Electret condenser microphones, not just for voices - The world is full of sound

06/19/2024 Know-How

Speech or singing: These are the applications that first come to mind when most people think of the way microphones are used. But they can do much more. Electret condenser microphones in particular offer advantages in various applications.

Sensitive and waterproof microphones can be used to detect water leaks, for example. They pick up even the faintest sounds of leakage in water, making it possible to locate a leak at low sound intensities. They can also be used to be determine flow rates or to track the path of water through different rooms.

Microphones can also be used to record audio data in nature and in animal habitats, for example to obtain information for environmental protection or sustainability projects. For instance, audio collection points in a nature reserve can be used to determine its populations and migration patterns. In addition, natural sounds such as the wind in the trees or gentle rain can be electronically processed for use as a very popular relaxation and sleep aid.

In addition, high-sensitivity microphones can supplement or in some cases even replace surveillance cameras. This is because they can detect sounds that indicate a security breach. If, for example, the breaking of a window or a gunshot is detected, the authorities or security services can be alerted immediately, enabling them to respond faster.

Microphones are available in various designs and with a range of functions. The newer microelectromechanical system (MEMS) microphones in particular offer many advantages. These include a small board area with integrated analog or digital processing electronics, precisely matched components, and easy reflow processing.

Design and operation of electret condenser microphones

For the applications described here, however, the long-established electret condenser microphones (ECMs) are the obvious choice due to the wide range of options available. In contrast to MEMS microphones, they have the advantage of being available with various directivities. This makes it possible to control the direction from which sound should be considered in the application. In addition, ECMs are available in different housing shapes and with flexible connection options.

They work as follows: When sound enters the ECM, either the electret diaphragm or the backplate is electrically charged (polarized). The sound pressure waves that move the diaphragm cause a change in capacitance that corresponds to the change in distance between the diaphragm and the backplate (Fig. 1). This also changes the voltage across this capacitor array. A junction field effect transistor (JFET) in the microphone housing serves as a preamplifier. To boost the signal to a usable output, it amplifies the change in capacitance and thus the change in voltage for further processing in the amplifier (Fig. 2).

Most ECMs have a very small package design, making them easy to integrate. They have high resolution and a very wide frequency response. Modern ECMs have a thin, lightweight diaphragm. This makes them more sensitive than dynamic microphones. However, compared to dynamic microphones, the smaller and thinner diaphragm of ECMs is usually also associated with a lower acoustic overload point (AOP). As a result, when the speech signal is weaker, other noise can cause more interference.

The path to the optimal ECM for every application

ECMs deliver clean sound – provided the specifications match the target application. The most important selection criteria are the microphone’s sensitivity, polar pattern and robustness.

A microphone’s sensitivity determines how well it picks up surrounding sound. For example, if a voice is speaking directly into the microphone, it does not need a highly sensitive microphone to pick it up. The situation is different when there is ambient noise in addition to the sound being picked up (e.g. birds chirping). In this case, a sensitive microphone is needed that can pick up and record this specific sound.

Another important factor is the position of the sound being recorded in relation to the microphone components. There are three basic directional patterns.

  • Conventional unidirectional (cardioid directional) microphones pick up sound from one main direction, usually from the front. They are equipped with sound holes at the front and rear of the capsule. Inside the capsule, sound coming from the front has priority over sound coming from the rear. This partially cancels out sound coming from the rear, resulting in a unidirectional polar pattern. Unidirectional microphones are suitable for voice control in automotive applications, for example.
  • Bidirectional (noise canceling) microphones pick up sound from two directions in a circular or spherical space around the microphone. Sound holes on the front and rear of the microphone capsule capture sound from these directions, while rejecting sound from the side of the microphone. Bidirectional microphones can be used to suppress lower frequencies from a distance (e.g. wind noise) or to record two different audio sources simultaneously.
  • Omnidirectional microphones pick up sound from all directions. They therefore cover the widest range of all directional microphone types. Low frequencies are also picked up equally well from any distance and do not dominate other frequencies. An omnidirectional microphone is particularly suitable for applications where the direction of the sound source is not specified or where all sounds in an environment need to be picked up.

ECMs do not like it hot

In addition to choosing the optimal microphone for the application, careful workmanship is also critical to ensure optimal function. This is because ECMs can be damaged by heat and/or electrostatic charge. For this reason, they must be processed in an electrostatically protected environment and the specified soldering times and temperatures must be strictly adhered to.

Otherwise, there is a risk of damage to the internal JFET, the microphone diaphragm, and the internal plastic housing, all of which are very sensitive to heat. Damage here can lead to mechanical fatigue and sensitivity changes, increased audio distortion, and even total failure.

Wide selection from PUI Audio

PUI Audio offers a wide range of EMCs for a variety of applications. The most common sensitivities are available in sizes ranging from 4 mm to 10 mm in diameter and 1.2 mm to 7 mm in height. Some models feature internal 10pF and/or 33pF capacitors to reduce feedback. Connection options include a choice of solder pads (note: not SMD), pins, or variously configured cables, with or without plugs (Fig. 3).

In addition to the standard mounting options, the supplier offers ECMs with a rubber base and waterproof felt cover. These microphones are IP57-rated and waterproof. Special versions are also available for high-temperature applications. All components are quality tested to withstand the added stress of moisture and temperature without compromising audio quality.



For more information and a direct ordering option, please visit our e-commerce platform at www.rutronik24.com.

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Figure 1: Schematic diagram of an electret condenser microphone

Figure 2: Amplifier circuit of an electret condenser microphone

Figure 3: PUI Audio offers ECMs with solder pad, pin, or cable, with or without a plug.