Electret microphones became one of the very first - they were created in 1928 and to this day remain the most important electret devices. However, if wax thermoelectrets were used in the past, nowadays technology has advanced significantly.
Let us dwell on the features of such microphones and their distinctive characteristics.
What it is?
Electret microphones are considered one of the subspecies of condenser devices. Visually, they resemble a small capacitor and meet all modern requirements for membrane devices. Usually made of a polarized film coated with a thin layer of metal. Such a coating is one of the faces of the capacitor, while the second looks like a solid dense plate: sound pressure acts on the oscillating diaphragm and thereby causes a change in the capacitance characteristics of the capacitor itself.
The device of the electronic layer provides a static coating, it is made of the highest quality materials with high acoustic and mechanical characteristics.
Like any other device, an electret microphone has its advantages and disadvantages.
The advantages of this technique include a number of factors:
- have a low cost, due to which such microphones are considered one of the most budgetary in the modern market;
- can be used as devices for conferences, as well as installed in household microphones, personal computers, video cameras, as well as in intercoms, listening devices and mobile phones;
- more modern models have found their application in the production of sound quality meters, as well as in equipment for vocals;
- consumers are available with products with XLR connectors, as well as devices with a 3.5 mm connector, as well as wired terminals.
Like many other capacitor-type installations, the electret technique is characterized by increased sensitivity and long-term stability. Such products are highly resistant to damage, shock and water.
However, there were some shortcomings. The disadvantages of the models are some of their features:
- they cannot be used for any major serious projects, since the vast majority of sound engineers consider such microphones the worst of the proposed options;
- just like typical condenser microphones, electret installations need an additional source of recharge - although in this case only 1 V. will be quite enough
Electret microphone quite often becomes an element of the overall system of visual and sound monitoring.
Due to their compact size and high water resistance, they can be installed almost anywhere. In combination with miniature cameras, they are ideally suited to monitor problematic and inaccessible places.
Device and specifications
Electret condenser devices in recent years are increasingly being installed in household microphones. They have a fairly wide range of reproducible frequencies - from 3 to 20,000 Hz. Microphones of this kind give a pronounced electrical signal, the parameters of which are 2 times greater than that of a traditional coal device.
The modern radio industry offers users electret microphones of several kinds.
MKE-82 and MKE-01 - in their dimensions they are identical to coal models.
MK-59 and their analogues - they are allowed to be installed in the most ordinary telephone without its alteration. Electret types of microphones are much cheaper than standard condenser ones, because radio amateurs prefer them. Russian manufacturers also launched the production of a wide range of electret microphones, among which the MKE-2 model was most widely used. This is a one-way device designed for use in reel tape recorders of the first category.
Separate models are suitable for installation in any electronic equipment - MKE-3, as well as MKE-332 and MKE-333.
Such microphones are usually made in a plastic case. A flange is provided for fixing on the front panel, such devices do not allow strong shaking and power shock.
Users often wonder which microphone (electret or traditional condenser) is preferable. The choice of the optimal model depends on each specific situation, taking into account the features of the future use of equipment and the financial constraints of the buyer. An electret microphone is much cheaper than a capacitive capacitive microphone, while at the same time, the second ones win much in quality.
If we talk about the principle of action, then in both microphones it is the same, that is, a voltage appears inside the charged capacitor at the slightest vibrations of one or several plates. The only difference is that in a standard condenser microphone, the necessary charging is supported by continuous polarizing voltage that is supplied to the device.
In the electret device, a layer of a special substance is provided, which is a kind of analogue of a permanent magnet. It creates a field without any external make-up - thus the voltage that is supplied to the electret microphone is not intended to charge the capacitor, but to support the power supply of the amplifier with a single transistor.
In most cases, electret models are compact low-cost installations with medium electro-sound characteristics.
While classic capacitors belong to the category of expensive professional equipment with high operating parameters and a low-pass filter. They are often even used in acoustic measurements. The sensitivity parameters of capacitor equipment are much lower than electret ones, because they certainly need an additional sound amplifier with a complex voltage supply mechanism.
If you plan to use a microphone in the professional field, for example, to record a song or the sound of musical instruments, it is better to give preference to classic capacitive products. While for amateur use with friends and relatives there will be enough electret installations instead of dynamic ones - they ideally work as a conference microphone and a computer microphone, while they can be superficial or tie.
Principle of operation
In order to understand what constitutes the device and the mechanism of the electret microphone, you first need to find out what constitutes an electret.
An electret is a special material that has the property of being in a polarized state for a long time.
The electret microphone includes several capacitors, they have a certain part of the plane made of a film with an electrode, this film is pulled onto a ring, after which it is exposed to charged particles. Electric particles penetrate into the film to a small depth - as a result, a charge is formed in the area near it, which can work for a rather long time.
The film is coated with a thin layer of metal. By the way, it is he who is used as an electrode.
At a slight distance, another electrode is placed, which is a miniature metal cylinder, with the flat part it rotates towards the film. The polyethylene membrane material creates certain sound vibrations, which are then transmitted to the electrodes - and as a result a current is generated. Its strength is negligible, since the output impedance is of increased importance. In this regard, the transmission of the acoustic signal is difficult. In order for the low current strength and increased resistance to be consistent with each other, a special cascade is mounted in the device, it has the form of a unipolar transistor and is located in a small capsule in the microphone body.
The functioning of an electret microphone is based on the ability of different types of materials to change their surface charge under the action of a sound wave, and all materials used must have a higher dielectric constant.
Since electret microphones are characterized by a rather high output impedance, they can be brought to receivers, as well as amplifiers with incoming high impedance, without any problems. To check the amplifier for performance, you just need to connect a multimeter to it, and then look at the resulting value. If, as a result of all measurements, the operating parameter of the equipment will correspond to 2-3 units, then the amplifier can be safely used with electret technology. The design of almost all models of electret microphones usually includes a preamplifier, which is called a "resistance transducer" or "impedance matching." It is connected to an imported transceiver and mini-radio tubes having an input impedance of about 1 ohm with a significant output impedance.
That is why even despite the absence of a constant need to maintain a polarizing voltage, such microphones in any case need an external source of electrical power.
In general, the switching circuit is as follows.
To maintain normal operation of the device, it is important to supply power to it with the correct polarity. For a three-input device, a minus connection with a case is typical, in this case, power is supplied through the positive input. Then through a separating capacitor, from where a parallel connection is made to the input of the power amplifier.
The two-output model is powered through a limiting resistor, also to a positive input. The output signal is also removed immediately. Further, the principle is the same - the signal goes to the isolation capacitor, and then to the power amplifier.
How to connect an electret microphone, see below.