Sound accompaniment in visual monitoring systems significantly increases the information content of the image. The microphone for video surveillance and the method of its connection are selected based on the goals, the configuration of the equipment and the features of the object.
Benefits of Surveillance Systems with Microphone
Sound information from an apartment or company, obtained in conjunction with the video, allows you to make the right decisions in the current situation:
- deal with the situation in the office;
- Settle conflicts with shoppers
- monitor the behavior of teachers and students during the lesson;
- make a decision based on the results of negotiations with visitors through intercoms;
- own information on the performance of duties by nannies and other employees.
Digital cameras are often equipped with a built-in microphone, which allows you to solve only part of the tasks.
The need for an external device
Microphones integrated into the camera body reproduce the sound environment in a small space in front of the device. Under conditions of noise interference, the recorded information is sometimes not decryptable.
External microphones have several advantages:
- allow you to increase the range of confident listening;
- form a directional zone;
- have high-quality characteristics of the noise reduction system, which is important for working in industrial environments or on the street.
External devices can be placed in places of the best reception, which do not always coincide with the places where the camera was installed.
Important Features
When choosing a microphone for a surveillance camera, pay attention to the technical capabilities of the devices:
- The acoustic range determines the distance at which the received signal allows you to correctly perceive the situation, to distinguish between individual words and sounds.
- Bandwidth - a frequency range in which the amplitude-frequency characteristic is homogeneous, without dips. The optimal band is considered to be from 50 Hz to 15 kHz, which is in the range of susceptibility of human hearing.
- Automatic gain control without operator intervention removes extraneous noise created by working industrial equipment, passing vehicles.
- The configuration of the reception zone allows you to receive a signal from the desired direction. There are microphones with a circular reception zone or narrowly focused.
- The presence of a built-in amplifier is important for signal transmission over long distances or, if necessary, recognition of a quiet signal.
- The need for power to work.
Devices with protection against wind noise, the case material and the degree of moisture protection are selected based on the expected operating conditions.
Sensitivity Zone
The direction of the reception area depends on the design features. Vendors usually use the terms “lapel” and “cannon”.
The first option is small in size and has a wide viewing angle. The microphone perceives the sound environment almost around itself, which must be taken into account during installation and select the appropriate video camera. Otherwise, it will not be clear where the sound came from.
Cannon types are narrowly targeted, have increased sensitivity. Characteristics allow you to receive a signal exactly from the working area. This is important, for example, when monitoring a specific workplace.
Varieties of designs
All types of miniature microphones are divided into capacitor and electrodynamic.
In the first case, the signal source is a metallized membrane, which serves as one of the capacitor plates. When exposed to sound, the membrane vibrates, due to which the induced capacitance changes with the second (fixed) plate. The receiver generates a signal.
The disadvantages of capacitor devices are:
- significant dimensions for high-quality sound;
- high price;
- inoperability in street conditions;
- the inability to connect to low-cost fixing equipment due to mismatch in power parameters.
Electret microphones are condenser type and are suitable for indoor installation.
Most common in surveillance systems electrodynamic appliances:
- have a low cost;
- suitable for use in any environmental conditions;
- operate at frequencies characteristic of human hearing.
The downside is the lack of sensitivity, which will require an additional amplifier in the circuit.
Cable for connection
Several factors affect the choice of wire for connecting the device to the DVR:
- The distance to the microphone. If it is large, a loss of quality is possible.
- The level of electrical interference - powerful electrical equipment can induce noise on long transmission lines.
- Type and composition of equipment (analog or digital).
In the practice of installing video systems, the most common are several types of products:
- Coaxial cable is designed to transmit a signal at a distance of up to 300 m. Braid from wires or foil protects from interference. At distances up to 50 m use products marked RK-75-1.5, from 50 to 100 m - RK-75-2, from 100 to 300 m - RK-75-3. Imported analogues - RG-6, RG-59, RG-11.
- The combination cable consists of a coaxial wire and two power cores hidden by a single sheath. Products are convenient to use in cases where the power supply is located at the installation site of the recorder - lay one wire. The designation KVK-2x0.35 stands for CCTV cable combined with 2 wires, cross section 0.35 mm2. The farther to the power supply, the thicker the cores are selected.
- Stranded wires contain from 2 to 20 separate conductors, each of which can be single or multi-wire. For installation sites with a quiet electromagnetic environment, cables without braid are used.
- Twisted pair transmits a signal at a distance of up to 1000 m. UTP wires are distinguished without a shielding braid. FTP with a common foil sheath for all wires. STP is an anti-interference version in which each wire is hidden under a separate screen.
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- Twisted pair
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- Combined
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- Shielded 4-core
To pair twisted-pair and analog microphones, adapters and transceivers are used that reduce the level of interference.
The procedure for connecting analog products
There are special contacts on the back of the recorder for connecting a microphone.
Work begins with laying cables or wires:
- the distance between the camera and the recorder should not exceed recommended by the manufacturer;
- from electrical wiring to parallel running wire should not be less than 15 cm;
- cables with shields are grounded;
- radius of bends do not make less than recommended;
- at a level below 150 cm from the floor, the wires are protected by an outer sheath (corrugation, box).
Based on the configuration of the equipment, you need to connect to the recorder with the appropriate connectors: RSA or tulip.
Depending on the equipment, soldering or connectors of an appropriate design are used to connect the device.
The microphone passport shows the connection diagram of the microphone to the surveillance camera.
All connections are made when the equipment is turned off from the network.
Adhere to the color scheme of the wires:
- black - a common wire connecting the minus of the camera, power supply and microphone;
- red - connects the "plus" of the power supply and the microphone;
- yellow - signal wire connected to the central terminal of the recorder.
A color scheme other than the standard one makes it difficult to identify and troubleshoot.
Features of connecting to a digital camera
Information in digital video surveillance systems is transmitted in encrypted form.
Information is converted by the electronic circuit of the camera, so the microphone is connected to the camera, and not to the recorder.
Connection points and necessary plugs are selected based on the configuration of the equipment and the product passport.
Installation height
Choosing the installation location of an external microphone, they are guided by the parameters:
- mechanical protection from the effects of pets, vandals, accidental damage when moving furniture;
- directionality of the coverage area;
- range to the place from which you want to get information.
In most cases, it is advisable to install the device at a height of 2 to 2.5 m.
Connecting an external microphone to the surveillance camera significantly improves the quality parameters of the system, improves information content. Work is done independently or entrusted to specialists. It is important to choose the right equipment, focusing on the features of the object and tasks.
