Directional microphones consist of a diffuser as well as an amplifier. Many modifications are used by special services. Modern devices are produced with and without filters. Many modifications can boast of high sensitivity. If you believe the experts, then it is more expedient to purchase a model with two
The minimum threshold frequency averages 300 MHz. The impedance sensitivity does not exceed 3 mV. Many models use two amplifiers. The conductivity of the sound signal in this case increases quite strongly. On the market, a directional microphone for professionals costs about 12 thousand rubles.
How to do it yourself?
To make a directional microphone with your own hands, you first need to install the diffuser. Many experts in this situation recommend the use of diode devices. Their minimum sensitivity index 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 expedient to select amplifiers of a low-frequency type.
Their energy consumption is not too high. It is also worth noting that they are compact and do not take up much space in the device. The battery is directly installed behind the diffuser. To increase the conductivity of the signal, it is recommended to use a constant adapter.
Parameters of King EH031 Devices
These directional microphones reviews are mostly positive. According to experts, the signal conductivity in the device is quite high. A quality amplifier deserves special attention. This microphone uses a linear type. The protection system is used class PP40.
The working humidity of the microphone of this series is at the level of 40%. If you believe the experts, then the diffuser is perceived without problems. Foreign objects significantly reduce the quality of hearing. This directional microphone works great up to 130 meters away. Linear audio output in this case is available. There is a modification in the region of 8800 rubles.
King EH035 Series Microphones
This directional listening microphone is made with two dipole triodes. The amplifier is normally used low-frequency type. The sensitivity index at the impedance is 3.3 mV. If you believe the experts, then the conductivity of the signal at low frequencies pretty high.
The conductor of the modification is located at the back 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 able to work at a distance of over 130 meters. Voice audibility at high frequencies is quite high. The compact dimensions of the microphone deserve special attention. The price for this product starts from 13 thousand rubles.
Features modifications King EH040
The microphone (directional) of the presented series is distinguished by high quality of audibility at low frequencies. The modification filter is used with a diode adapter. According to experts, the diffuser has a low signal conductivity. It is also worth noting that the model has problems with fast discharge. The battery in the device uses a lithium type, and it is designed for five hours of operation. He has very little energy. The amplifier in the model is of poor quality. The device costs about 12,300 rubles in stores.
Shure SV200 Device Options
This microphone (directional) is great for listening at a distance of over 100 meters. If you believe the experts, then the low frequencies are heard wonderfully. The microphone adapter is of good quality. It is also worth noting that the diffuser is able to work at high humidity. Special attention deserves a small filter that eliminates unnecessary sounds.
Interference from extraneous vibrations, it filters quite well. However, there are still some shortcomings in the device. With high frequencies over a long distance, the model copes poorly. There is no line audio output in this case. It is also worth noting that the model is quickly discharged. In this case, the battery indicator sometimes burns out. There is a modification in our time of about 14,300 rubles.
Shure SV300 Series Microphones
This microphone (directional) is best suited for operation at a distance of no more than 140 meters. The conductivity of the signal 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 selected dipole type. This microphone has only one diffuser. To connect headphones, a linear coaxial output is used. Also, the modification has a 3.5 mm jack. The sensitivity of high frequencies in this case is 3.3 mV.
If you believe the experts, then the device is not suitable for professionals in the best way. The model does not have an on indicator. It is also worth noting that the diffuser does not cope well with high frequencies. There is no adapter for a linear video output in the device. The battery charge indicator is not provided by the manufacturer. This directional microphone costs for wiretapping at a distance of 10-11 thousand rubles.
Features of Rode NTG-2 modifications
This microphone (directional) is produced with two cones. According to experts, the signal conductivity at low frequencies is quite high. At a distance of up to 100 meters, voice audibility is good. There is no filter for impulse noise in this case. It is also worth noting that the microphone amplifier was selected without an adapter.
If we talk about the 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 at a great 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 very good for professional use. It should also be noted that the set does not include a case. There is a directional microphone for wiretapping at a distance of about 14 thousand rubles.
Parameters of Samson R23S devices
This is a compact and high quality microphone. According to experts, the model is quite often used by special services. The operating humidity of the device is 44%. At temperatures above 45 degrees, it is prohibited to use it. The diffuser of the modification is of the diode type, and the adapters for it are selected with two contactors. The filter of the model is standardly installed of a low-frequency type. 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 with wiretapping at a distance of more than 150 meters. Failures in the operation of the amplifier are quite rare. The protection system at the microphone is applied class PP40. The price for this model starts from 10 thousand rubles.
Samson R25S Series Microphones
This is a professional and high quality microphone. If you believe the experts, then the signal conductivity at low frequencies is acceptable. It is also worth noting that the device is allowed to be used in wet weather. The KE line output is used in this case.
The device also has a 3.5 mm jack. The battery at the microphone is of a 2 A lithium type. If you believe the arguments of experts, then the model does not cope well with high frequencies. Modification filters are used with copper insulators. The microphone is compact in size. The price for it starts from 9300 rubles.
Features of the Sennheiser XSW 12 model
This microphone is not suitable for listening at short distances. The impulse noise filter is of poor quality. However, it is worth noting the compactness of the modification. The microphone adapter is very secure. The sensitivity index is no more than 3.2 mV.
It is also worth noting that the diffuser rarely breaks in the model. The battery is used only for 3 A. The protection system is applied class PK40. The operating humidity of this microphone is 34%. The user can purchase goods for 8300 rubles.
In the review, a super popular sound amplifying device called the Arbiter. This is a directional listening microphone that picks up and amplifies faint sounds up to 100 meters away. With this device, you can listen to and record various sounds, such as birdsong. Of course, you can also hear other people's conversations that the author of this video collection strongly does not recommend, because it is not good to do this.
Purchased from this Chinese store. Let's unpack and assemble the gadget. The first thing in the box is a parabolic catcher in the form of a pistol. It is equipped with an 8x magnification monocular with a buzzer to follow the object. Power button, volume control, recording, headphone connection. Headphones included.
Assembling and debugging a microphone for wiretapping
Let's start assembling and setting up the Arbiter for working at a distance. It is powered by one Krona battery, but this is not very good, since they have a small capacity. It is better to buy another battery. We install the battery. Now we fix the parabolic sound reflector.
How does a remote sound pickup work?
Acoustic vibrations from the microphone are transmitted to an amplifying device, which transmits the amplified sound to the headphones. We connect them. The audio amplifier is ready to go.
Let's check it out at work. We put on the headphones, turn on the button, point to the source. You can hear the singing of birds in the distance, the sound is really amplified by 15-20 times, you can clearly hear it. It is so loud that when a nearby bird sings, you have to turn down the power.
A great gadget for distinguishing and listening at a distance. If you use more powerful headphones, this eavesdropping microphone works better. You need closed-type headphones, the sensitivity and sound quality immediately increase.
) about DIY for shooting video using a digital camera, I paid a little attention to recording sound, mentioning the possibility of using the Sanyo HM-250 plug-in lavalier microphone and synchronous recording on an audio recorder (Alesis PalmTrack).
An external recorder (left) on the camera for synchronous sound recording, and a homemade lavalier microphone mount (right) for sound recording by the camera. The disadvantages of the first design are a rigid mount that transmits sounds from the camera to the recorder (the operation of mechanisms and hand touches). Cons of the second - a long lavalier microphone cable "catches" electromagnetic interference.
In this article, the topic of homemade products for recording sound will be continued. But first, why do something yourself. The first and main answer is because it is interesting. The second - because "the hucksters got it." Recently, in a “live store” (or rather, in a shopping mall, where, as a rule, they don’t put price tags), they offered me a mediocre Audio-Technica ATR-6550 microphone at about three times the price of what they ask in Russian online stores (reasonable, but , of course, slightly higher than in the countries of "developed capitalism"). Luckily, there's the internet for pricing, and there's YouTube, which lets you check out the sound quality without buying a microphone.
So, if you type in the search on YouTube the name of a microphone with an acceptable price (I rate it as a small addition about that simple homemade product (a lavalier microphone in a "anti-wind" holder), which was described in a previous article. I wrote that the Sanyo HM- 250 has a more or less uniform directivity (which was checked by the recording level indicators of the camera / recorder when the microphone was rotated around its axis). And also that it hears high frequencies worse than the built-in microphone of the camera. However (with a more careful and methodical analysis using a white noise generator and a program) it turned out that this microphone noticeably decreases its sensitivity to high frequencies with a lateral signal direction.Therefore, the microphone was removed from the lavalier of the holder bed (see illustrations for the previous article) and placed in the windproof holder head first (rather than sideways, as is possible with a holder bed.) The sound recorded with this design is better. the gadfly of the lavalier microphone often catch pickups, and then unpleasant hums with beats are heard in the recording. The way out is to cut (shorten) the wires and / or change them to shielded ones. Since I did not want to spoil the lavalier microphone, I decided to make a microphone from commercially available microphone capsules. Although the range of such devices in electronic stores is usually wide, not everything and not the best is available. I managed to purchase electret microphones HMO 0603B with a supply voltage of 3 V, a relatively wide range of recorded frequencies, good sensitivity and no pronounced directivity.
Homemade successful
Since it was obvious that a knowingly good capsule (or capsules for a stereo microphone) could not be found immediately, it was decided to make the design of the microphone collapsible and modular. Thus, reliability is somewhat degraded, which is very important for the final solution, but this is quite acceptable for an experimental homemade product. In the following, a normal working option will be described, as well as possible troubles when choosing other options.
Blanks for making a microphone - microphone capsules and RCA connector
Complete microphone module. A section of the connector body serves as a protective element. To stabilize the position of the primer inside the tube body, the free space can be filled with porous paper or corrugated paper rolled into a tube.
RCA connector is used for modular microphone connection. The microphone capsule is mounted on RCA pins. On the wire leading to the camera, it is wise to use a reciprocal (that is, the one for connecting a microphone) RCA connector of the "jack" type, which avoids (more likely) accidental short circuits of the camera circuit.
As a microphone housing, you can use shells from an inexpensive dynamic microphone. From such a shell, you need to remove the primer, switch, wires and ballast weight.
Cable for connecting a microphone to a camera (stereo, soldered into two mono inputs) and seals (foam rubber) for mounting it into the microphone housing
Cable assembly, ready to be installed in the microphone housing
Microphone assembly
As a mount on the camera, the design described in the last article is used. A layer of foam rubber is wound between the microphone body and the holder tube, which isolates the microphone from mechanical noise coming from the camera. To balance the microphone body, weights should be glued into its rear part.
The weak point of digital cameras when used as video cameras is the audio recording path. At least, the Canon EOS 600D I use in sound recording noticeably loses to the 100-dollar Alesis PalmTrack recorder. Even with a more or less good microphone installed, the recording quality may be low due to the mediocre amplifier and recorder built into the camera. You can reduce the effect of the internal noise of the camera's built-in amplifier by simply turning off the audio gain (for some cameras this can be done using Magic Lantern) or reducing it to a minimum while amplifying the actual signal from the microphone. To amplify the signal, I assembled a homemade "" and tested it with a camera. It turned out that such an amplifier really helps to reduce noise, but it itself catches external interference well. I was not able to install it on the camera and work normally with it - sometimes it hums, makes noise, etc. Until the problem of shielding this amplifier is solved, I tried to find a replacement for it. The requirements for compactness and low cost are met by the Fiio series headphone amplifier, for example Fiio E5. I found it on the same YouTube as an option for amplifying the microphone signal when recording a video.
Amplifier Fiio E5. On the case there are buttons for power, volume control and a bass boost switch
Amplifier is charging from USB
The Fiio E5 amplifier is not designed to work with a microphone and a camera (assuming that the load of the amplifier is low-impedance; at 16 ohms the output power will be 150 mW, at 300 ohms - 16 mW; and the input impedance of the camera, judging by the Magic Lantern website, is 2 kΩ ), and at its input there is no phantom power for amplifiers built into electret microphone capsules. For this reason, it is necessary to provide additional power for the microphone.
Standard wiring diagram for an electret microphone with two leads. The load and power resistance ratings correspond to the HMO 0603B capsule used in my design.
Modified power cord design. A 3-volt CR2032 battery and a 2 kΩ resistor are included in the circuit for each channel. When the batteries are removed, the cable works like a normal cord "without power"
When using microphones with a higher supply voltage and if you want to maintain a compact design, you can use an alternative power scheme in which both microphones are powered by one pair of batteries (6V).
To reduce the mutual influence of the channels (and with such a connection they turn out to be connected through the power circuit), resistances of 10 kOhm are installed in the load circuit. In order to balance the signals in the left and right channels, both resistances must be the same value with a reasonable degree of accuracy.
Microphone with amplifier assembly
As practice has shown, with the HMO 0603B microphone used and the above connection and power scheme, the amplifier adds a little to the signal level (on the camera amplifier, for example, you can set the gain not to 50%, but to 40% - to get a level of −12 dB, which is fundamentally not affects the noise). Nevertheless, the effect is there, and perhaps it will be better with other microphones (according to the guys who posted their video reports on YouTube).
Unsuccessful Options
The designs described above were not the first microphones I assembled. Since the on-camera microphone is relatively small, you have to use small components, including connectors. Therefore, for the first designs, I chose a 3.5 mm TRS connector (minijack). It is compact, has three contacts (in the "stereo" version) and is universal (many adapters and connectors are available). The stereo version of the connector allows you to mount both two- and three-pin microphone capsules on it and separate the signal and power circuits.
Design for testing microphones. The microphones are mounted in TRS connectors, the "ground" is connected to S (sleeve), the "plus-signal" - to R (ring) and T (tip). Stereo double converted into channel splitter
First, a stereo twin was modified to test the microphones (soldered to the TRS connector). If you open it and isolate the corresponding contacts with the help of a cambric, you will get a “stereo to 2 mono” splitter. Successful experiments with such a test design gave reason to hope that if you add wires and a power source to it, then the microphone will work too.
The insides of the microphone: a cord with two-channel wiring and built-in load resistances (I used 10 kOhm), a power supply (6 V) in the flashlight-keychain case, microphones on TRS plugs and a “safety” screw
A common problem with the TRS connector is that the “T” contact breaks off. A screw will help to remove the chip - it must be carefully screwed into the hole of the “T” contact fragment to remove this part from the inside of the socket.
Why designs with a TRS connector had to be abandoned is clear from the photo. I broke off the tip of the TRS from the microphone and the tip of the TRS connecting cord. Both times it didn't happen in the camera (meaning I was very lucky) and I decided not to risk using this type of connector again. In fairness, I note that the reason is not in the TRS connector itself, but in the quality of the components that are produced and sold. I had to deal not only with breaking contacts, but also with internal short circuits in the connectors. TRS also has one more unpleasant feature: when connecting the connectors, the contacts slide over each other and can complete the circuit in a completely different way than planned. Therefore, it is necessary (recommended) to mount all connections before turning on the power to the equipment. Assembled microphone circuits with TRS connectors, if they work, are very likely to generate noise and crackle due to poor contacts. In general, in order not to suffer with the choice of TRS connectors, I ended up choosing the more bulky and simple RCA ones ("professional microphones" are usually connected using XLR connectors - even more bulky and less versatile). Advantages of RCA: easier installation due to their large size and good separation of contacts, eliminating incorrect connection at the time of connection.
I will not argue that a homemade microphone has significantly improved the quality of the recorded sound. But subjectively, the sound of a pair of microphones is perceived as fuller when compared with the sound recorded by the microphone built into the camera. More importantly, the external microphone is more or less well isolated from the camera, and you can not be afraid to use the mechanically noisy optics stabilizer and camera focus drive, and also not worry about the ability to record camera control sounds and changes in grip. The microphone capsules used in the homemade product are comparable in sensitivity to those installed in the camera, they hear mid and high frequencies better, but, perhaps, for the same reason, they make noticeably more noise. All this can be determined by ear. I plan to devote a continuation of the article to the “objective” assessment of the quality of the microphone.
Once upon a time, I made a highly directional, highly sensitive microphone and posted the results of its tests on the Internet. Many years have passed since then, but I still receive requests to purchase this product. In the absolute majority of cases, those who wish to purchase have an idea about this product from feature films, usually detective films. Therefore, as soon as I sent them a photo, their interest in it disappeared. For those who are really interested in such a device, I decided to write this article, in which I will briefly talk about how to make it with my own hands.
Structurally, the product consists of a parabolic reflector, a receiving device located in its focus, a low-frequency amplifier, headphones and an independent power supply. The entire device is mounted on a suspension that allows you to smoothly rotate it in a horizontal and vertical plane.
To represent the purpose of each block of the device, let me remind you a little theory.
Let a stream of sound waves fall on a parabolic reflector. If the sound source is far enough away, then the sound stream can be represented as a stream of parallel vectors. Falling on the surface of the vector are reflected in the focus area (see Fig. 2). According to the wave theory, the diameter of this zone d cannot be less than the wavelength of the sound incident on the reflector. That is, d ≥ λ, where λ = c/f. Here c is the speed of sound, f is its frequency. We assume that the shape of the parabolic reflector is ideal, and therefore d = λ. From here follows the first most important characteristic of the device, its parabolic reflector gain: Kp = (D/d)2
The meaning of this ratio is very simple. The sound flux is incident on the surface of the paraboloid S = πD2/4. The paraboloid concentrates the energy of the stream at the focus on the surface of the receiving device with area s = πd2/4. As a result, the energy density of the sound flux on this surface increases by a factor of Kp = S/s = (D/d)2. In the photo, the diameter of the parabolic reflector is D = 90 cm. For a wave λ = 15 cm (f = 2000 Hz), we get Kp = (90/15)2 = 36.
Rice. 2
The second most important characteristic of the device is its sharpness of direction. This parameter is important because it is necessary not only to amplify the audio signal, but to amplify the useful signal. To do this, it is necessary to “cut” it from the general sound stream using the radiation pattern. The magnitude of the radiation pattern of a parabolic reflector can be calculated as follows. By turning the paraboloid (see Fig. 3) it is possible to turn it through such an angle α that the area of sound flux concentration will go beyond the receiving device. Since the dimensions of the receiving device are limited by the wavelength of the received sound λ, the angle of the radiation pattern in the first approximation can be expressed as follows:
α = arctg(λ/F).
In the device shown in the photo, the parabolic reflector has a focal length F = 36 cm. Hence, for λ = 15 cm, the directivity of the device will be 22 degrees. This is a fairly small angle. For this reason, a parabolic reflector with a receiving device is mounted on a suspension (see photo Fig. 1) which allows it to be rotated smoothly. Without this suspension, it is extremely difficult to work with the device. It should be added to this that the ratios of both the gain (1) and directivity (2) include the wavelength λ. As it decreases, both the gain and the directivity increase. This is clearly visible when listening to the acoustic horizon. High-frequency sounds are best heard: in nature, the cries of birds, in a residential area, the clinking of dishes from open windows and vents.
Rice. 3
As for the receiving device, which is at the focus of the paraboloid (see Fig. 4). The main part of the device is the bracket. There is a hole in its central part. On the one hand, a condenser microphone is fixed in it, and on the other, a foam piston, which is glued to the membrane, enters with a small gap. The membrane itself is glued into the bracket. The bracket has windows that connect the volume limited by the membrane with the volume of the body. To increase the acoustic volume of the body, it is filled with padding polyester or other fibrous material.
The device is placed at the focus of a parabolic reflector and operates as follows. The stream of sound waves reflected by the parabolic reflector falls on the membrane and causes it to vibrate. It follows from the theory of membranes that under the action of pressure (sound wave) the membrane bends in the form of a paraboloid of the fourth degree. That is, under the action of sound waves, it is predominantly the central region of the membrane that moves. And this means that the membrane concentrates the energy of the incident sound wave into oscillations of its central zone. As a result, the piston, which is glued into the central part of the membrane, will excite oscillations in the volume between it and the microphone with an amplitude significantly exceeding the amplitude of the sound wave incident on the membrane. The membrane gain can be estimated as follows:
Km = (Dm/dk)2
The value of dk, i.e. the size of the zone of concentration of deformations of the membrane in the first approximation, it can be taken equal to dk ≈ 0.2 Dm. Hence, the membrane gain (for Dm = 15 cm) will be: Km ≈ 25. Then the total acoustic gain of the device will be: K = Kp Km = 36 x 25 = 900.
Some practical advice for the manufacture of a highly directional high-sensitivity microphone.
Rice. 4
1. Parabolic reflector
In my device, as a reflector, I used a direct focus satellite dish reflector with the following parameters: D = 900 mm, F = 360 mm, F / D = 0.4. Reflector material - aluminum sheet 1 mm thick. Suspension (a device for turning the reflector in two planes) is standard from a satellite dish. Homemade tripod stand.
Now there are no direct-focus satellite "dishes", especially aluminum ones. They were replaced by steel offset ones. In principle, this is not so significant. The only inconvenience is that the steel plate is much heavier than the aluminum one, and because of the offset shape, the vector of its radiation pattern is not as clear as that of the direct focus. A satellite dish can be bought both in specialized companies and on the radio market. Vesta with a “plate” should also be bought with its suspension, including the converter suspension. That is, you should buy a satellite dish, but without electronics (converter and tuner). It makes no sense to use a "plate" with a diameter of less than 900 mm for the manufacture of a microphone.
2. Receiving device
Any cylindrical container of a suitable (D ≈ 150 mm) size can be used as the body of the receiving device. For example, you can use a stainless steel mug. There are a lot of these for sale now.
Inside the case is a microphone bass amplifier. I'm not an electronics engineer, so I used ready scheme amplifier and a set of KIT parts that implements it. As a microphone, I used a condenser microphone with a diameter of about 1 cm. The issues of matching the characteristics of the microphone and the low-frequency amplifier were clarified by the sellers of the KIT sets.
The output of the amplifier and the power supply to it are brought out to a five-pin connector embedded in the housing of the receiving device (see photo).
The bracket (see Fig. 3) is machined from plastic (I machined it from textolite). I do not give its specific dimensions. It is enough to ask for its outer diameter (I have 150 mm) and the diameter of the microphone (about 10 mm). The rest of the dimensions are quite arbitrary. Their ratio can be taken, for example, from Figure 4.
I drilled out the bracket windows (3 sector windows), processed the edges with a file. Then I picked up a thin-walled metal tube with a length of 50 ... 100 millimeters, with an outer diameter equal to the diameter of the microphone. After I drilled a hole in the bracket with diameters equal to the outer diameter of this tube. I sharpened the edge of the tube so that I got a notch out of it. Then he prepared a foam plate with a thickness of 5 ... 7 mm. By rotating the notch, I cut out a piston from the foam plate with it. The piston was left in the tube.
After these preparatory work, the membrane can be glued. From cigarette or other thin paper, cut out a circle equal to the diameter of the bracket. We glue it into the bracket using waterproof glue (rubber glue, glue 88, "Moment" (rubber), etc.) After the glue has dried, wet (for example with a cotton swab) the glued membrane with water and let it dry. After drying, the membrane will stretch taut. After that, a foam piston can be glued into the membrane, which is located in a metal tube. To do this, we lubricate the end of the piston protruding from the tube with waterproof glue. But not the "Moment", it intensively dissolves the foam. Rubber or 88 - oh. Put the bracket on flat surface membrane down and insert a tube with a piston into the central hole. Without removing the tube, we push the piston out of it until it comes into contact with the membrane. Then, pressing the piston against the membrane, carefully remove the tube from the bracket hole. All pistons are glued on. The question is why all these difficulties. In order for the piston to be installed in the bracket hole with a minimum clearance and strictly coaxial.
After gluing the piston on the other side of the hole, we fix the microphone. For example, we wrap paper on its side surface and firmly insert the microphone into the hole. It is desirable to make the connection of the microphone with the LF amplifier board detachable. When checking and adjusting the bass amplifier, the microphone will have to be disconnected and connected to the amplifier board many times. The bracket with a glued membrane and a microphone is fixed in the body of the receiving device with the help of side screws (self-tapping screws). After the low-frequency amplifier is configured, its board is fixed in the housing of the receiving device, for example, using hot glue. After that, the housing of the receiving device is filled with fibrous material (synthetic winterizer, cotton wool, etc. fibrous material) and closed with an assembled bracket. To protect the paper membrane from damage, it should be closed with a not very thick (8 ... 10 mm) foam rubber (polyurethane foam) plate. Close the foam rubber with a thin polyethylene film. Such protection, no matter how significantly the reception quality does not reduce, but protects the membrane from rain and wind noise.
3. Power supply
Now there are a lot of inexpensive small-sized batteries on the basis of which you can make a device power supply. In addition to its direct purpose, it is also used for switching. That is, the battery is placed in the housing, which is used to secure the following elements in it. Power switch, signal level control resistor from the low-frequency amplifier, a five-pin connector for connecting the receiving device (the cable connecting the connector of the receiving device and the power supply is visible in the photo). In addition, a headphone jack, and, if necessary, a recording device that contains an analog input.
After all the blocks are ready, the device is assembled as a whole. The receiving device is fixed instead of the converter in the focus of the satellite dish. With the help of a standard suspension, the plate is installed in a suitable tripod. We connect the power supply and the receiving device with a cable. We connect the headphones. Everything, the highly sensitive highly directed microphone is ready to work. It remains only to turn on the power and start listening to the acoustic horizon.
A directional microphone can be used both to record the voices of animals, birds, the sound of the sea, etc., and as an “electronic intelligence tool” in military sports games. In the first case, a portable tape recorder is needed, in the second, headphones are enough, for example, from a player. The directivity of the microphone significantly increases the signal-to-noise ratio at the input of the amplifier and allows high-quality amplification and recording of sounds from distant sources.
The design of the microphone, described in, is shown in fig. 4.7. The basis of the design is a cylindrical case 1 with a diameter of 60 ... 65 mm and a length of 450 ... 600 mm, which can be easily glued from drawing paper. To reduce the reflection of sound from the walls, the case is pasted over from the inside with a layer of foam rubber 2. The microphone capsule 3 is attached to the case with wire rings and rubber bands 5. They are attached near the microphone
Rice. 4.7. Directional microphone design
amplifier 6, enclosed in a screen, for example, made of tinplate from a can of condensed milk. There is a battery 10 under the amplifier. The back side of the case is closed with a cover 7, on which connector 9 and a variable resistor S (R10) are fixed.
For ease of use, a handle is attached to the case - a bracket 11 W.3 of polystyrene 5 mm thick. A nut 12 is attached to the bracket-handle, with the help of which the directional microphone is mounted on a photo tripod.
The directional microphone allows you to record sounds from up to 100 m away. Even better results can be achieved if you change the design of the directional microphone. To do this, the microphone is placed in the center of a parabolic reflector or additionally equipped with a set of resonant tubes, see, for example,. In any design, an additional increase in the range of the microphone allows narrowing the bandwidth of the amplifier. On fig. 4.8 shows a schematic diagram of an amplifier operating in the "telephone" frequency band of 280 ... 3400 Hz. It is assembled on two op-amps that are part of a fairly low-noise operational amplifier K157UD2. The cascades are identical and are non-inverting amplifiers connected in series. The lower limit of the passband of each of the stages of the amplifier is determined by the elements R1, C1 and R2, R3, C2, and the upper - by R4, C3 and R5, C4. Capacitors C5, C6 are used for frequency correction of the op amp, divider R6, R7
Rice. 4.8. Narrowband microphone amplifier
forms an artificial midpoint. Capacitors C7, C8 shunt the power circuits of the op-amp DA1. The variable resistor R2 is a level controller, with the help of its voltage gain, the voltage gain of the circuit can be changed within 50 ... 64 dB.
Headphones with a DC resistance of 16 ... 100 Ohms can be connected to the output of the amplifier (pin 9 of the DA1 chip). With a supply voltage of 6 ... 9 V, the amplifier operates stably and the power released in the load is quite enough for listening. If another type of op-amp is used, a current-limiting resistor with a resistance of 33 ... 47 Ohm may be required between its output and the connection point of elements R5, C4, pins 3 and 5 of connector X2.
The printed circuit board and the placement of elements on it are shown in fig. 4.9. Capacitors C1-C4 can be types K10-17, K10-47, K73-5, K73-9, K73-17, C5, C6 - KT1, KD. As an op-amp DA1, you can use KR1434UD1, which is an analogue of K157UD2, as well as K140UD20. In the latter case, rice
Rice. 4.9. Circuit board and placement of elements of a narrow-band microphone amplifier
The PCB will have to be corrected, not forgetting the current-limiting resistor at the output of the second op-amp (pin 10 of the K140UD20 chip). Resistor R2 type SP4-1. The types of the remaining elements are the same as in the previous scheme.
This circuit also practically does not require adjustment, you just need to make sure that there is zero voltage at the output of the circuit (between pins 2 and 3, 5 of connector XI).
