Electret Microphone Parameters_ Electret Microphone Model and Pin Identification

The parameters of various performance indexes of electret microphone mainly include the following:

(1) Operating voltage (UDS). This refers to the minimum DC working voltage that must be applied at both ends of the electret microphone when the microphone works normally. This parameter varies according to different models. Even the same model has great discreteness. Generally, the typical values given by the manufacturer are 1.5V, 3V and 4.5V.

(2) Operating current (IDS). This refers to the static DC current of the electret microphone, which is actually the static current of the internal FET. Similar to the working voltage, the discreteness of the working current is also large, usually 0.1 1mA.

(3) Maximum operating voltage (UMDS). This refers to the maximum DC voltage that can be withstood at both ends of the drain and source of the FET inside the electret microphone. When the limit voltage is exceeded, the FET will be broken down and damaged.

(4) Sensitivity. This refers to the size of the audio signal voltage generated by the microphone under a certain external sound pressure. Its unit is usually MV / PA (MV / PA) or dB (0dB = 1000mV / PA). Generally, the sensitivity of electret microphone is mostly in the range of 0.5 10mV / PA or - 66 - 40dB. The higher the sensitivity of the microphone, the greater the amplitude of the output audio signal under the same size of sound.

(5) Frequency response. Also known as frequency characteristic, it refers to the characteristic that the sensitivity of a microphone changes with the change of sound frequency, which is often represented by a curve. Generally speaking, when the sound frequency exceeds the upper and lower limits given by the manufacturer, the sensitivity of the microphone will decrease significantly. The frequency response of electret microphones is generally flat. The range of good frequency response (i.e. balanced sensitivity) of ordinary products is 100Hz 10kHz, the microphone with good quality is 40Hz 15KHz, and the high-quality microphone can reach 20Hz 20kHz.

(6) Output impedance. This refers to the AC impedance of the microphone output at a certain frequency (1kHz). The output impedance of electret microphone is generally less than 3K Ω after impedance transformation of internal FET.

(7) Inherent noise. This refers to the noise signal voltage output by the microphone when there is no external sound. The greater the inherent noise of the microphone, the greater the noise mixed in the output signal during operation. Generally, the inherent noise of electret microphone is very small, which is microvolt level voltage.

(8) Directivity. Also known as directivity, it refers to the characteristic that the microphone sensitivity changes with the incident direction of sound wave. The directivity of microphone is divided into unidirectional, bidirectional and omnidirectional. The sensitivity of unidirectional microphone to sound waves in the front face is significantly higher than that in other directions, and can be divided into three types: cardioid, supercardioid and superdirectional according to the shape of directional characteristic curve; The sensitivity of bidirectional microphone in front and back directions is higher than that in other directions; Omnidirectional microphones have basically the same sensitivity to sound waves from all directions. Most of the commonly used machine mounted electret microphones are omnidirectional microphones.

Electret microphone model and pin identification

Because the model names of electret microphones are not uniform among manufacturers, they do their own things and have no rules to follow. If you want to know the performance and relevant parameters of a certain model of product, you can only check the manufacturer's manual or relevant parameter manual. Under amateur conditions, electret microphones of different models can be directly replaced as long as the volume and number of pins are the same and the sensitivity and other parameters are similar. The attached table lists the main parameters of some common electret microphones for reference.

The pin identification method of electret microphone is very simple. Whether it is in-line, lead or solder pin, its bottom surface is generally printed circuit board, as shown in Figure 3. For electret microphones with 2 parts of copper coated on the printed circuit board, the copper coated connected with the metal shell shall be "ground terminal", and the other copper coated shall be "power / signal output terminal" (there are "drain D output" and "source s output"). For electret microphones with three parts of copper coating on the printed circuit board, except that the copper coating connected with the metal shell is still "ground terminal", the other two parts of copper coating are "s terminal" and "d terminal" respectively. Sometimes the printed circuit board of lead-in microphone is encapsulated inside the shell and cannot be seen (such as domestic crz2-9b). At this time, it can be identified by the lead: the shield wire is the "ground terminal", and the two core wires in the middle of the shield wire are "d terminal" (red wire) and "s terminal" (blue wire). If there is only one core wire (such as domestic crz2-9), the lead must be "power / signal output terminal".