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  传声器的通用指标:
  1、 灵敏度(感度 一般定义为:传声器声电转换的效率。用dB表示。在相关传声器的测试标准中设定为 0dB=1V,所以传声器的灵敏度值均为负值。例如:-58dB 传声器的灵敏度一般在 —28----—66 dB之间选择,不同的用途就有着不同的灵敏度要求。例如:笔记本电脑的灵敏度值要求就比较高,要在—27db左右,而蓝牙耳机则比较低,只要-62db左右就可以。
  必须提及的是:传声器灵敏度的高低不仅是传声器自身的灵敏度决定的,还与电路中的电阻R有关。这个电阻的大小直接影响到传声器的灵敏度。同样一个传声器,如采用不同的R值,灵敏度就完全不同。例如:R值为1k和2k时,灵敏度可相差近7db!所以灵敏度是有条件的,传声器生产厂家一般要给定测试条件,通常为:2.2k 、3v 。
  2、 频率响应
  一般定义为:传声器在音频传输中频率各点所对应的灵敏度的一致性状态。传声器的频响范围大夺标称为20-----20khz,一般认为,这种一致性越趋一致,整个频响曲线越平越好。但在实际使用中并非如此。如:在电话机中,就希望传声器的频响曲线是斩头去尾的草垛型。这样可以最大限度的克服低频噪声和啸叫。航空耳唛中的传声器则要求削掉700hz以下的成分,以避开飞机发动机的低频噪声频率。在一般的会议传声中则希望降低4000hz以上的频率,以克服啸叫。
  而在超声传输中,则要求传声器的频响15khz以上灵敏度越高越好。所以传声器的频响也应该视用而异。
  3、 电流与阻抗
  咪头内部有一个场效应三极管,其作用是阻抗转换和信号放大,所以咪头工作必须要加一个直流电压,可在1.5--6v之间选择。咪头的电流值正常情况下取决于FET(场效管)的电流值。一般在0.15--0.5mA之间。在这里,FET是一个恒流源,当咪头的外加电压、电阻变化时电流值基本不变。因此,我们可以认为咪头的电流值就是FET的电流值。FET电流值与自身的放大增益指标即跨导(相当于晶体管的放大倍数)、自身的阻抗值有关。一般认为:在一定的范围内,咪头的正常电流值越大、阻抗也就越低、放大能力就越高、咪头的灵敏度也就越高。
  咪头的阻抗生产厂家一般标定为:2.2k,事实上,咪头的阻抗是个范围值,而不是点值。实践中咪头的阻抗在700欧姆---3000欧姆之间,不少用户用万用表测阻抗其实是不对的,万用表测得的只是咪头FET的直流电阻。
咪头的阻抗值不仅影响到咪头本身的灵敏度,更重要的是影响到使用咪头的电器的指标,就是说,咪头的输出阻抗一定要与使用咪头的电器的放大器的输入阻抗匹配,才能获得最大传声增益。
  4、 噪声的产生与克服
  咪头的噪声分自身的本地噪声,和外界的干扰噪声。由于咪头的场效应管电流值很小,本地噪声已很小。金属外壳接地不良、封装不良、是噪声的主要来源。特别在手机等高频设备中,当咪头外壳与PCB版的接触电阻大于1欧姆,就会产生明显的高频调制干扰,即所谓的电流声、蚊鸣声。克服的方法见一下文章。
  5、 手机如何配用传声器
  6、 蓝牙耳机如何配用传声器
  蓝牙耳机是近几年推出的无线通讯产品,一般的生产厂家是购入蓝牙核心模组,然后进行外围组装。蓝牙耳机模组芯片增益很高,因此,对咪头的灵敏度要求不高,基本是在灵敏度分布的下限。由于蓝牙耳机体积小,声结构很难优化,如果咪头灵敏度过高极易产生回音。推荐灵敏度:-62--66db
  7、 Pc机如何配用传声器
  个人电脑的耳唛,用到了咪头。电脑和蓝牙恰恰相反,声卡的增益很低,软声卡更甚。所以电脑用咪头的灵敏度要求比较高,在分布的上限上。推荐灵敏度:-50db左右。多数的笔记本电脑对咪头的灵敏度要求要更高一些 -45--47db。

General specifications of microphones:
1. Sensitivity (Sensitivity is generally defined as: the efficiency of microphone sound and electric conversion. It is expressed in dB. It is set to 0dB=1V in the relevant microphone test standard, so the sensitivity value of the microphone is all negative. For example: -58dB microphone Sensitivity is generally chosen between -28-----66 dB, different applications have different sensitivity requirements.For example: the sensitivity of the notebook computer requires a relatively high value, to be around -27db, while the Bluetooth headset is relatively low , as long as -62db or so can be.
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 this resistor directly affects the microphone's sensitivity. The same microphone, if different R values are used, the sensitivity is completely different. For example: When the R value is 1k and 2k, the sensitivity can be close to 7db! So the sensitivity is conditional, microphone manufacturers generally give test conditions, usually: 2.2k, 3v.
2, frequency response
It is generally defined as the consistency of the sensitivity of the microphone at each point in the audio transmission. The frequency response range of the microphone is widely known as 20–20khz. It is generally believed that this consistency is more consistent and the entire frequency response curve is flatter and better. However, this is not the case in actual use. For example, in a telephone set, it is hoped that the frequency response curve of a microphone will be a grasshopper type that goes from head to tail. This can overcome the low frequency noise and high-end whistling to the maximum extent. The microphone in the audible deafness requires cutting off components below 700hz to avoid the low frequency noise frequency of the aircraft engine. In the general conference call, we hope to reduce the frequency above 4000hz to overcome howling.
In ultrasonic transmission, the high-frequency sensitivity of the microphone above 15khz is required as high as possible. So the frequency response of the microphone should also be used differently.
3, current and impedance
There is a field-effect transistor inside the microphone head. Its role is impedance conversion and signal amplification. Therefore, a dc voltage must be added to the microphone head and can be selected between 1.5 and 6 volts. The current value of the microphone head normally depends on the current value of the FET (field effect transistor). Generally between 0.15--0.5mA. Here, FET is a constant current source, when the applied voltage and resistance of the microphone change, the current value does not change. Therefore, we can think that the current value of the microphone head is the current value of the FET. The FET current value is related to its own amplification gain index, which is the transconductance (corresponding to the amplification factor of the transistor), and its own impedance value. It is generally believed that within a certain range, the larger the normal current value of the microphone head, the lower the impedance, the higher the amplification ability, and the higher the sensitivity of the microphone head.
The impedance manufacturer of the microphone head is generally calibrated as: 2.2k. In fact, the impedance of the microphone head is a range value, not a point value. In practice, the impedance of the microphone head is between 700 ohms and 3000 ohms. It is actually wrong for many users to measure the impedance with a multimeter. The multimeter measures only the DC resistance of the microphone FET.
The impedance value of the microphone head not only affects the sensitivity of the microphone head itself, but more importantly, it affects the indicator of the electric appliance using the microphone head. That is, the output impedance of the microphone head must match the input impedance of the amplifier of the electric appliance using the microphone head. In order to get maximum sound gain.
4. The generation and overcoming of noise
The microphone noise is divided into its own local noise and external noise. Since the microphone field-effect transistor has a very small current value, the local noise is very small. Poor metal grounding and poor packaging are the main sources of noise. Especially in mobile phones and other high-frequency equipment, when the contact resistance between the microphone housing and the PCB board is greater than 1 ohm, there will be significant high-frequency modulation interference, which is the so-called current sound and mosquito sound. See the article for ways to overcome it.
5, how to use a microphone with a cell phone
6. How to Use a Bluetooth Headset with a Microphone
The Bluetooth headset is a wireless communication product launched in recent years. The general manufacturer purchases a Bluetooth core module and then performs peripheral assembly. The gain of the Bluetooth headset module chip is very high. Therefore, the sensitivity requirement for the microphone head is not high, basically the lower limit of the sensitivity distribution. Due to the small size of the Bluetooth headset, the sound structure is difficult to optimize. If the microphone head sensitivity is too high, echoes can easily occur. Recommended sensitivity: -62--66db
7, how to use microphone with Pc machine
The deafness of the personal computer used Mito. The opposite is true of computers and Bluetooth. The gain of sound cards is very low, and soft sound cards are even more. Therefore, the sensitivity of computer microphones is relatively high, which is on the upper limit of distribution. Recommended sensitivity: -50db or so. Most laptops have higher sensitivity to the mics -45--47db.
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