What Is a Public Address Amplifier?

Public broadcasting, also known as public broadcasting service or public media, refers to non-profit electronic media established and operated by the government to budget or provide funds from public funds. Such media are mostly used to produce and broadcast public policy discussions. The main purpose is cultural, educational arts or intellectual programs. The purpose is to improve the level of national knowledge and promote public participation in political decision-making. News media regulated by governments of non-democratic countries are generally not called public media. Although this type of TV station is also supported by government funds, these media generally lack the independence of editing and operation, and the independence of broadcast content and operation Sex is an important symbol of public media. Because it is not for profit, most of the public media does not broadcast commercial advertisements. In addition to government funding, it also accepts donations from individuals or groups. In some countries, users are charged taxes and fees. In some places, in addition to television broadcasts, public media also provide radio and Internet services.

Public broadcasting

1. The public broadcasting system can be divided into the following categories according to the transmission and signal processing methods:
No matter what kind of broadcasting sound system, it can basically be divided into four parts as shown in Figure 1: program source equipment, signal amplification processing equipment, transmission line and speaker system .
The intelligentization of public broadcasting requires the system to be capable of timing sound sources, power supplies, partitions, and linkage with fire broadcasts, so there are also timers, program timing players, power sequencers, audio matrixes, central control hosts, fire collectors, etc.
Appendix: National Standards
There are many specific regulations on the design and installation of cable broadcasting and accident broadcasting in the "Code for Electrical Design of Civil Buildings" (JGJ / T16-92) issued by the Ministry of Construction of the People's Republic of China in 1993. The following are excerpts for design and daily management Reference:
twenty one. Cable broadcasting
21.1.1 Public buildings shall be provided with a line broadcasting system. The type of system should be determined based on the size of the building, the nature of its use, and its functional requirements. Cable broadcasting can be generally divided into:
Operational broadcasting system.
Service broadcasting system.
(3) Fire accident broadcasting system.
21.1.2. Business buildings, such as office buildings, commercial buildings, colleges, stations, passenger terminals, and airports, shall be provided with business broadcasts to meet the requirements of language broadcasts mainly for business and administrative management. Commercial broadcasting should be managed by the competent authority.
21.1.3 Class 1 to 3 hotels and large public event venues should have service broadcasts to meet the requirements of listening music broadcasts. Hotel service radio programs should not exceed five sets.
21.2.4 The line attenuation from the output end of the power amplifier equipment to the farthest user speaker box on the line should meet the following requirements:
Service broadcasting should not be greater than 2dB (at 1000Hz).
Service broadcasting should not be greater than 1dB (at 1000Hz).
21.2.6 For feed lines with constant voltage output, the output voltage should be 70V or 100V.
21.2.8 When the program signal and the telephone line are combined with one cable, the propagation level of the program signal should not be greater than 7.8dB. When the number of program signal lines is large, special cables should be used.
21.3.2 The power amplifier equipment of cable broadcasting should choose constant voltage output. When the capacity of the power amplifier equipment is small or the broadcast range is small, the fixed resistance output can also be selected according to the situation.
21.3.3 The capacity of power amplifier equipment is generally calculated according to the following formula:
P = K1 K2 P0
Where Pthe total output power of the power amplifier equipment (W)
P0Ki? Pi, maximum electric power when each branch is broadcasting at the same time
Pirated capacity of user equipment in the i branch
KiThe coefficient of the ith branch is needed at the same time:
For service broadcasting, 0.2 ~ 0.4 per Ki for each room program
Background music system Ki takes 0.5 ~ 0.6
For business broadcasting, Ki takes 0.7 ~ 0.8
When broadcasting a fire accident, Ki shall be 1.0 (while the broadcasting scope shall comply with the relevant provisions in Chapter 24 of this specification)
K1line attenuation compensation coefficient:
Take 1.26 at 1dB line loss
Take 1.58 when the line loss is 2dB
K2Aging factor, generally taken 1.2 ~ 1.4.
21.3.4 The cable broadcast power amplifier equipment shall be provided with a backup power unit, and its backup quantity shall be determined according to the importance of broadcasting.
The standby power unit should be provided with automatic or manual input links for important broadcast links, and the standby power unit should be immediately switched on.
21.3.5 In addition to the requirements for the characteristics of sensitivity, frequency response, directivity, and playback effects, speakers used in civil buildings should meet the following requirements:
1 ~ 2W speaker box can be used in offices, living rooms, guest rooms, etc.
3 ~ 5W for background music, business broadcasting, etc. in corridors, hallways and public event venues.
(3) Where the building decoration and indoor clear height allow, the sound column (or combination speaker) should be used in the large space. When setting up speakers in a place with high noise and humidity, use a horn speaker, and its sound pressure level should be 10 ~ 15dB greater than the ambient noise.
Outdoor speakers should be protected against moisture.
21.3.8 The setting of background music speakers in first- and third-level hotels should meet the following requirements:
The center distance of the speakers should be determined based on factors such as the clear space of the space, the sound field and uniformity requirements, and the directivity of the speakers. In places with high requirements, the unevenness of the sound field should not be 6dB.
According to the noise of public places, the volume of the speakers should be set on the spot. When a venue may be used for multiple purposes, the switch of the background music speakers in the place should be installed.
(3) The background music speakers used in conjunction with the broadcast of fire accidents must not be equipped with volume adjustment or control switches at the scene.
21.3.9 When the speaker box in a building is surface-mounted, the installation height should not be lower than 2.2m (the bottom edge of the speaker box is away from the ground).
21.4.5 The various program signal lines of the cable broadcast control room shall be shielded and run through steel pipes. The outer sheath of the pipe should be connected to the protective ground wire.
21.5.1 The cable broadcasting wiring in a building shall meet the following requirements:
The service broadcasting lines of hotel rooms should use twisted pair cables, and other broadcasting lines should use copper-core plastic twisted wires. The broadcasting lines should be laid through pipes or trunking.
The wires of different shunts should be distinguished by insulated wires of different colors.
21.5.2 The laying route and method of outdoor broadcasting lines shall be determined according to the general plan and professional requirements. When laying underground, it shall meet the following requirements:
Buried routes should not pass through reserved land or unplanned sites.
Buried routes should avoid places that are prone to cable damage and reduce crossovers with other pipelines.
(3) The buried cable should be laid under the green belt. When crossing the road, the crossing section should be protected by steel pipes.
The history of the public broadcasting system is actually very long, and we wo nt talk about it too far. Take modern times for example. Before the reform and opening up, the public broadcasting system had widely existed in the vast rural areas of mainland China, as well as troops, institutions, schools, factories and enterprises Among them, it is mainly used to relay news, announcements and work and rest signals from the central government and government at all levels.
In rural areas, the most typical is the public broadcasting system managed by the commune broadcasting station. The "talk box" of each household is the terminal of these systems. In the army and towns, various units have broadcasting rooms and are hung everywhere. Raising the horn. 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 has played a huge role in educating the masses, mobilizing the masses, issuing government orders, and mobilizing and organizing the masses. The establishment of so many public broadcasting networks on the vast land of China is a very great project. Not only is the investment huge, but it has also trained a large number of engineering and technical personnel, which has greatly promoted the domestic telecommunications and electro-acoustic industries. development of.
Due to the limitation of economic and technological development levels, the public broadcasting systems scattered throughout mainland China before the reform and opening up were basically the simplest systems. They formed a nationwide and very large network of downloads through the Central People's Broadcasting Station. However, technically, its functions are very limited, mainly voice broadcasts that are uniformly gated throughout the network. Broadcasting equipment is simple, economical and practical.
Since the reform and opening up, due to economic development and technological progress, in terms of public broadcasting, both domestically and internationally, the situation has changed a lot.
1. Due to the many channels of modern information, the function of public broadcasting networks for publishing general news and government orders has gradually diminished (especially in urban areas); simple, centralized, unified, and common public broadcasting networks have gradually become Individual, diverse and versatile stand-alone systems.
2. The system's quality index has specifications and new pursuits, and the requirements have been greatly improved than in the past. To put it simply, the previous public broadcasting only required that the voice from the "talk box" be audible (to be able to distinguish what it said), and there were no other quantitative specifications. There are standards for the signal-to-noise ratio, power, frequency response, and distortion of the system. The state has strengthened the market access system for electronics, electrical appliances and other products. In order to ensure the safety of use and necessary electromagnetic compatibility characteristics, as a new requirement for quality indicators, the main equipment of public broadcasting systems must pass 3C certification. This situation deserves the attention of the industry.
3. Every new or old unit needs to have its own public broadcasting system. The pattern has not changed, and systems such as emergency broadcasting are even mandatory and must be established. With the development and progress of economy and technology, the old system needs to be updated, and the new system needs to be established.
4. Minimize the system
Compared with the simplest systems in the past, the "minimum system" mainly adds the zone link, timing control link, alarm link and the interface with the fire center. In normal times, the system runs automatically under the management of a programmable timer. It regularly turns on and off the power of the relevant link according to a pre-programmed program, automatically plays background music, and plays the clock signal at the right time on the schedule. When the fire center sends an alarm to the system, the relevant links are forcibly started through the linkage interface (regardless of the program state); at the same time, emergency broadcasts (including the closed broadcast area) are forcibly inserted. "Minimal system" is not only convenient but practical.
5.Typical system
The "minimum system" mentioned above is actually not the most complete system. It has two main disadvantages. One is that it cannot achieve "zone forced insertion", and the other is that it lacks the necessary reliability guarantee. The so-called "partition forcing" means that when it is necessary to insert an emergency broadcast (including paging) outside the normal procedure, some relevant partitions can be selected for "forcing" without disturbing the normal operation of unrelated partitions. "Fire alarm" is a typical example. When the fire is in its infancy, we only need to issue warnings to the fire area and the neighboring areas that are easily affected, and we should not alarm other unrelated areas to prevent the accident from expanding. As for the reliability problem, it is mainly considered that the reliability of the high-power electronic equipment (the power amplifier of this system) and the power grid cannot be reassured at the current stage. It is necessary to set up a backup link that can be automatically input to ensure that the system can be continuously run. In addition, there should be lightning protection facilities for outdoor broadcast lines. Compared with the smallest system, the typical system has added alarm matrix, zone forced insertion, zone paging, telephone interface and main / standby power amplifier switching, emergency power supply, lightning arrester and other links. The system connection has also been adjusted accordingly.
6. Matrix system
If you need to play different programs in different broadcast partitions at the same time, you should use a matrix system. The matrix system can be assigned to different broadcast partitions through the matrix partitioner. These program sources can be broadcast at the same time or at different times, run automatically by a programmable timer according to a pre-programmed program, or can be manually intervened at any time.
development trend
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 network.
The public address system (PA system for short) is widely used in stations, airports, hotels, commercial buildings, hospitals, and various buildings to provide background music and radio programs. In recent years, the public address system has doubled as an emergency broadcast. Its main uses are business propaganda and current affairs policy broadcasting, background music and public paging, emergency broadcasts of fire accidents and emergencies.
Today's public broadcasters integrate background music, publicity, paging broadcasts, and emergency broadcasts for fire accidents. This is a very versatile broadcasting system. This general public broadcasting system must have the following functions and technical requirements:
1.Play background music and play paging
Background music is called BGM (Back Ground Music) for short. Its role is to cover up the environmental noise of public places and create a relaxed and happy atmosphere. The average sound pressure of background music is around 60 to 70db.
When the paging broadcast is played in the background music, there should be a reminder such as a jingle or a bell to remind the public's attention.
2.Emergency broadcast
In the past, the emergency broadcast system was combined with the fire alarm system as an independent system. However, it was later discovered that the reliability of the emergency broadcast system has not become a problem for a long time. Usually it is no problem in normal tests, but it becomes dumb when it is officially used. Fire alarm system and background music
No background music playback in a single room
There are two reasons for the failure. First, find out whether the corresponding area of the room is playing background music. You can see whether the background music is playing through the background music source on the call station keyboard. If the background music is not playing, Select the corresponding background music for playback. If there is selection in the background music source area and single room cannot play background music, then check whether the volume control switch of the corresponding room is turned on. If the volume control switch is not turned on , Then turn on the volume control switch, the background music can play the background music, if the volume control switch is turned on and still cannot play the background music, please contact the relevant engineering construction unit for troubleshooting.
Can't play background music in all areas
Under the condition that the background music playback has been selected, the background music playback still cannot be performed. Please check whether all devices are powered normally. If the power supply is abnormal or the related devices are not powered, please power on the related devices. The background music cannot be played after the device is powered on normally. Please check whether a music disc is inserted in the source device. If not, please insert a music disc. If the disc is inserted and the source device also plays the disc, please contact the relevant The project construction unit shall troubleshoot the fault.
Suddenly no sound when playing background music
Please check whether the disc in the audio source device is finished playing. If the disc is finished playing, please replay it; if the disc is not played and stops playing, please remove the disc in the source device and check whether the disc has been damaged. The background music is playing or the sound is intermittent when you call manually, please contact the project construction unit
LAX (Ruifeng)
DongChuang ( )
3UNM (3U)
DTSAIC (Dieters)
CEO-PA (Western style)
HUSPA (Lake Sound)
Inter-m (sound bridge)
CTRLPA (Kenjo)
DEIBAN (Durban)
DISINCE (Emperor Star)
LS (Laishi)
BOSCH (Bosch)
NEBON, New York
OPLL (European)
POSITVE (Daiyang)
SONBS (Dr. Sheng)
SPXBPA (Sibon)
Tiks (Iron Jockey)
ZABKZ (Obike)


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