To increase the range of interception of speech signals of interest in various environments, directional microphones are used.
When listening to a speech source, the ambient noise background, which is different for urban and suburban, day and night conditions, is essential.
A directional microphone has a polar pattern that provides increased sensitivity in a certain direction (tens of degrees) much higher than in other directions.
This directionality makes it possible to significantly weaken signals and interference coming from other directions and, accordingly, to isolate the signal of interest to the subscriber from the direction of the main lobe of the radiation pattern, and the narrower this lobe is, the better this can be done.
There are four main designs currently used as directional microphones:
Microphone with interference element,
Microphone with acoustic reflective mirror,
microphone array,
Supercardioid (hypercardioid) microphones,
Gradient microphones.
The main parts of every directional microphone are:
Interference element or parabolic reflector;
Acoustoelectric transducer (microphone);
Microphone amplifier combined into one structural unit.
A microphone with an interference element is made in the form of a tubular or slot type.
In the first case, the directionality is formed using a system of tubes of different lengths directed in the same direction. The outer ends of the tubes are open, the inner ends converge at a common pressure sensor. Signals received from the main direction are summed up, and signals received from other directions are subtracted (Fig. 6.11).
Directional patterns for various ratios of sound wavelength to tube length are shown in Fig. 6.12.
Rice. 6.12. Traveling wave antenna radiation patterns for waves of different lengths.
In addition, an amplifier with telephones and a tape recorder connected to it is usually made in the form of a separate unit. A directional microphone with an interference element is a structure made of a tubular phased receiving acoustic antenna loaded onto a highly sensitive microphone or array of microphones connected in series.
The interference system is assembled from a certain number of tubes with lengths from several centimeters to a meter or more (tube sizes for different sections of the audio frequency ranges are given in Table 6.7).
These tubes are collected into a bundle - long in the middle, short along the outer surface of the bundle.
On one side (where the microphone is located), the ends of the tubes form a flat section entering the pre-capsule volume (Fig. 6.11a, b).
A pressure receiver is used as an electroacoustic transducer - a microphone capsule of an electrodynamic, electromagnetic or condenser type.
The directivity pattern of the interference element is determined by the coincidence or difference in the phases of sound vibrations coming from the tubes into the pre-capsule space.
An option for placing an electoral system made up of 7 directional tubes is shown in Fig. 6.116.
The microphone is located at the focus of the parabolic catcher. Further amplification of the signal occurs through the use of a highly sensitive microphone amplifier.
This directional microphone covers the frequency range from 300 Hz to 3300 Hz, i.e. main information range of the speech signal.
If it is necessary to obtain better speech perception, then it is necessary to expand the range of received frequencies. This can be done by increasing the number of resonance tubes, for example, up to 37 pieces. In table 6.7 provides calculated data for use in a selective system from 1 to 37 tubes.
Table 6.7
| № | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| b, mm | 550 | 400 | 300 | 200 | 150 | 100 | 50 |
| R, Hz | 300 | 412 | 550 | 825 ^ | 1І00 | 1650 | 3300 |
Given in table. 6.7 resonant system covers the frequency range from 180 Hz to 8200 Hz. An option for placing resonant tubes is shown in Fig. 6.IV, where the tubes are arranged in a “snail”.
In relation to the maximum set of tubes (n = 37) for a frequency of 1000 Hz (si = 2.5 cm), the directivity index of the interference system is equal to 8 dB.
The acoustic antenna system of a slit microphone consists of a hollow tube with a system of receiving holes located on the surface of the tube (Fig.b.Iza).
Fig.6.13a. Slit microphone circuit.
A microphone is installed at one end of the tube, which converts sound signals coming from the receiving holes in the tube into a total electrical signal.
It should be noted that the overall dimensions of slot microphones are up to
Rice. 6.136. Design of the highly directional microphone "Veresk".
quite compact - for example, the length of the antenna element is in the range of 40-60 cm.
Examples of such microphones are devices such as “Heather”, “Tunnel”, “Flute”, etc. The complex of special highly directional microphones "Veresk" is designed to work with magnetic recording devices when receiving sound signals from remote sources. It consists of: a highly directional microphone, an electronic amplifier and headphones.
The device provides a nominal frequency range of 300 - 5000 Hz, with a sensitivity of 40 mV/Pa.
The equivalent sound pressure level due to its own noise is no more than 20 dB.
The gain is at least 60 dB.
The length of the beam microphone is 460 or 660 mm. The composition of the kit is shown in Fig. 6.136. Windproof covers of interference elements are essential for outdoor work.
Figure 6.14 shows a sample of a directional microphone designed for use in the field.
In (L.1) it is noted that with the help of directional slot microphones, such as “Tunnel” or “Flute”, it is possible to listen to and record speech signals on a tape recorder at a distance of 15-20 meters in urban conditions. In this case, the factor limiting the range is not the directionality of the acoustic system, but the intrinsic noise of the electret microphone head.
A directional microphone with a mirror consists of a surface reflecting the acoustic wave and a sensitive low-noise microphone located at the focus of the reflecting surface (paraboloid) (Fig.
6.15 and 6.16), an amplifier, telephones for listening and a voice recorder for recording acoustic signals.
The principle of obtaining the radiation pattern of a microphone with a parabolic mirror is shown in Fig. 6.15. The geometry of the mirror ensures that sound rays located at a certain angle 0 are focused on the microphone.
Focusing of reflected sound into the focal area where the microphone is located occurs at sound wavelengths smaller than the transverse size of the reflecting surface. To fulfill this condition, it is necessary to use mirrors with a reflecting surface diameter of 0.3 - 0.6 meters (Fig. 6.16.).
Rice. 6.16. Designs of directional microphones with a parabolic mirror.
In practice, microphones with double reflecting mirrors are also used (Fig. 6.166).
A group of pressure sensors located (usually) in the same plane is used as a microphone array.
In the simplest case, signals from sensors are summed, but there are also more complex methods of electronic signal processing.
Figure 6 L 7 shows a family of radiation patterns of a rectangular summing array for various ratios of the sound wavelength to the length of the side of the array.
As can be seen from the curves in Fig. 6.17, microphone arrays have greater directivity than directional microphones with an interference element.
The polar pattern is one of the most important characteristics of a directional microphone. It allows you to evaluate the effectiveness of using a microphone in various acoustic conditions.
In conditions of a low-frequency urban background, relatively uniformly arriving at the microphone from all sides, the directionality of the microphone makes it possible to reduce the background level by as many times as the area under the directional pattern of the microphone at a given wavelength is less than the entire area of the graph. From Fig. 6.17 it can be seen that in urban background noise conditions, the length of the traveling wave antenna and the lengths of the sides of the microphone array must be at least 0.3 - 0.5 meters.
Tests of an experimental microphone array have shown the possibility of listening and recording speech in city conditions from a distance of up to 50 meters with an array size of 450x350 mm.
Currently, designs of directional microphones have been developed with the ability to transmit intercepted information over a radio channel. An example of such a system is RMK112 "Case".
A directional microphone with an acoustic grille camouflaged in the top cover of the case provides control of acoustic information at a distance of 40 m from the object with the possibility of simultaneous recording on a voice recorder and transmission via a radio channel with quartz frequency stabilization. The maximum of the radiation pattern (Fig. 6.18.) is located perpendicular to the plane of the top cover of the case.
Fig.6.17 Directional patterns of a microphone array for waves of different lengths.
Rice. 6.18. Design (a) and polar pattern (b) of the RMK112 microphone.
Such a microphone has the following main characteristics:
Microphone polar pattern width:
in the frequency range - 35 degrees; at the central frequency (2 kHz) - 20 degrees; acoustic array gain + 10 dB;
audio frequency bandwidth 600 -4000 Hz;
microphone range - up to 40 m;
operating frequency of the transmitter for transmitting information 416.5 - 423.5 MHz; transmitter operating power 10 mW; type of modulation \\TM; transmission range 200 m: supply voltage: internal - battery. 3.6 V; external - 6 V;
continuous operation time - 20 hours; case dimensions - 100x350x420 mm.
To record information, the case is equipped with a Bolu 727 voice recorder or a TR-6 tape recorder.
The recording of the tape recorder and the power switching of the radio channel unit are controlled by hidden switches located in the lock on the front panel of the case.
By using a combination of microphones with different directivity, a combination microphone with a directional pattern can be obtained. For example, combining a pressure gradient sensor, which has a figure-of-eight radiation pattern, with a pressure sensor produces a combined sensor with a cardioid radiation pattern. The combination of a matched pair of cardioid microphones creates what is known as a supercardioid microphone. Possible characteristics of such microphones are shown in Fig. 6.19.
In practice, a combination of a cardioid microphone with an interference microphone is also used.
Fig.6.19. Polar patterns of cardioid and supercardioid microphones.
[ - cardioid microphone; II - supercardioid microphone.
This is a powerful element that allows you to create a microphone that provides interception of speech signals in city conditions at distances of 12-15 meters (for example, BEIHNE1MKN815T Germany).
Directional microphones consist of a diffuser as well as an amplifier. Many modifications are used by intelligence agencies. Modern devices are produced with and without filters. Many modifications can boast high sensitivity. According to experts, it is more advisable to purchase a model with two
The minimum threshold frequency is on average 300 MHz. Impedance sensitivity does not exceed 3 mV. Many models use two amplifiers. In this case, the conductivity of the audio signal increases quite significantly. On the market, a directional microphone for professionals costs approximately 12 thousand rubles.
To make a directional microphone with your own hands, you first need to install a diffuser. Many experts recommend using diode devices in this situation. Their minimum sensitivity is on average 4 mV. It is also worth noting that the microphone will require a small filter that will cope with impulse noise. It is more advisable to select amplifiers of the low-frequency type.
Their energy consumption is not too high. It is also worth noting that they are compact and will not take up much space in the device body. The battery itself is installed behind the diffuser. To increase signal conductivity, it is recommended to use a constant adapter.
These directional microphones receive mostly positive reviews. According to experts, the signal conductivity in the device is quite high. A high-quality amplifier deserves special attention. This microphone uses a linear type. The protection system is class PP40.
The operating humidity of this series microphone is 40%. According to experts, the diffuser is perceived without problems. Foreign objects significantly reduce the quality of hearing. This directional microphone works great at a distance of up to 130 meters. In this case there is a linear audio output. The modification costs around 8800 rubles.
This directional listening microphone is manufactured with two dipole triodes. The amplifier is standardly used of the low-frequency type. The impedance sensitivity indicator is 3.3 mV. According to experts, the conductivity of the signal at low frequencies is quite high.
The conductor for the modification is located at the rear of the device. It is also worth noting that the model is equipped with an excellent PP42 class protection system. All this suggests that the modification is capable of operating at a distance of over 130 meters. Voice audibility at high frequencies is quite high. The compact size of the microphone deserves special attention. The price for this product starts from 13 thousand rubles.
The microphone (directional) of the presented series is distinguished by high audibility quality at low frequencies. The modification's filter is used with a diode adapter. According to experts, the diffuser has low signal conductivity. It is also worth noting that the model has problems with rapid discharge. The battery in the device is lithium type and is designed for five hours of operation. His energy reserves are extremely small. The amplifier in the model is of low quality. The device costs approximately 12,300 rubles in stores.
This microphone (directional) is great for listening at a distance of over 100 meters. According to experts, low frequencies are heard perfectly. The microphone adapter is quite high quality. It is also worth noting that the diffuser is capable of operating at high humidity. A small filter that filters out unnecessary sounds deserves special attention.
It filters out interference from extraneous vibrations quite efficiently. However, there are still shortcomings in the device. The model copes poorly with high frequencies at long distances. There is no linear audio output in this case. It is also worth noting that the model discharges quickly. In this case, the battery indicator sometimes burns out. The modification costs approximately 14,300 rubles in our time.
This microphone (directional) is most suitable for working at a distance of no more than 140 meters. Its signal conductivity at low frequencies is quite high. At a distance of up to 80 meters, voice audibility is very good. The adapter for the battery in this case is of the dipole type. This microphone only uses one diffuser. A linear coaxial output is used to connect headphones. The modification also has a 3.5 mm jack. The sensitivity of high frequencies in this case is 3.3 mV.
According to experts, the device is not best suited for professionals. The model does not have a power indicator. It is also worth noting that the diffuser does not cope well with higher frequencies. There is no adapter for linear video output in the device. The manufacturer does not provide a battery charge indicator. This directional microphone for listening at a distance costs about 10-11 thousand rubles.
This microphone (directional) is manufactured with two diffusers. According to experts, the conductivity of the signal at low frequencies is quite high. Voice audibility is good at a distance of up to 100 meters. In this case, there is no filter for impulse noise. It is also worth noting that the microphone amplifier is selected without an adapter.
If we talk about connection, it is important to mention the presence of a coaxial connector. The modification also has a linear audio output. The audibility of high frequencies over a long distance is not very good. In this case, the sensitivity of the amplifier is at the level of 2.2 mV. According to experts, the microphone is not particularly good for professional use. It should also be noted that the kit does not include a case. A directional microphone for listening at a distance costs about 14 thousand rubles.
This is a compact and high-quality microphone. According to experts, the model is quite often used by intelligence agencies. The operating humidity of the device is 44%. It is prohibited to use it at temperatures above 45 degrees. The modification's diffuser is of the diode type, and the adapters for it are matched with two contactors. The model has a standard low-frequency filter. The amplifier itself is used with a low-impedance adapter.
The threshold sensitivity parameter reaches a maximum of 4.3 mV. If you believe the arguments of experts, then the model copes remarkably well with wiretapping at a distance of over 150 meters. Amplifier malfunctions are quite rare. The microphone protection system is PP40 class. The price for this model starts from 10 thousand rubles.
This is a professional and high quality microphone. According to experts, the signal conductivity at low frequencies is acceptable. It is also worth noting that the device can be used in wet weather. The linear output KE is used in this case.
The device also has a 3.5 mm jack. The microphone uses a 2 A lithium battery. If you believe the experts’ arguments, the model does not cope well with high frequencies. The modification's filters are used with copper insulators. The dimensions of the microphone are compact. The price for it starts from 9300 rubles.
This microphone is not suitable for short-range listening. The impulse noise filter is of low quality. However, it is worth noting the compactness of the modification. The adapter is attached to the microphone very securely. The sensitivity indicator is no more than 3.2 mV.
It is also worth noting that the model’s diffuser rarely breaks. The battery is used only at 3 A. The protection system is used class RK40. The operating humidity of this microphone is 34%. The user can purchase the product for 8,300 rubles.
In this article we will look at the main types and mechanism of operation of remote wiretapping devices.
Microphone technology for long-distance listening varies depending on the type. Based on the principle of operation, we can distinguish three categories of remote listening devices:
A directional microphone is used for remote listening in open areas and recording telephone conversations. The main problem with directional microphones is the distance to the sound source. Already at a distance of one hundred meters, the sound will weaken so much that it is almost impossible to separate speech from interference.
There are 4 types of directional eavesdropping mechanisms:
Professionals use a whole kaleidoscope of directional listening devices. However, most of this list is not for sale. “Mere mortals” have access to parabolic microphones, which you can buy in special online bug stores.
Using a laser listening device you can hear what's going on in the room. It reads the vibration of a window in a room. The device sends a laser beam onto the glass. Having reflected from the glass, the laser, altered by vibrations, returns to the device. The device decrypts the signal and we hear the sound.
The range of laser use is up to 0.5 kilometers. You don't have to give away your position to the wiretapping target. Without suspicious bugs, you can listen to any intimate conversation on the phone.
The cheapest laser microphone in Moscow costs about half a million rubles. You can buy cheap homemade versions, however, they will not work correctly. If they work at all.
If you and the target of wiretapping are separated only by a concrete wall, then choose this device. The microphone picks up the slightest vibrations of the wall and converts them into sound. Its operating principle is similar to that of a laser. The only exception is you will have to be at least in the next room.
In order for the device to work correctly, you need to configure the sound. To do this, lean the microphone against the wall and adjust the sensitivity. As soon as you hear understandable speech, you can use it.
The device for direct wiretapping through the wall is cheap. You can buy it in special bug and phone stores for about five thousand rubles.
We looked at the types of listening devices at a distance. You have probably already chosen for yourself what type of device to replace the notorious bugs with. In the next paragraph we will look at popular models of listening devices.
As with all parabolic devices, it uses concave parabolic plate made of plastic. This device comes with headphones and binoculars with 8x magnification. The built-in voice recorder allows you to record short conversations. You can connect headphones so that nothing interferes with listening to the target.
A microphone with a dish allows you to listen to a conversation at a distance of up to one hundred meters. With up to 70dB of audio amplification, the Super Ear 100 is extremely sensitive, and you can set it to a maximum output of 105dB to record any phone conversation.
This beauty is powered by a 9-volt “crown”, which will live 55 hours. Weighs a little over a kilogram. Thanks to its durable design, it is able to listen to the environment and phones in any frost or heat.
The price of Super Ear 100 ranges from 3,500 to 5 thousand rubles.
Like the previous copy, can pick up sounds from a hundred meters away. However, it does not have a special cymbal and is smaller in size than a stage microphone. Battery life is up to 300 hours.
The wind will not be a problem with it, since the Yukon is equipped with a modern noise reduction system. You can adjust the volume and sound strength yourself.
The microphone can be attached to binoculars, a spotting scope, or a camera. It will be convenient for you not only to listen to the target, but also to observe it. There is also a tripod mount.
This device is eagerly used reporters and cameramen in sound studios, because it won't be difficult to record professional-quality audio.
Yukon price - from 4200 to 6 thousand rubles.
We looked at listening devices that can replace bugs. A person of any income and profession can afford them. In this case, you do not need to be close to the target, and the bug will not arouse suspicion.
However, remember that illegal espionage is a criminal offense. You can end up in not-so-remote places for a long time only for installing a bug or recording a secret conversation without the consent of the target and the law. So make sure you don't break the law. Let your conscience guide your actions.
Today we continue our articles on spy technologies, namely, today we will try to assemble a directional microphone for listening to neighbors behind the wall. Sometimes a bug is less useful for wiretapping and there are places where it is simply impossible to drop a radio transmitter for various reasons. Or let’s say you really need to listen to some person’s conversation, but you don’t have access to his house... And here a microphone comes to the rescue, which is specially made for such purposes. The device itself will be mounted in a silicone gun.
The directional microphone is powered from a low-voltage power source of 3 - 6 volts. It is convenient to use lithium batteries from a mobile phone with a voltage of 3.7 volts and a capacity of about 800 mA. The operating current of the device ranges from 50 to 120 mA, depending on what type of transistors we use. The entire design of the directional microphone fits perfectly into the specified housing and is small in size. The piezoelectric head receives the signal, then the signal is amplified by a pre-amplifier assembled on transistors VT1 and VT2, later passing through a filter, low frequencies are cut off from the signal and the processed signal is sent to the final amplification stage. The degree is so high that it allows us to hear even the whispers of our neighbors. The device uses an ordinary piezoelectric head. See the directional microphone diagram below:
Almost any high-impedance speaker with a resistance of at least 25 ohms is suitable as a headphone; in this case, a small head with a resistance of 32 ohms is used. All transistors can be replaced with imported ones - this will reduce the size of the board and can positively affect the overall quality of the directional microphone. It is possible to use SMD components. Instead of the final amplifier stage, you can also use an amplifier, for example, on a microcircuit, assembled using a bridge version, but when using microchips, the sensitivity may be halved, but it is simpler. You can power the general board of the directional microphone design from two AA batteries with a voltage of 3 volts, but the use of a battery is convenient because it can be charged and reused, and in addition, the battery ensures long-term and reliable operation of the device.
A piezo microphone head is placed in a specially made umbrella in order to concentrate sound waves at a single point - this, in turn, pre-increasing the spectrum of the speech stream. The main thing is not to confuse the polarity of the head by connecting the central part of the head to the plus according to the circuit.
It is better to isolate the battery from the general body to avoid background noise, and it is also necessary that the earphone is located at a certain distance from the device, which is exactly 1 meter. If the piezoelectric head is replaced with an electret microphone, the device will turn into a directional microphone, it is capable of picking up human speech at a distance of about 15 meters. True, in this case you will not be able to hear conversations behind the wall.
If you need a powerful means of covert listening at a distance in the forest, for observing birds and nature, then a directional microphone will be an excellent solution. This is a professional device for directional sound capture, allowing you to record the chirping of birds, the sniffing of beavers, the puffing of hedgehogs and the grunting of squirrels - at a distance with noise filtering.
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Directional microphone “Super Ear SD-REC” designed for listening and recording remote sounds located in the line of sight. The parabolic antenna for sound concentration has a gain of up to 70 dB - this means that you can hear quiet sounds at a distance of up to 50-100 meters.
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The remote microphone-earphone resembles a pistol with a locator and headphones connected to it. At the opposite end of the handle there is a highly sensitive microphone capable of amplifying sound vibrations located at some distance. Depending on the model and its power, the distance to the object varies from 30 meters to 100 meters or more. Over long distances, sound is attenuated, so directional microphones have a high threshold sensitivity. But as a negative factor, acoustic noise is mixed into the data obtained, which can significantly reduce the level of the required sound. Most models of directional microphones allow you to select the necessary signal over a considerable distance by adjusting the sound frequency, while eliminating unnecessary noise.
The device is equipped with an optical zoom lens, allowing you to see what is happening in detail. The “Super Ear” microphone is thought out to the smallest detail, so the eyepiece is equipped with a soft plate that provides comfortable contact with the skin of the face. The price in Moscow for these devices depends on their capabilities and the number of functions they perform.
There are several types of directional microphones:
When choosing a remote microphone for drying birds, you need to pay attention to some parameters in order to best solve the problem at hand.
It also matters:
. under what conditions wiretapping is required;
. what is the distance from the user to the capture object;
. is there a need for recording;
. noise level at the facility.
An excellent universal option would be the Super Ear directional microphone. This is the choice of real professionals, as confirmed by expert reviews. You can buy it in any city, including Moscow.
So, the Super Ear 100 directional microphone has the following parameters:
. Amplification of sounds at a distance of up to 100 meters. At this distance, the active directional microphone picks up even quiet sounds.
. Ability to record sound onto a removable SD memory card. The Super Ear 100 microphone comes with a 2 GB mini SD card as standard. This is enough to record a large amount of audio material.
. Built-in optical system. The directional microphone Super Ear has a built-in optical monocular. With its help, you can zoom in on an object eight times for covert surveillance, in addition to wiretapping.
. Possibility of autonomous operation up to 60 hours. This parabolic microphone is powered by a Krona battery. Thus, active wiretapping is possible for more than two days, without the need to change the battery.
. On-ear headphones. They are soft and comfortable. They are comfortable to use for a long time.
. Possibility of listening to recordings. The remote microphone has functional buttons on the body. They are used to switch records.
. Affordable price. With its professional focus and powerful characteristics, the Super Ear directional parabolic microphone is easy to buy. It has a low cost in comparison with foreign professional equipment of a similar type with similar characteristics.
. Versatility of use. Remote microphone and earphone with the ability to play recordings, suitable for many purposes;
- observation of animals in the natural environment;
- assistance to people with hearing problems;
- room scanning
. Easy to use. Anyone can use a parabolic microphone, without any preparation or complex setup.
Absolutely anyone can buy a directional microphone; it will provide good audibility and visibility of a distant object.
