First, the construction quality requirements
The construction quality of broadcasting system engineering is directly related to the major problems of whether the project can meet the design requirements and user requirements. Therefore, it must be constructed in strict accordance with the design plan, construction according to the standard, no rework, no work, and a construction log according to the regulations. The main points should be noted in the following aspects.
1. Cable selection and laying
In the construction process of public broadcasting systems, people tend to focus on the relevant equipment packages, ignoring the choice of broadcast transmission cables. In fact, for a public broadcasting system project, in order to obtain a satisfactory acoustic effect, in addition to high-quality broadcasting equipment (power amplifiers, speakers, etc.), the quality of the broadcast transmission cable also affects to a certain extent. The quality of the sound.
Since there is a parasitic capacitance between the lines of the parallel speaker line, it is not suitable for transmitting the broadcast signal over a long distance, otherwise the high frequency part of the sound will be attenuated, which may cause unclear and boring of the high sound. Twisted pair can effectively overcome the parasitic capacitance between lines, and the long-distance transmission of broadcast signals should use twisted-pair sheathed wires.
The shielded twisted-pair sheathed transmission cable can effectively prevent the radiation influence of the broadcast cable on other cables laid in the same tube due to the shielding net function, and can further enhance the tensile resistance of the cable, and is especially suitable for long-distance laying.
In addition to the twisted pair cable, the broadcast transmission cable also has certain requirements on the wire diameter. In theory, the thicker the wire diameter, the smaller the transmission loss of the line, but the problem that comes with it is that the construction cost has gone up and the construction difficulty has increased. Weighing the pros and cons, considering the performance price ratio, the broadcast transmission cable can be selected by reference to the following criteria:
The signal connections between all the devices of the public address system are balanced and the ends are soldered. If the system has a fire accident broadcast function, a flame-retardant copper core cable or a refractory copper core wire cable should be used.
The laying method of the line shall be laid by steel pipe or wire trough. Generally, it shall not be laid with the lighting and power lines in the same line slot. The fire accident transmission line shall adopt fire protection measures. The bending radius of the cable is not less than 15 times the diameter of the cable. The power cable should be laid separately from the signal cable and control cable. The cable length should be checked on a disk-by-disk basis, and the cable should be selected according to the length of each segment on the design drawing to avoid the connection of the cable. When the cable must be connected, a special connector should be used, and a proper margin should be left at both ends of the cable to be laid, and an obvious permanent mark should be marked.
2, the connection between the speaker and the broadcast line
When connecting the playback device, pay special attention to the problem of the phase of the broadcast between the speakers and the broadcast line. Otherwise, the phase of the sound between the speakers may interfere, resulting in a large difference in sound pressure between the points. The serious consequences of high and low fluctuations, so the construction of the line must be strictly unified line marking, and a unified connection method.
Combining various sound construction requirements, combined with the actual effects in the project, in the public address system, there are mainly three types of speaker connection methods:
The twisting method is to peel off the broadcast wire and the speaker lead end, and the two strips are divided into two strands and then twisted together, wrapped with tape or stuck with a plastic sleeve clamp. This method is simple and easy to construct, but it is easy to cause problems over time.
The speaker introduction end is a connection socket. Simply peel the broadcast wire end into the crimping slot and tighten the crimping screw. This method is currently more common.
The welding method is to peel off the outer skin at the lead end, solder it after soldering, and wrap it with tape. This method is cumbersome, but has good reliability; it is suitable for use in environments with high or humid requirements.
The above three connection methods are subject to the specific situation and the requirements of Party A. In either case, tinned wires are used to facilitate soldering and to avoid moisture or rust after a long period of time. If it is required to expose the connecting wire from the junction box to the speaker end, it should be protected by PVC threaded pipe or iron snake skin.
3. Grounding of the system
The broadcast control room should be provided with protective ground and working ground. In order to reduce the impact of the power supply system on the broadcast audio system, the protective ground and working ground should be set separately. The recommended practice is to lay a copper strip in the weak and vertical shafts as the working ground of the weak current system and the protective grounding of the high-power system, so that the weak current system can work better.
Since this method is grounded at the point of access to the earth, the total grounding resistance must not exceed 1 Ω.
Second, construction inspection
Because the entire system of the broadcasting project involves more connection points and connectors, it is also possible to make mistakes for individual reasons during installation, so careful inspection is necessary. General inspections include equipment installation safety checks, proper inspection of power supply lines, and correct connection of connectors. Another important check item is to carefully check whether the status setting of each piece of equipment meets the design requirements. In particular, some speakers have an impedance matching switch. After connecting the broadcast line, be sure to confirm that the switch is correctly placed. In this position, this point must not be forgotten, otherwise it will easily cause equipment damage. These states also include whether the output selection switch of each signal source device is correct; whether the function button of the signal processing device is proper; whether the bridge switch is set when the power is placed on the bridge request; whether the power selection switch of each device is set to 220V or the like.
After the above construction steps are all confirmed, the equipment should be ready for commissioning. For the debugging of equipment, it is difficult to unify a common method because of the different conditions of each project, and it needs to be separately classified for explanation, so it will not be discussed here.
Third, the quality record
1, horn (speaker), sound box, line transformer, controller, external socket, amplifier, amplifier, audio processing equipment, shielded cable, shielded cable and other certificates, product technical specifications and technical information.
2. Pre-inspection, concealed inspection, self-inspection and mutual inspection records of the broadcasting system installation project.
3. Design change negotiation records and as-built drawings.
4. Record of quality inspection and assessment of piping and pipe threading sub-projects.
5. Broadcast system installation and debugging records.
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