Since the natural sound source (such as speech, singing, instrumental performance, sound reproduction, etc.) emits very limited sound energy, its sound pressure level is attenuated as the propagation distance increases, and the influence of environmental noise makes the sound source The propagation distance is limited. Therefore, in public places, electronic technology, sound reinforcement system must be used for sound reinforcement, the sound source signal should be amplified, and the sound pressure level of the audience area should be improved to ensure that each listener can obtain the appropriate sound pressure level.
The public address system is a systematic project, which requires close cooperation with various disciplines such as electronic technology, electroacoustic technology, sound construction technology and acoustic art. The sound effect of the public address system is not only related to the comprehensive performance of the electroacoustic system, but also The sound propagation environment is closely related to building acoustics and live tuning. Therefore, the final effect of the public broadcasting system requires the correct and reasonable electroacoustic system design and debugging, good sound propagation conditions and the correct on-site tuning technology. The three complement each other indispensable. In the system design, we must comprehensively consider the above problems. On the basis of selecting electro-acoustic equipment with good performance, through careful system design, careful system debugging and good sound-building conditions, the electroacoustic and natural sound effects can be achieved.
The public address system includes background music and emergency broadcast functions, usually combined, and it is targeted at public places, installed in corridors, elevator doors, elevator cars, halls, shopping malls, restaurants, bars, banquet halls, community gardens, etc. Combined sound column or decentralized speaker box, usually play background music, when an emergency occurs, strong cut for emergency broadcast, use it to command evacuation. The public broadcasting system has many control functions, such as the selection broadcast and full call broadcast function, the forced switching function, and the priority broadcast function. The public address system has a large number of speaker loads and a long transmission line. In order to reduce the transmission line loss, 70V or 100V constant voltage and high impedance transmission are generally adopted . Sound pressure requirements are not high, and the sound quality is dominated by midrange and mid-high. The microphones used for broadcasting in such systems are generally not in the same room as the speakers that are broadcast to the public, so there is no problem of silent feedback.
The history of the public broadcasting system is actually very long. If we are too far away, we will not talk about it. Let’s take it for the modern era. Before the reform and opening up, the public broadcasting system has been widely distributed in the vast rural areas and troops, institutions, schools, factories and enterprises in mainland China. Among them, it is mainly used to broadcast news, announcements and work signals of the central government and various levels of government.
In the rural areas, the most typical one is the public broadcasting system managed by the commune broadcasting station. The " speaking scorpion " of each household is the terminal of these systems; in the troops and towns, all units have broadcasting rooms, which are hung everywhere. The horn is raised. It can be said that almost no unit in mainland China has no public broadcasting system, and its popularity is the highest in the world. This plays a huge role in educating the masses, mobilizing the masses, issuing decrees, launching and organizing the masses. It is a very great project to build such a large number of public broadcasting networks on the vast land of China. Not only is the investment huge, but it also cultivates a large number of engineers and technicians, which greatly promotes the domestic telecommunications and electro-acoustic industries. development of.
However, due to the limitations of economic and technological development level, the public broadcasting system scattered around mainland China before the reform and opening up is basically the simplest system. They form a nationally large number of passes through the Central People’s Broadcasting Station. The internet. However, technically, its functions are very limited, mainly due to the unified voice recording of the entire network. Broadcasting equipment is simple, economical and practical.
Technology is constantly improving and market demand is constantly changing. The new development of public broadcasting technology is mainly manifested in two aspects of intelligence and networking. Modern intelligent buildings require the establishment of data networks, video networks and audio networks. The public broadcasting network turns the traditional public broadcasting network into a data network, and connects various terminals such as the broadcasting terminal, the on-demand terminal, the sound source collection / paging terminal, and the remote control terminal, so that the installation and the control are convenient and flexible. Sharing resources in different places.
The so-called portable projector, also known as pocket projector, mainly through the 3M LCOS RGB three-color projector and decoding technology, the traditional huge projector is compact and portable, making the projection technology closer to life and entertainment.
Advantages compared with traditional projectors:
1. Small size, light weight, easy to carry.
2. Low calorific value and low noise.
3. The price is relatively cheap.
4. Most models support wireless connection through software projection.
Applicable fields:
1. Replace some functions of TV: some machines can have built-in CMMB function, or can be directly connected to the set-top box to put TV, which can be used as a 21-inch TV during the day and a 60-100-inch TV at night (Note: Because of lumen and resolution issues, lumens during the day If the degree is not enough, it must be projected at a close distance) to achieve the effect of home theater; it is convenient to move and break through the traditional film and television space. Even if you are on the mountain, you can also share today's TV series, movies, and MTV with your lover.
2. Business trip: Portable projectors are easy to carry because of their small size and light weight. When you need to display computer content or mobile phone content, you only need to connect the portable projector to achieve the demonstration effect.
3. Private space: For dormitory beds or small private spaces, in the absence of a computer, you can use a portable projector to project the content of your mobile phone to watch video pictures, etc., without staring at the mobile phone at close range.
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