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- Transducer principles
The transducer principle in microphones describes the method by which acoustic sound signals are converted into electrical signals. This conversion occurs through the movement of a diaphragm set into motion by sound waves. The way this movement is translated into an electrical signal varies depending on the type of transducer principle used. Learn more...
- Receiver Principles
The receiver principle of microphones describes how they respond to sound from different directions. There are two main types. Learn more...
- Free Field/Diffuse Field Equalization
Free Field and Diffuse Field Equalization describe two different methods of adjusting the frequency response of a pressure receiver (a specific type of microphone) to achieve optimal results under various acoustic conditions:
1. Free Field Equalization:
In free field equalized microphones, the frequency response is optimized to be linear when sound directly hits the membrane (perpendicular to the membrane). This means that sound from a source directly impacting the microphone is captured as faithfully as possible. Therefore, free field equalized microphones are particularly suitable for close-miking situations where direct sound dominates.
2. Diffuse Field Equalization:
Diffuse field equalized microphones are designed to capture sound evenly from all directions. Their frequency response is adjusted so that in environments with a lot of reflection and reverb, where sound arrives at the microphone diffusely (from all sides), recordings are made as accurately as possible. Diffuse field equalization ensures that the sound in the space is not distorted when sound arrives from different directions simultaneously.
The frequency response of a microphone can be adjusted either through acoustic networks or through electrical filtering to make it free field or diffuse field equalized. Learn more...
- Proximity Effect
The proximity effect occurs in pressure gradient receivers (figure-eight, cardioid, supercardioid, hypercardioid). These microphones respond to the pressure difference between the front and back of their diaphragm. When a sound source is positioned very close to such a microphone, it results in an emphasis on the low frequencies in the recorded signal. This effect, also known as the "proximity effect," occurs because the pressure gradient that moves the microphone diaphragm is stronger in the near field of the sound source than in the far field.
The boost in low frequencies increases the closer the microphone is to the sound source and the lower the frequency of the sound. The proximity effect typically begins when the distance between the sound source and the microphone is smaller than the wavelength of the produced signal. This leads to lower tones being amplified compared to higher frequencies.
Microphones with a figure-eight pattern exhibit the strongest proximity effect, as they operate purely as pressure gradient receivers.
This effect is often intentionally utilized to make voices or instruments sound fuller and richer in bass, such as with vocal or close-microphone setups designed specifically for use near the sound source. However, the effect can be undesirable if it significantly alters the sound, which is why some microphones have mechanical or electronic measures to compensate for the bass boost, especially when recording speech.
In summary, the proximity effect arises from the physical property of directional microphones to amplify low frequencies in the near field, which is of great importance for sound and is deliberately used or controlled in many practical applications. Learn more...
- Phantom Power
Phantom power is a method of supplying power to condenser microphones through the microphone cable without the need for additional power lines. A DC voltage (typically 48V, but also 12V or 24V possible) is sent through the two signal conductors (pins 2 and 3 in an XLR connector) of the balanced cable to the microphone and is returned via the cable shield.
It is important that this voltage is present on both wires of the microphone's signal path without affecting the actual audio signal. Since there is no potential difference between the two signal conductors, other types of microphones, such as dynamic microphones, can also be used on the same connection without needing to turn off the phantom power.
This type of power supply is particularly widespread in professional audio technology because it is reliable, allows for simple wiring, and is minimally prone to interference. Learn more...
- Polar Pattern
The polar pattern of a microphone describes how it responds to sound from different directions. It is a graphical representation of a microphone's sensitivity concerning the direction of incoming sound. Omnidirectional microphones are sensitive all around, while microphones with cardioid or figure-eight patterns preferentially capture sound from specific directions and attenuate others. This is determined by the construction of the microphone, such as its orientation towards sound pressure or pressure gradient. The polar pattern affects how well a microphone can capture direct sound from a particular direction while rejecting diffuse sound from other directions, and it varies with frequency.
There are several main polar patterns that microphones can have, each with specific characteristics that affect sensitivity to sound from particular directions:
Omnidirectional Pattern:- Result of a pure pressure receiver
- A microphone with an omnidirectional pattern is sensitive all around and captures sound evenly from all directions.
- It is ideal for recording in acoustically balanced environments, as it equally captures both direct sound and ambient noise.
Figure-8 Pattern:- Result of a pure pressure gradient receiver
- Microphones with a figure-8 pattern are sensitive to sound from the front and back but have little sensitivity to sound from the sides.
- This pattern is often used in stereo or surround recordings, as it evenly captures sound from two opposing sides.
Cardioid Pattern:- This shape combines the omnidirectional and figure-8 patterns. Microphones with a cardioid pattern are primarily sensitive to sound from the front while significantly attenuating sound from the rear.
- They are well-suited for focusing on a sound source while simultaneously rejecting unwanted noise from behind.
Supercardioid and Hypercardioid Patterns:- These directional characteristics are developments of the cardioid pattern. The supercardioid captures sound even more tightly from the front and suppresses lateral sound more effectively than the cardioid but has less attenuation of rear sound.
- The hypercardioid is even more focused on the front and further reduces lateral sound but captures more sound from the rear than the supercardioid.
Wide Cardioid:- A broader version of the cardioid pattern that captures sound from a wider angle in front of the microphone. It is often used when a larger sound source or multiple sound sources need to be captured simultaneously in front of the microphone.
Shotgun (Directional Microphones):- Shotgun microphones have a very narrow directional response towards the front and are very effective at strongly attenuating sound from other directions. They are commonly used in film and television productions to accurately capture a sound source from a considerable distance.
Each polar pattern has specific applications depending on how much ambient noise should be attenuated and how much direct sound should be emphasized. Learn more...
- Shotgun Microphone / Interference Receiver
A shotgun microphone utilizes the interference effect to achieve a targeted directional characteristic. It features a tube with slots or openings along the axis in front of the diaphragm. Sound that strikes the tube at an angle is redirected by the openings in various directions and undergoes phase shifts, resulting in interferences that attenuate the sound. Only sound that hits parallel to the axis of the tube remains unfiltered and reaches the diaphragm unchanged. This creates a highly directional, shotgun-shaped characteristic. Shotgun microphones are typically condenser microphones and are available in various lengths for specific recording conditions. Learn more...
