1. Capacitive Microphone
The core component of a condenser microphone is the electrode head, which consists of two thin metal films. When sound waves cause it to vibrate, the difference in the spacing between the metal films creates a difference in capacitance, generating a current. Because the electrode head requires a certain voltage for polarization to function, condenser microphones generally require phantom power. Condenser microphones are characterized by high sensitivity and high directivity. Therefore, they are commonly used in various professional music and film recordings and are frequently seen in recording studios. Another type of condenser microphone is the electret microphone. Electret microphones are characterized by their small size, wide frequency range, high fidelity, and low cost, and are widely used in communication equipment, home appliances, and other electronic products. During the manufacturing process, the diaphragm of an electret microphone is already subjected to high-voltage polarization, permanently carrying a certain charge, thus eliminating the need for an additional polarization voltage. For portability, electret condenser microphones can be made very small, which may affect sound quality to some extent. However, theoretically, the sound quality of an electret microphone of the same size and a traditional condenser microphone widely used in recording studios should not be significantly different.
The sound pickup principle of a condenser microphone is to use an extremely thin gold-plated diaphragm as one electrode of the capacitor, separated from it by zero points.
A few millimeters in diameter, with another fixed electrode, forms a capacitor of a few petawatts (pF). The thin-film electrode vibrates with the sound wave, causing a change in capacitance and generating an electrical signal. Because this capacitor is only a few pF, its internal resistance is extremely high, reaching the gigawatt (G) level. Therefore, a circuit is needed to convert this G G impedance to a more common impedance of around 600 ohms. This circuit, also called a "pre-amplifier circuit," is usually integrated inside the condenser microphone and requires "phantom power" to power it. It is because of this pre-amplifier circuit that condenser microphones require phantom power to function properly. Condenser microphones with phantom power generally have very high sensitivity, much higher than commonly used dynamic microphones. In other words, phantom power is essential for condenser microphones, whether used on a computer or other devices for recording, and the recorded sound is no quieter than that of a dynamic microphone.
II. Does a condenser microphone always need phantom power?
Condenser microphones do not necessarily require phantom power.
Some condenser microphones are powered by internal batteries, while others receive power via a signal cable from the mixing console or preamplifier they are connected to. Phantom power, also known as simplex powering, typically provides 11 to 48 volts of DC, simultaneously powering the polarization and amplification circuitry of the condenser head. Various condenser microphones draw between 1 and 12 milliamps of current. Many modern condenser microphones can tolerate voltages from 9 to 54 volts, as they incorporate internal rectifiers to accommodate a wide voltage range.
Phantom power requires a balanced connection between the microphone and the power supply. It typically uses the three wires of an XLR connector, with pins 2 and 3 supplied with the same DC voltage relative to pin 1 (ground). Generally, phantom power is supplied by AC mains power; battery power is only considered in areas without AC power, such as in the field.
III. How to use phantom power
A microphone designed for T-power only can be used with T-power power. Connecting a T-power microphone to regular phantom power will damage the microphone, the power supply, or both. Connecting a microphone designed for regular phantom power to a T-power supply will also result in poor performance. Because there are several different ways phantom power is implemented, strange phenomena can sometimes occur. At the most basic level, phantom power supply to the microphone input can be categorized into two main types: transformer-coupled and transformerless-coupled.
Transformer coupling typically uses a center-tapped winding. Phantom power is supplied to the tap through a resistor, ensuring that pins 2 and 3 at both ends of the winding receive the same voltage. [Figure 1]
Figure 2 illustrates that to maintain a zero potential difference between pins 2 and 3, the error between the two resistors must not exceed 1%.
Because there is no actual standard specification for the implementation of phantom power, and microphone manufacturers do not provide a product compatibility catalog, it is usually only through trial and error that one can find out.
Mixing consoles often have a phantom power switch that controls a group (e.g., 8) of input jacks. You need to know what happens if other types of microphones (e.g., dynamic microphones) are used simultaneously. Normally, dynamic microphones output signals from pins 2 and 3; even with phantom power on, the potentials on both pins are equal, and they function perfectly normally.
Do not connect condenser microphones with internal power to phantom power. Also, do not connect tube condenser microphones to phantom power; they require higher voltage and current and are typically supplied with dedicated power supplies.
If you try to connect a ribbon microphone to a phantom-powered outlet, you'll immediately run into big trouble; the poor ribbon will then become a fuse. Never plug a ribbon microphone into a phantom-powered outlet!
It's a good idea to regularly check and maintain your microphone cable and plug, otherwise intermittent or unstable phantom power can cause signal degradation or even noise.
