In professional performance audio systems such as stage performances and
live sound reinforcement, noise is a common and very headache problem. The noise
generated by a set of professional audio system is in different conditions. It
may come from multiple aspects. The sound engineer should analyze and judge the
more complicated conditions, and deal with them separately. According to past
experience, general noise may come from three aspects: firstly, the equipment is
not properly connected; secondly, the disturbing noise of the power supply; and
finally, the inherent noise of the equipment.
1. Eliminate the inherent noise of the equipment
The professional performance audio system is composed of multiple devices,
such as microphones, DVD decks, mixers, effects, equalizers, compressors,
encouragers, electronic crossovers, power amplifiers, speakers, etc., each
Equipment may be the source of noise. In order to find and judge from which unit
the noise is generated, it is necessary to detect the inherent noise of each
unit.
Open the professional audio system: the order of starting is opened step by
step in the order of the signal flow. After turning on, there is noise from the
speaker. First, you can turn off the power of the wireless microphone receiver
to identify whether there is noise. If the noise disappears, it proves that the
noise is generated by the wireless microphone receiver. If there is still noise,
it proves that the noise is not generated by the wireless microphone receiver,
and other units can be detected.
2. Eliminate the disturbing noise of the power supply
Noise interference of light thyristor: On the stage, the most disturbed by
power supply noise is the noise from light thyristor, because the light and
dark, intensity changes of theaters and dance halls are not achieved by changing
the voltage of 0 ~ 220V. , But through the electronic circuit to control the
conduction angle of the thyristor, change the conduction area of the sine wave
of the alternating current, and realize the change of the control power
transmission.
Therefore, the sine f sine wave in the power supply is changed to a shape
similar to a sawtooth wave, and obvious 50Hz ripples occur in the power supply,
which shows obvious noise in the professional audio system. In order to
eliminate the disturbing noise of the thyristor, the most effective method is to
provide two phases of the three-phase power supply to the light, and use the
other phase as a professional performance audio system, so as to avoid the light
thyristor. disturb.
3. Eliminate noise caused by improper connection of equipment
In the professional performance audio system, there is a common problem of
equipment interconnection. If the connection is improper, the system indicators
will decrease, noise will occur, and the equipment will not work properly in
severe cases. The following points must be done when connecting.
Impedance matching: In the professional audio system, almost all devices
use the jumper method, that is, the output impedance of the device is planned to
be small, and the input impedance is very large. This is because in the system,
unless the signal is transmitted over a long distance, it is generally treated
as a short line. Moreover, the signal level is low, and the signal is required
to be transmitted with high quality, and the change of the load basically does
not affect the quality of the signal.
When the signal source is planned as a constant voltage source, or the load
is much larger than the internal impedance of the signal source, the above
requirements can be satisfied. In fact, the impedance of professional audio
equipment is planned according to the above principles, and the jumper method is
used for the interconnection of the equipment. This is the impedance matching of
professional audio equipment.
When planning the sound reinforcement system, it is generally not necessary
to consider the impedance problem. However, when the output of one device needs
to be connected to multiple devices, that is, when a signal source drives
several loads, an active or passive audio signal distributor must be selected to
meet the requirements of the impedance matching of the device (if there are two
devices, Generally, it can be directly connected to the output terminal of the
front-end equipment).
Professional performance audio amplifiers and speakers are connected
according to the nominal output impedance and the input impedance of the
speakers. The output impedance of the power amplifier has two types, 4Ω and 8Ω,
which can be connected to 4Ω speakers or 8Ω speakers. When connected to a 4Ω
speaker, the output power of the power amplifier is greater than that of 8Ω. Two
8Ω speakers can be connected in parallel to the output end of the power
amplifier, which is a 4Ω working condition.
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