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General purpose of microphone.
- Apr 23, 2018 -

General purpose of microphone:

1. Sensitivity (sensitivity)

It is generally defined as the efficiency of sound conversion of microphone. I'll do it in dB. In the test standard of the relevant microphone, 0dB=1V is set, so the sensitivity of the microphone is negative. For example, the sensitivity of -58db microphone is generally selected between -28 -- -66 dB, and different USES have different sensitivity requirements. For example, the sensitivity of the laptop is relatively high, which is about 27db, while the bluetooth headset is relatively low, as long as -62db is available.

It must be mentioned that the sensitivity of the microphone is not only determined by the sensitivity of the microphone itself, but also related to the resistance R in the circuit. The size of the resistor directly affects the sensitivity of the microphone. The same microphone, with different R values, is quite different. For example, when the R value is 1k and 2k, the sensitivity is nearly 7db! Therefore, the sensitivity is conditional. The manufacturer of the microphone usually requires a given test condition, usually: 2.2k, 3v.

2. Frequency response

It is generally defined as the consistency state of the sensitivity of the microphone in the audio transmission. The frequency range of the microphone is known as 20-- -20khz, which is generally considered to be consistent, and the flatter the whole frequency curve is, the better. This is not the case in practice. In the telephone, it is hoped that the frequency response curve of the microphone is the haystack type with head to tail. This minimizes the low - frequency noise and high - end noise. The microphone in the ear tag requires the removal of less than 700hz components to avoid the low frequency noise of aircraft engines. In general conference calls, the hope is to lower the frequency of 4000hz to overcome the noise.

In the case of ultrasonic transmission, the higher the high end sensitivity of the microphone is required. So the frequency of the microphone should also be used.

3. Current and impedance.

There is a field-effect triode inside the head, whose function is impedance conversion and signal amplification, so the work of the microphone must be combined with a dc voltage, which can be selected between 1.5 and 6v. The current value of the microphone is normally dependent on the current value of FET (field effect tube). It is generally between 0.15 and 0.5mA. In this case, the FET is a constant current source, and the current value is basically the same when the applied voltage and resistance change. Therefore, we can consider that the current value of the microphone is the current value of FET. The FET current value is related to its own amplification gain index, namely transconductance (the amplification factor of the transistor) and its own impedance. It is generally believed that, within a certain range, the larger the normal current value of the microphone, the lower the impedance, the higher the amplification capacity, and the higher the sensitivity of the microphone.

The impedance manufacturer of the microphone is generally calibrated to: 2.2k. In fact, the impedance of the microphone is a range value, not a point value. In practice, the impedance of the midhead is between 700 ohms-3000 ohms, and many users use the multimeter to measure the impedance, which is not correct. The multimeter is just the dc resistance of the microphone FET.

Microphones impedance values not only affect the sensitivity of microphones itself, more important is to use microphones to affect indicators, that is to say, the output impedance of microphones must use microphones and the amplifier's input impedance match, the maximum sound transmission gain can be achieved.

4. Production and overcoming of noise.

The noise of the head is divided into its own local noise and the external noise. The local noise is very small due to the small current value of the field effect tube. The main source of the noise is the poor grounding of the metal casing. Especially in high frequency devices such as mobile phones, when the contact resistance of the midhead shell and PCB is greater than 1 ohm, there will be obvious high frequency modulation interference, namely the so-called current sound and the mosquito song. See article for a way to overcome it.

5. How to use the microphone?

(this article has been published)

6. How can bluetooth headset be equipped with microphone?

Bluetooth headset is a wireless communication product launched in recent years. The general manufacturer is to purchase the bluetooth core module and then assemble the peripheral components. The chip gain of the bluetooth ear module is very high, so the sensitivity of the microphone is not high, which is basically the lower limit of the sensitivity distribution. Because of the small volume of the bluetooth headset, the sound structure is difficult to optimize. If the sensitivity of the microphone is too high, the echo can be easily generated. Recommended sensitivity: -62--66db.

7. How does the Pc use the microphone?

The personal computer's ear mug, used to use the microphone. The computer and bluetooth are the opposite, the sound card gain is very low, the soft sound card is more. So the sensitivity of the computer to the microphone is higher, at the upper limit of the distribution. Recommended sensitivity: -50db. Most laptops require a higher sensitivity to the microphone -45- 47db.