Comprehensive Guide to Public Address Systems

Public address (PA) systems are commonly encountered in various projects such as office buildings, residential complexes, commercial office buildings, schools, hospitals, railway stations, airports, bus stations, banks, and factories. This guide will provide a detailed overview of PA systems.

1. Components of a PA System?

Regardless of the type of PA system, it generally consists of four main parts: source equipment, signal amplification and processing equipment, transmission lines, and speaker systems.

1. Source Equipment

Music Players: Used for background music. Microphones: Includes standard microphones and zone-select microphones. Voice Storage Devices: For storing business and emergency broadcast messages.

2. Signal Processing and Amplification Equipment

Audio Signal Processor: Handles audio signal compensation, attenuation, equalization, etc. Pre-Amplifier: Pre-amplifies audio signals. Power Amplifier: Amplifies audio signals to drive speakers, providing constant voltage output.

?3. Transmission Lines

The service management platform software permits the monitoring center to exert centralized governance over the broadcast and intercom communication systems. It facilitates live device status monitoring, fault diagnosis, and troubleshooting, solidifying system dependability and consistency.

4. Speakers

Ceiling Speakers: Indoor, flush-mounted in the ceiling, constant voltage or constant impedance. Wall-Mounted Speakers: Wall-mounted, constant voltage or constant impedance. Column Speakers: Free-standing, suitable for indoor or outdoor use. Horn Speakers: High sensitivity, suitable for indoor or outdoor use. Camouflaged Speakers: For outdoor settings like parks or gardens, designed to look like rocks, mushrooms, or stumps.

2. Audio Technical Specifications of PA Systems

In daily environments, typical sound pressure levels are: ? Office noise: 50-60 dB ? Normal conversation: 65-70 dB ? Textile factory noise: 110-120 dB ? Small caliber gunfire: 130-140 dB ? Large jet aircraft noise: 150-160 dB

1. Signal-to-Noise Ratio (SNR)

SNR measures the ratio of the signal voltage to noise voltage, expressed in decibels. A higher SNR indicates less noise and better audio quality. Generally, SNR should be at least 63 dB, with high-fidelity speakers reaching over 110 dB.

2. Input Sensitivity

This is the minimum input voltage required to achieve the rated output power. Higher sensitivity means less input signal is needed. Typically, power amplifiers have an input sensitivity of 0.775V (0 dB) to 1.5V (+6 dB).

3. Maximum Output Power (Speakers)

The maximum power a speaker can handle in short bursts without damage.

4. Rated Power (Speakers)

The continuous power a speaker can handle without distortion, measured in watts (W). Rated power is an average value, and speakers can handle peak power up to 2-3 times the rated power.

5. Constant Voltage vs. Constant Impedance Outputs

Constant Voltage (70V or 100V) Uses voltage to drive speakers, allowing longer transmission distances and multiple speakers in parallel. However, sound quality is slightly inferior compared to constant impedance systems. Power amplifiers must match the voltage rating of the speakers to avoid damage. Constant Impedance Uses current to drive speakers, providing better sound quality but limited transmission distance (up to 100 meters). Impedance matching is crucial; for example, an 8Ω amplifier should be matched with 8Ω speakers.

3. Selecting and Configuring Speakers

1. Speaker Selection

Indoor Spaces with Ceiling: Use flush-mounted ceiling speakers without a rear cover. Indoor Spaces with Only a Framework: Use ceiling speakers with rear covers or hanging ball-type speakers. Outdoor Areas: Use weatherproof column speakers or horn speakers. Parks and Gardens: Use camouflaged speakers designed for aesthetic purposes. High-End Interiors: Use elegant hanging speakers. Fire-Safe Areas: Use fire-resistant speakers with sealed designs.

2. Speaker Configuration?

Speakers should be distributed evenly across the service area to ensure a signal-to-noise ratio of at least 15 dB. Typical background noise levels and recommended speaker placement are: ? ? ? ? ? ?

High-end office corridors: 48-52 dB ? ? ? ? ? ?

Large shopping malls: 58-63 dB ? ? ? ? ? ?

Busy street areas: 70-75 dB Speakers should be placed to ensure a sound pressure level of 80-85 dB in most environments. Ceiling speakers should be spaced 5-8 meters apart, or 8-12 meters for background music only. For emergency broadcasts, ensure that no area is more than 15 meters from the nearest speaker.

4. Amplifier Sizing

Calculation Method:

For service and business PA systems: P=K1×K2×ΣPo where: ? ? ? ? ?

P = Total amplifier output power (W) ? ? ? ? ?

K1= Line loss compensation factor ? ? ? ? ?

K2 = Aging factor (1.2-1.4) ? ? ? ? ?

ΣPo = Total power requirement For fire alarm systems, use 1.5 times the total number of speakers.

2. Example Calculation:

For a background music system with 10 speakers at 20W each: P=1.26×1.2×10×20W×0.7=211W Final amplifier capacity should be 1.3 times this value: 211W×1.3=274W

5. Installation Requirements

1. Speaker Placement

Speakers should be evenly and strategically distributed to meet coverage and sound quality requirements.

2. Power Supply?

Small PA systems can use regular power outlets, while systems over 500W require a dedicated power supply. Power should be stable, with automatic voltage regulators if necessary. The power supply should be 1.5-2 times the equipment’s power consumption.

3. Cable and Conduit Installation

Use copper-core cables for signal transmission. Cables should be shielded and routed through appropriate conduits, avoiding interference from electrical lines. Ensure proper separation between power and signal lines.

4. Lightning Protection and Grounding?

PA systems require proper grounding to prevent damage from lightning and electrical interference. Use dedicated grounding for equipment and ensure all grounding measures meet safety standards.

6. Installation Quality

1. Cable and Connector Quality?

Use high-quality cables and connectors. Ensure connections are secure and correctly matched to avoid signal loss or interference.

2. Speaker Connections?

Maintain correct phase alignment between speakers. Use reliable methods for connecting wires, such as soldering or terminal blocks, and protect connections from environmental damage.

3. Grounding and Safety Checks?

Verify all grounding is correctly installed and check the safety of power connections and equipment settings. Perform thorough inspections before finalizing the installation.

4. Testing and Adjustment?

Test the entire system to ensure all components function correctly and meet design specifications. Adjust settings as needed for optimal performance.

7. Craftsmanship Requirements for Public Address Systems

1. Construction Quality Requirements

The quality of construction in a public address (PA) system project is crucial to meeting design specifications and user requirements. Therefore, it is essential to strictly follow the design plans, adhere to standards, avoid rework and delays, and maintain detailed construction logs. Key areas to focus on include:

1. Cable Selection and Installation

During the construction of a PA system, attention is often focused on equipment, but the choice of transmission cables is also vital for achieving satisfactory sound quality. High-quality broadcasting equipment (amplifiers, speakers, etc.) is necessary, but the quality of the transmission cables also affects sound quality. Parallel speaker wires have inherent capacitance between the wires, which is not suitable for long-distance transmission as it can attenuate high frequencies and cause unclear or muffled high sounds. Twisted pair cables can effectively overcome this issue and should be used for long-distance transmission. Shielded twisted pair cables prevent electromagnetic interference and enhance cable durability, making them suitable for long-distance installations. The diameter of the cables also affects performance. Thicker cables reduce transmission loss but increase cost and installation difficulty. The choice of cables should balance performance and cost, following these standards: --Use balanced connections for all signal connections between PA system devices, with soldered endpoints. --For systems with fire alarm functions, use fire-resistant or flame-retardant copper-core cables. --Cables should be routed through steel conduits or cable trays, and should not share trays with lighting or power lines. Fire alarm system cables must have fire protection measures. The bending radius of cables should be no less than 15 times the cable diameter, and power cables should be separated from signal and control cables.??Verify cable lengths before installation and match them to the design drawings, minimizing cable splices. When splicing is necessary, use specialized connectors and leave adequate cable length at both ends with?clear permanent markings.

2. Connecting Speakers and Broadcast Lines

When connecting audio equipment, it's crucial to ensure phase consistency between speakers and broadcast lines. Phase interference between speakers can cause significant variations in sound pressure levels, leading to uneven sound distribution. Therefore, adhere strictly to wiring labels and standardized connection methods. Three common connection methods in PA systems are: -Twisting Method: Stripping insulation from wires, twisting them together, and securing them with tape or clamps. This method is simple but may degrade over time. -Screw Terminal Method: Stripping insulation and inserting wires into screw terminals, then tightening the screws. This method is commonly used. -Soldering Method: Stripping insulation, twisting wires, and soldering them together, then covering with tape. This method is more reliable and suitable for high-demand or humid environments. Regardless of the method, use tinned wire to facilitate soldering and prevent rust. Use PVC or metal conduit to protect exposed wires from junction boxes to speakers.

3. System Grounding

The PA control room should have both protective and operational grounding. To minimize interference from the power system, separate protective and operational groundings should be established. Recommended practice is to install separate copper strips for weak and strong electrical systems in their respective vertical shafts. This ensures optimal operation of the weak electrical system. The overall grounding resistance should not exceed 1Ω.

2. Construction Inspection

Due to the complexity of PA systems with numerous connections and components, thorough inspection is necessary. General inspections should include: ? ? ? ? ? ?-Safety checks of equipment installation. ? ? ? ? ? ?-Verification of power line configurations. ? ? ? ? ? ?-Accuracy of connections and terminations. Special attention should be given to device settings, such as impedance matching switches on speakers. Verify that switches are set correctly to avoid damage. Check the output selection switches on signal source devices, settings on signal processing equipment, amplifier bridging switches, and power supply settings. Once these steps are confirmed, prepare for equipment debugging. Since debugging methods vary based on specific project requirements, they are not covered in detail here.

3. Quality Records

1.Certificates, technical specifications, and documentation for speakers, enclosures, transformers, controllers, outlets, amplifiers, audio processing equipment, shielded cables, etc. 2.Pre-installation, hidden inspection, self-inspection, and mutual inspection records. 3.Records of design changes and final drawings. 4.Quality inspection and evaluation records for conduit and cable installation. 5.Records of PA system installation and debugging.

8. Major Installation Requirements

1.Equipment Installation Order

PA system equipment is usually installed in cabinets. For simpler systems, a 1.0-meter cabinet might suffice. Place frequently used equipment like the main broadcast controller at the top for easy access. For more complex systems with a 2.0-meter cabinet, position frequently used equipment between 0.8 to 1.5 meters for convenience.

2. Equipment Connection Order

Connect the computer to the main broadcast controller. Audio lines typically connect directly to the input of the preamplifier or the first channel of the mixer. The mixer outputs are distributed to each amplifier, and if using pure power amplifiers, connect to the INPUT audio input. Amplifier outputs then connect to addressable terminals, zone control boxes, or zone selectors, and finally to the speakers.

3. Wiring Considerations

For extensive wiring, separate audio and power lines using different manufacturers' cables can help avoid confusion. Plan wiring in advance to avoid missing cables, which would require redoing the entire installation.

4. Power Supply

Use a dedicated power sequencer for PA systems to ensure uniform power management and consistent device startup sequences. The main power supply should include a ground line to protect equipment and prevent static-related hazards.

5. Equipment Selection

Do not rely solely on appearance; consider user reviews and market reputation. Products from reputable manufacturers with extensive testing and experience are generally more reliable.

6. Wireless Microphones

For wireless microphones, choose UHF models for better range and signal stability. Options include one-to-one, one-to-two, one-to-four, or one-to-eight configurations. For mobile use, prefer headset microphones. Lavalier microphones may have poorer sound quality and are prone to feedback.

7. Connection Cables

Use solid connections for longevity and avoid relying on adapters, which can cause loose connections over time. Properly solder connections to ensure durability and ease of maintenance.

8. Cabinet Installation

If using deep power amplifiers, ensure the cabinet dimensions (e.g., 600x600mm) are compatible with the equipment. Measure cabinet depth and spacing before installation.

Proper planning, high-quality equipment, and meticulous installation and maintenance are key to achieving optimal sound quality and reliable performance in a PA system.