Public broadcasting and background music systems PA - Public Announcement

First, the system described

Broadcast audio system involves a wide range, from shopping malls, schools, hotels, railway stations, docks, squares to the venue, theaters, stadiums, etc. are all closely related thereto.

1.1

In the civil engineering design, broadcasting systems can be divided into the following categories:

A, for the public area (shopping centers, stations, terminals, shopping malls, restaurants, corridors, classrooms, etc.) and parking lots of the public broadcasting system.

This system is mainly used for voice broadcasting, so clarity is paramount. Moreover, such systems are often the usual background music broadcast in the event of disaster or emergency situations, but also converted to an emergency broadcast.

B, hotel rooms facing the broadcast sound system.

Such systems include room audio broadcasting and emergency broadcasts, often located in the rooms by the bedside cabinet run, room contains multiple radio bands for freedom of choice in an emergency broadcast, Room broadcast is automatically interrupted, automatically switches to emergency broadcasts.

C, with an auditorium, theater, stadium PA system as the representative hall.

This is a highly professional PA system, it should not only consider the electro-acoustic technology issues, but also issues related to architectural acoustics. Both must be balanced, can be neglected, such broadcasting system often requires an integrated multi-purpose venue not only for the use of language reinforcement, also commonly used in theatrical performances, live performance for large sound system, electric power ranging from tens of thousands, many hundreds of thousands of watts, so the use of high-power speakers and amplifiers, in the configuration and equipment selected aspects of the system have certain requirements, but should pay attention to the problem of electricity load line.

D, for conference rooms, lecture halls and other broadcast sound system.

Such systems are generally set to background music and emergency broadcasting public broadcasting system provides dual, but it is also because of the special nature often set up in a conference room and lecture hall meeting broadcast system separately. To require a higher or international conference hall, the need to be designed as a dedicated audio system simultaneous interpretation system, conference voting system and large-screen projection TVs and the like.

From the above description shows that, for a variety of buildings, hotels and other commercial buildings broadcast sound system, basically can be summarized into three types:

First, when the public address system (Public Address System abbreviated PA), which is the cable broadcasting system, which includes background music and emergency broadcast function, usually together, usually playing background music or other programs, fire and other emergency occurs, the conversion alarm broadcasts. This system broadcast to the public with a microphone and speakers generally do not broadcast at the same room, so silent feedback problems and constant pressure for a typical transmission system;

Second, sound reinforcement systems that use professional audio equipment, and requires a high-powered speaker system and amplifier, as the microphone and speaker with the same sound in a living room, so there is the problem of acoustic feedback and even howling, and because the distance is shorter, so the system generally use low resistance direct transmission;

The third is dedicated conferencing system, although it is also an amplification system, but has its own special requirements, such as simultaneous interpretation system.

1.2

Broadcast sound system consisting of

A broadcast audio system, can be substantially divided into four parts: source device, a signal amplification and processing device, the transmission line and speaker system.

Source Device: program source is usually radio, CD player and recording decks and other devices, in addition to the microphone, electronic musical instruments.

Signal amplification and processing equipment: including mixer, preamplifier, power amplifier and a variety of controllers and audio processing equipment. The primary task of this part of the device is the signal amplification, followed by the selection signal. Mixer and preamp role and status similar to (of course, the mixer features and higher performance), their basic function is to complete the selection and pre-amplified signal, in addition to Tanzania negative volume and variety of sound effects adjustment and control. Sometimes, in order to better balance and tone frequency beautification, but also separately invested graphic equalizer. This section is the "control center" of the entire broadcast sound system. PA amplifier or mixer will be sent a signal pre-power amplifier, and then to push through a transmission line speaker aloud. Transmission line is simple, but with different transmission methods and systems have different requirements. For auditorium, theater, etc., due to the distance of the power amplifier and the speakers far, the general way of direct fed low resistance high current, transmission line speaker wire with special requirements, while public broadcasting system, because a wide service area, long distance, in order to reduce loss caused by the transmission line, often using high-pressure transmission, due to the transport current is small, it is less demanding on the transmission line. Speaker System: Speaker System requirements throughout the system to match, but also to choose their location realistic. Auditorium, theater, dance hall sound, high quality requirements, and speakers generally use high-power speakers; while public broadcasting system, because of its timbre requirements are not so high, generally with 3W

-6W ceiling speaker that is good.

1.3

Features broadcasting system

Background music for short BGM, Back Ground Music is an abbreviation, its main role is to cover up the noise and create a relaxed and harmonious atmosphere, listening intently listening to people if not, we can not identify its source location, the volume is small, is a species can create a pleasant atmosphere of the music. Therefore, the effect of background music are the two psychological conceal ambient noise, and the second is to create the atmosphere of the indoor environment to adapt, it is widely used in guesthouses, hotels, restaurants, shopping malls, hospitals, office buildings and so on. Songs should be relaxed or lyrical style, strongly stimulated sexual music is inappropriate. Background music is not stereo, but mono music, which is required because of a stereo sound source can distinguish between orientation and feeling of depth, while the background music is not listening to the voice on unaware of where they come from, do not want people feel the location of the sound source, as well as the requirements of the concealed sound source, and the volume to be light, so as not to affect the two opposite speech principle.

1.4

Features fire radio function

Fire radio is enabled (it is closely related with the personal safety) and thus fire radio when there is an incident in

The following features ¦Ÿ

Fire alarm signal should have the highest priority in the system, you can find background music and call people and other states have a cut-off function.

¡î duty fire alarm should be easy to operate.

¡î transmission cables and speaker should have fire safety features.

¡î In the case of an AC power failure alarm should also ensure that broadcasts.

Second, the general order of public broadcasting engineering

Talking about here is the voice of public radio broadcasting cable transmission, usually used in shopping malls, public venues, buildings, within the cell, the background music for radio, radio paging and forced into a disastrous broadcasting. This kind of public broadcasting engineering design, usually in the following order:

1 should first consider using radio speaker configuration

2 optional radio power amplifier

3. Broadcast partition

Third, the radio speaker selection and configuration

1 should be chosen depending on the environment of different varieties and specifications of the radio speaker radio speaker selection principles.

For example, there is a ceiling on the ceiling of the room, to use embedded, no rear cover ceiling speakers. Such a simple speaker structure, relatively cheap, and easy construction. The main disadvantage is that there is no rear cover, susceptible insects, rodents bite. In the framework of the ceiling without ceiling only indoor (such as open-frame mall), it is appropriate ceiling-mounted speakers or tube-type rear cover ceiling speakers. Since a ceiling equivalent infinite baffle, so under conditions of use without the ceiling speaker cover does not cause a short circuit sound. The situation is quite different when there is no ceiling if still with no rear cover ceiling speakers, the effect will be poor. Then lifting the speaker should be used in principle. However, if too large investment, there can also be a ceiling speaker back cover. Ceiling speakers have a rear shield cover not only the general role of mechanical protection, but also serves to prevent short-circuiting of the sound effects to some extent. No ceiling in the room (such as an underground parking lot), are advised to use the indoor wall-mounted speakers or frets. Outdoors, should use the outdoor frets or horn. Such frets and horn function not only rain, but the volume is large.

Due to open outdoor environment, no reverb effect, choose a larger volume variety is a must. In the garden, lawn, should use

Lawn speaker. Such speakers rain, sleek, and the volume and sound quality are more particular about. In fitting stress, high ceiling hall wide, should use elegant, harmonious tones lifting speakers. Fire protection requirements in high places, should use fire-speakers. Such speakers are sealed type, the outlet port can be connected with the fire-retardant casing.

2 radio speaker configuration

The radio speakers uniform principle, the principle of decentralized configuration of the broadcast service area. The degree of dispersion of the signal to noise ratio should ensure that the service area is not less than 15dB. Typically, the noise floor office buildings corridor is about 48 ~ 52dB, the noise floor supermarket about 58 ~ 63dB, the noise floor of the downtown section of about 70 ~ 75dB. Consider the case of an accident, the scene can be very confusing, so in order to require emergency broadcasts, even if the broadcast service area is the office, nor should the background noise estimate is too low. Noted that, as a general consideration, in addition to bustling place, it may be generally regarded as the background noise (except in exceptional circumstances) 65 ~ 70dB. Same projections, SPL broadcast coverage area should be at 80 ~ 85dB or more. Given the configuration of radio speakers are usually scattered, so SPL broadcast coverage area can be considered a contribution of approximately a single broadcast speakers. According to LM SPL SPL sensitivity level electric acoustic theory related speaker coverage area with speakers, electric power is fed to the speaker P, with speakers from the listening point r and so have the following relationship:

SPL = LM +10 lgP-20lgrdB (1)

Ceiling speaker sensitivity level between 88 ~ 93dB; rated power of 3 ~ 10W. In 90dB/8W calculations, 8maway from the speaker at the SPL about 81dB. The above calculations contribution to the group's early reflections are not considered. Contribution in the room, early reflections groups and neighboring speakers SPL can increase by about 2 ~ 3dB. Based on the above approximation, the ceiling is not higher than3m

Inside the stadium, ceiling speakers can be roughly uniform distance from each other 5 ~8mconfiguration. If we consider only the background music, regardless of the emergency broadcast, the distance can be increased to 8 ~12m. In addition, suitable for Chinese mainland broadcast design and installation of fire norms (hereinafter referred to as the "Code") has the following mandatory: "aisles, halls, restaurants and other public places, configure the number of speakers, shall be guaranteed from any part of the floor to recently a walking distance from the speaker does not exceed15m. in the aisles at the intersection, the corner of the speakers should be located. aisle end of the last speaker from the wall no more than8m". Outdoor places virtually no early reflections group, effective coverage speaker can only take a single broadcast limit calculations above. As the lower limit corresponding to a short distance, it should be used by a plurality of loudspeakers fret in principle. Fed to the speaker group (for example, frets) signal for each doubling of electric power (provided that the group can accept), SPL enhance 3dB. Please note that the "doubling" of meaning. Is doubled from one to two; shall be from 2 to 4 and is doubled. In addition, the distance between each doubling the sound pressure level will drop

6dB. Configuration is easy to calculate the distance outdoor frets under such rules. For example, CS-540 outdoor frets example, the rated power of 40W, is more than four times the individual ceiling speakers. Therefore, the effective distance is greater than 2-fold coverage of individual ceiling speakers. In fact, this distance can also be larger. Because of the sensitivity of frets higher than a single ceiling speaker (about high 3 ~ 6dB), while each additional 6dB, the distance can be doubled. That could cover the distance of 540 frets over20m. However, the relatively narrow radiation angle frets, valid only within its right in front of about 60 to 90 degrees (horizontal) or so. The calculation is still available (1).

Fourth, the radio amplifier selection

Unlike radio amplifier HI-FI amplifier. Its main feature is a 70V and 100V constant voltage output terminals. This is due to the broadcast line is usually quite long, must be reduced by the high voltage transmission line losses can. The most important indicator is the radio amplifier

Rated output power. How much should use the rated output power, subject to the total power radio speaker may be. For broadcasting system, as long as the total power radio speaker amplifier is less than or equal to the rated power, and the same voltage parameters, you can freely connected with, but considering the line loss, aging and other factors, the power should be properly left margin. Accordance with the 'specifications' requirements, the capacity of the power amplifier device (equivalent to the rated output power) should generally be calculated as follows:

P = K1 • K2 • ¦²P0 (2) P - total electric power output amplifier device (W) P0 - each branch (equivalent to partitions) simulcast maximum electric power P0 = Ki • Pi Pi - the i partition speaker rated capacity Ki - first i also need to partition coefficient: room service broadcasting programs, take 0.2 to 0.4 0.5 to 0.6 background music department of broadcasting services, take 0.7 to 0.8 fire radio, take 1.0 K1 - line attenuation compensation coefficient: 1.26 ~

1.58K2- the aging factor: 1.2 to 1.4 noted that, if the background music systems, radio amplifier rated output power should be about 1.3 times the total power of the radio speakers. However, all public broadcasting system should in principle be able to make an emergency broadcast disasters. Therefore, the system shall be provided with an emergency radio amplifier. According to "standard" requirement, emergency radio amplifier rated output power shall be the maximum capacity of the three radio speaker speaker 1.5 times the capacity of the partition sum.

Fifth, broadcast partition

A public broadcasting system is usually divided into several areas, from the management (or pre-programmed) to decide which area shall be published broadcast, broadcasting to be suspended in those areas, those areas should be inserted into the emergency broadcast, "" and so on. Partitioning scheme in principle, depending on customer needs. Usually refer to the following rules:

1 floor building usually partitions, shopping malls, playgrounds usually zoning department, sports stadiums usually stands partition,

Residential district, residential quarters, resorts usually by Property Management Division, and so on.

2 administrations and public places should be divided into districts, respectively.

3 key sectors or broadcast by the speaker volume is necessary for field personnel should be adjusted individually districts.

In short, in order to facilitate the management partition. Those who need to be treated separately in the section should be divided into different zones. However, the total power of each area, the radio speaker is not too large, subject to the same partition and amplifier capacity to adapt.

Sixth, the public broadcasting system architecture shopping mall public address system architecture consists of four components: radio amplifier, audio input /

Out aloud equipment, intelligent player. The four organic tightly integrated into a unified public broadcasting system, the structure is designed to fully take into account the functional needs of the mall, but also pay attention to the construction costs of the system.