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Basic circuit knowledge in headphones

First of all to introduce some commonly used terminology that describes the nature of the headset:

1) Operating point: If the circuit to be analyzed is divided into two two-terminal networks A and B, respectively, in the same coordinate system were drawn two networks of the volt-ampere characteristic curve, the intersection of two curves called the operating point. The operating point corresponds to the current and voltage values, both A's output current and output voltage, but also B's input current and input voltage.

2) impedance matching: calculate the actual power output power can be seen when i = Io beats by dre sale / 2, the power output power of the largest. At this point the corresponding load resistance when the load resistance and power supply resistance are equal, the power output power is the largest, this is the impedance matching. In the actual circuit, the pursuit of impedance matching time is not much, because the impedance matching although the output power of the largest, but half of the power are consumed in the resistance on the efficiency is too low. In order to improve the efficiency of energy use, but also to avoid the back-end load on the front of a relatively large impact on the back of the input beats by dre impedance is generally higher than the output impedance of the front several orders of magnitude.

3) source: from the circuit point of view, the source is an active two-terminal network. If the audio signal frequency is assumed to be fixed, the source is a linear active two-terminal network that can be described by the voltage source equivalent model. In order to minimize the output signal of the audio source is not affected by the back-end load, the output impedance of the sound source is quite low, generally only a few ohms or even 1 ohm, the sound source of the volt-security curve close to the ideal voltage source.

4) Amplifier: audio signal frequency fixed under the premise of the amplifier can be seen as a linear active four-terminal network. The actual amplifier beats headphones cheap can be viewed as two power supplies with internal resistance, limited operating range, where the output voltage is proportional to the voltage at the input terminal within a certain range. It should be noted that for the four-terminal network, from the input to see the impedance can be seen from the output and the impedance is not the same. In order to improve the efficiency of energy use, while reducing the impact on the sound source, the amplifier input impedance is quite high, generally have more than ten thousand euros or even tens of thousands of euros. Therefore, the V-ampere characteristic curve at the input of the amplifier is close to the ideal current source.

The output impedance of the amplifier should also be as small as possible, but the output impedance of the amplifier is adjustable due to the need to adjust the volume. Adjust the size of the output impedance, you can change the headphone volume. Assuming that the input voltage is Uo and the amplification factor is A, the maximum voltage at the output is AUo. The volt-ampere characteristic curve at the output of the amplifier is a series of straight lines passing through a fixed point on the Y-axis.

5) headphones: the assumption that the sound source signal frequency fixed under the premise of the headset can be seen as a linear passive two-terminal network, equivalent to a resistance. Headset's volt-ampere characteristic curve and resistance, is a straight line through the origin. According to the different principles of sound, headphones can be divided into moving coil, piezoelectric and static three (static headphones basically did not contact, not discussed). The principle of moving the headset is to put the live coil in the magnetic field, the coil in the magnetic field force, thus driving the diaphragm sound. The magnitude of the force applied by the live coil in the magnetic field is proportional to the current flowing through the coil, and the greater the current, the greater the force. The principle of piezoelectric headphones is to apply voltage on both sides of the piezoelectric material to cause deformation of the piezoelectric material, thereby driving the diaphragm sound. The degree of deformation of the piezoelectric material is proportional to the voltage on both sides, the greater the voltage, beats by dre studio the greater the deformation.

Then you can look at a complete headset system.