacuate, command disaster relief work. Due to the mature technology and medium difficulty, wireless broadcasting system extension or adaptation application is not few.

    A county in Sichuan Province "village pass" system is a typical case of wireless broadcasting system. The design is simple, advanced, stable and reliable, and the multi-level addressable linkage function is completed without using a large amount of equipment, with the ability to be compatible with county, township and village linkage. Using the county radio station platform, the multi-functional control host as the center, the radio station signal, emergency broadcast microphone signal, GSM wireless network, telecommunication lines and other types of signals into the emergency control host, by setting the priority level of various types of signals to achieve a hierarchical priority control. It pre-sets the phone numbers of various government departments into the emergency control host and sets their independent passwords. When you need to release emergency broadcast, you only need to dial the cell phone number or wired phone number in the emergency control host, and you can realize the relevant operation according to the content of Chinese voice prompt. Through telephone broadcasting can realize the choice of partition, directly broadcast voice or issue alarm signal to execute a preset event. The partition selection and some main functions of the emergency control host can be directly controlled by the control computer in the broadcasting room.

    Each township uses wireless FM transmission to transmit signals to each administrative village. With one broadcast multi-function controller as the main unit, emergency broadcast signals from the county level taken out from the closed circuit TV system, signals from the emergency microphone, external CD/DVD audio signals, computer audio signals and control data signals, GSM cell phone reception and other signals are all sent to the multi-function controller. After the controller internal hardware mixing and program priority ranking processing. The audio signal and control signal are sent to the transmitter on the high mountain through the special audio optical transceiver, and finally reach each administrative village through the transmitting antenna.

    The administrative villages have the function of local broadcasting and can also receive the emergency broadcasting signals from the township and county. The composition of the system is relatively simple, with an addressable broadcast terminal as the center, with its own 120W fixed-voltage amplifier, which can be connected to four 25W high-definition horn speakers at the same time. Normally, the daily broadcast is released locally, and when there is an emergency broadcast released at the higher level, it automatically turns to receive the broadcast signal from the higher level. At the same time, the system is equipped with a set of UPS power supply, even if the utility power is stopped, it can also carry out long-time emergency broadcasting.

    Jiangxi Province is located in the East Asian monsoon region, with complex topographic and geological conditions, special climatic conditions and uneven spatial and temporal distribution of precipitation, which makes it very easy to form local heavy rainfall, resulting in frequent flash floods. The construction of county-level non-engineering measures for flash flood disaster prevention and control is to improve the existing flash flood disaster defense system and effectively reduce the losses caused by flash floods by establishing a storm flood monitoring system, information transmission and reception system, early warning information service system, village end early warning system and group measurement and prevention system covering flash flood-prone areas. According to the design, the main wireless broadcasting station is built in the village committee of the flash flood-prone area, and the natural villages and groups under its jurisdiction build wireless broadcasting substations. The main station can receive the early warning information transmitted by the early warning center, send it to the sub-station in the early warning area through the main wireless broadcasting station, and broadcast it to each household by tannoy.

        3、The development trend of broadcasting system HD

    For a long time, the broadcast system of railway station has poor sound amplification clarity, and it is hard to hear when there are many people and noisy. With the rapid development of railroad technology, railroad traffic requirements for railroad supporting equipment are also getting higher and higher. The original broadcasting system cannot meet the new requirements, taking Hankou Railway Station broadcasting system as an example, the main performance are.

    The roof/walls/floor/columns are not treated for sound absorption.

    The volume of station space:138m (L) × 64 m (W) × 18 m (H).

    Reverberation time up to 7.6S, with severe standing waves at 200Hz.

    The ambient noise is up to 75dB when there are passengers.

    With such a complex sound environment, the broadcast sound reinforcement has been unsatisfactory, and the relevant leaders of the Ministry of Railways consider it necessary to improve the broadcast system in the station sound reinforcement application to achieve high-definition requirements.

    To define the clarity of the sound reinforcement system is the sound reinforcement system language transmission index (STIPA), in the "Public Address System Engineering Technical Specification" 2.0.29 made a clear explanation: STIPA is a simplified form of language transmission index, used to objectively evaluate the quality of language transmission of the sound reinforcement system (including public address system). STIPA can be measured by relevant instruments. Figure 7 indicates that the STIPA value defining sound reinforcement HD must be greater than or equal to 0.80.

    In response to the realistic demand for HD, well-known manufacturers in the single horn, speaker developed a strong directivity, high power, full-band sensitivity, slow out-of-band decay speed, high language clarity (STIPA up to 0.88) remote ceiling speaker or HD remote horn speaker, coupled with the box narrow bezel, streamlined and other appearance modifications, can meet the high requirements of the occasion, bringing high-definition sound feeling. In some large halls, exhibition applications of public broadcasting, the emergence of small (micro) line array speakers and flat line array speakers, such products with high sensitivity, direct sound intensity effect is good, while extremely easy construction and installation.

Another way to achieve high-definition sound reinforcement is phased-array technology, China's broadcast technology is unique in this. Phased array sound column using digital processing technology (DSP) can virtual different shapes of sound column pointing characteristics, and the other properties of the sound column itself is not affected, suitable for building acoustic conditions poor [volume space, poor sound conditions, long reverberation time and sound turbidity] of the hall, stadium sound reinforcement, with remote control or computer remote control to achieve accurate sound coverage of useful areas [audience seats, etc.], and inhibit its Diffusion to useless areas, reduce the investment in acoustic decoration and sound reinforcement system energy consumption.

  Phased array speakers have been widely used, such as the exhibition hall of the Xinjiang Karamay Convention Center equipped with flat line array speakers; Guangdong Provincial Science Center using phased array sound column perfectly adapted to the complex environment of building sound and so on.