When designing a long-distance public address (PA) system, the connection methods and wiring planning for high-power audio equipment are often overlooked but are critical. Public address systems are commonly used in schools, large industrial parks, stations, stadiums, or outdoor large-scale events, covering wide areas, long cable runs, and numerous devices. Therefore, it is essential to thoroughly consider line loss, equipment interference, wiring methods, and effective power distribution during the design phase.
Constant voltage PA systems (commonly 70V or 100V) hold a significant advantage in long-distance public broadcasting. Compared to standard low-impedance systems, constant voltage systems operate at higher voltages and lower transmission currents, resulting in less line loss—making them ideal for long-distance transmission. During the design stage, it is necessary to plan the number and distribution of speakers in each area according to the actual site conditions, estimate the power requirements for each zone separately, and avoid centralized loads that may cause system instability or cable overload.
Power Consumption Calculation
The biggest challenge in long-distance broadcasting is power loss and external interference on the lines. Power loss directly depends on the cable specifications and length. The longer and thinner the cable, the more significant the power loss. Therefore, detailed calculations are required during design. In actual projects, copper-core speaker cables are usually used because copper has better conductivity and lower resistance. According to actual needs, the American Wire Gauge (AWG) standard is used to determine the cable thickness. For example, for distances of several hundred meters, using thicker copper wires (such as 14AWG or thicker) can effectively reduce power loss.
The specific calculation for power loss is: Line Power Loss (W) = I² × R, where I is the current in the line and R is the total resistance. The line resistance can be calculated by the formula R = ρ × L / S, where ρ is the resistivity of the conductor material, L is the cable length, and S is the cross-sectional area. With these calculations, you can accurately assess power loss and avoid sound distortion caused by insufficient power.
During cable installation, interference protection is also crucial. Cables are generally protected using dedicated cable trays or PVC conduits, which can effectively reduce the impact of environmental factors such as moisture, corrosion, and mechanical damage. When wiring, avoid proximity to high-voltage, lighting, and motor equipment lines to reduce electromagnetic interference risks. In addition, using shielded cables is a common solution to effectively resist external electromagnetic interference and ensure signal transmission quality.
When selecting power amplifiers for the actual system, it is necessary to consider a certain power margin, especially in large broadcast areas or noisy environments. Choosing equipment with slightly higher power than the calculated requirement is essential. This ensures sufficient broadcast volume and reserves space for future system expansion.
Application Scenarios
Take campus broadcasting as an example: multiple zone amplifiers are usually used to control different areas, such as teaching buildings, stadiums, and dormitories. This approach reduces the load on a single line and improves overall stability and ease of troubleshooting. In factory environments, especially in noisy workshops, in addition to reasonable zoning of amplifiers, it is necessary to increase the power and density of speakers to ensure effective sound coverage.
For temporary outdoor event broadcasting, the focus should be on quick and secure connections. It is especially important to choose cables that are flexible, wear-resistant, and have good tensile strength. Terminal connections or soldering are recommended, and insulation, moisture-proof, and anti-corrosion protection should be applied at connection points to prevent failures caused by poor contact or environmental factors.
After installation, the system must undergo thorough commissioning, including power measurement, speaker sound tests, inspection of cable connections, and confirmation of grounding. Ongoing maintenance is equally important, including regular cleaning, moisture protection, tightening of connection points, and assessment of cable aging.
In summary, the key to successful design and connection of long-distance public address systems lies in scientific and rigorous wiring planning, reasonable power distribution and equipment selection, strict interference protection, and detailed construction and maintenance plans. Only by excelling in these aspects can a public address system operate stably and reliably over the long term.