What is a measurement microphone?

A measurement microphone is a calibrated transducer designed for devices that quantify sound, such as sound level meters. These microphones are engineered to meet standards such as IEC 61094, ensuring precise sound measurements. They are individually calibrated, with each calibration documented on a chart that serves as a vital reference throughout the microphone’s lifespan. Measurement microphones are known for their high accuracy, stability, and reliability, making them essential tools in fields such as acoustics research, environmental noise assessment, and audio equipment testing. They are used by audio engineers, acousticians, and researchers who rely on these devices for precise sound measurements in various fields.

What is an acoustic microphone?

An acoustic microphone is a transducer designed to capture sound waves for various audio applications, such as recording, broadcasting, and communication . Unlike measurement microphones, which are calibrated for precision and accuracy in sound quantification, acoustic microphones are optimized for general-purpose use, prioritizing qualities like frequency response, sensitivity, and durability. These microphones convert acoustic energy into electrical signals that can be amplified, recorded, or transmitted for playback, analysis, or communication. Acoustic microphones come in various types, including dynamic, condenser, ribbon, and MEMS, each suited for specific audio environments and requirements.

Microphone: Types, Characteristics, and Uses

A microphone is a transducer that converts sound waves into electrical signals. We distinguish between measurement microphones, designed for precise registration and measurement of sound levels, and acoustic microphones, intended for general audio applications. Acoustic microphones are used for recording or transmitting sounds, such as on stage, in recording studios, or during telephone and internet conversations. In contrast, measurement microphones are primarily utilized in acoustic research.

What are pressure microphones?

Pressure microphones are designed to have a uniform frequency response to the sound pressure present at the microphone diaphragm. They measure the sound pressure level directly, without compensating for the presence of the microphone in the sound field. Pressure microphones are primarily used in closed environments, such as coupler measurements, audiometer calibrations, or when mounted flush with a surface. These microphones are ideal for measuring sound in enclosed spaces where reflections and other acoustic factors are controlled.

What are free-field microphones?

Free-field microphones are designed to measure sound as it exist in an open space, without reflections or obstructions. These microphones account for how sound waves interact with the microphone body, providing a frequency response that compensates for these effects. Free-field microphones are commonly used in outdoor measurements or environments where an accurate representation of the sound source is required. They are widely used in sound level meters, with settings adjusted for either free-field or diffuse-field compensation depending on whether the measurement is indoor or outdoor.

What are random incidence microphones?

Random incidence microphones are designed for measuring in sound fields where sound waves come from multiple directions, such as in a reverberation chamber or highly reflective surroundings. The combined influence of sound waves from all directions depends on their distribution. For measurement microphones, a standard distribution based on statistical considerations has been defined, resulting in a standardized random incidence microphone. These microphones are recommended for sound pressure level measurements according to ANSI standards.

Infrasonic and ultrasonic microphones

Infrasonic microphones are designed to detect very low-frequency sounds, typically below 20 Hz. These microphones are used for applications such as monitoring industrial machinery (e.g., wind turbines) or detecting low-frequency environmental noise. Infrasonic microphones are usually larger, around 1 inch in diameter, to capture low-frequency sounds effectively.
Ultrasonic microphones, on the other hand, are designed to detect very high-frequency sounds, typically above 20 kHz. These microphones are used for applications such as detecting bat echolocation, ultrasonic flaw detection in materials, medical diagnostics, and industrial automation. They are generally smaller, around 1/4 inch, to accurately capture high-frequency sounds.

What is a MIRE microphone?

A MIRE microphone (Microphone In Real Ear) is a specialized microphone designed to measure the sound pressure level inside the ear canal. The purpose of MIRE measurements is to assess noise levels from sound sources located close to the ear, particularly headphones. Example applications include measurements in pilot helmets and call centers. Another important use is evaluating the effectiveness of hearing protection by measuring sound levels underneath protective earmuffs.

What is an outdoor and wireless microphone?

An outdoor and wireless microphone typically refers to a sound level meter with an integrated microphone designed for outdoor use and equipped with wireless transmission capabilities. These systems are enclosed in protective housings that shield the microphone from environmental elements such as wind and rain. The meters often include compensation filters to counteract the effects of the enclosure and foam protections on the microphone’s performance. The wireless feature allows the sound level meter to transmit audio data to a receiver or monitoring station without the need for physical cables, facilitating remote and continuous environmental noise monitoring.

What are the main microphone characteristics?

The main characteristics of a microphone include:

Sensitivity: It defines how effectively a microphone converts acoustic sound into an electrical signal, measured in millivolts per Pascal (mV/Pa). Alternatively, microphone manufacturers may provide sensitivity where the voltage is referenced in dB relative to 1 V, for example, 35 mV/Pa (-29 dBV/Pa), as in the case of the ACO 7052E.
Frequency Response: The range of frequencies a microphone can accurately reproduce.
Directional Pattern: Indicates the microphone’s sensitivity to sound from various directions.
Dynamic Range: The range between the quietest and loudest sound levels a microphone can accurately capture.
Noise Level: The inherent noise produced by the microphone’s electronics, usually measured in A-weighted decibels (dBA).

What is the microphone class?

According to the IEC 61094 standard, microphones are classified as either laboratory reference microphones or measurement microphones used in routine measurements. This standard uses specific abbreviations to denote the types and sizes of microphones:

LS (Laboratory Standards): Denotes laboratory reference microphones.
WS (Working Standards): Denotes measurement microphones used in daily routine measurements.

Microphone Classifications:

LS1P: Laboratory standard 1-inch pressure-field microphone.
LS2P: Laboratory standard 1/2-inch pressure-field microphone.
WS1F: 1-inch free-field working standard microphone.
WS2F: 1/2-inch free-field working standard microphone.
WS3F: 1/4-inch free-field working standard microphone.
WS1P: 1-inch pressure-field working standard microphone.
WS2P: 1/2-inch pressure-field working standard microphone.
WS3P: 1/4-inch pressure-field working standard microphone.

Therefore, there is no classification of microphones into Class 1 or Class 2; these classifications apply to sound level meters as per IEC 61672-1. The microphones themselves are classified according to the IEC 61094 standard as either laboratory reference microphones (LS) or working standard microphones (WS).

What influences a microphone’s characteristics?

The characteristics of a microphone are influenced by its design, operating principle, interference, placement, aging, and environmental conditions. Construction involves the design and materials used, which affect performance. Interference includes electromagnetic and mechanical vibrations that can introduce noise. Placement affects directional characteristics and frequency response. Aging impacts components like the diaphragm, altering sensitivity and frequency response. Environmental conditions such as temperature, humidity, and atmospheric pressure can also affect performance, requiring careful management to maintain accuracy.

What is microphone sensitivity?

Microphone sensitivity is a measure of how effectively a microphone converts acoustic sound pressure into an electrical signal. It is typically expressed in millivolts per Pascal (mV/Pa), indicating the voltage output produced by the microphone for a given sound pressure level. For example, if a microphone has a sensitivity of 50 mV/Pa, it means that for every Pascal of sound pressure (approximately the sound pressure level at about 94 dB), the microphone will produce an output signal of 50 millivolts. This value helps in determining how well the microphone will perform in different sound environments and how much amplification might be required for the desired application.

What is the microphone dynamic range?

The dynamic range of a microphone refers to the range between the lowest and highest measurable sound pressure levels it can accurately capture. A wide dynamic range is crucial because it allows the microphone to handle a broad spectrum of sound intensities, from very quiet sounds to extremely loud ones, without distortion or loss of detail.

How do temperature and ambient pressure affect measuring microphones?

Temperature changes can affect the sensitivity of measurement microphones. High-quality microphones are designed to minimize these effects, ensuring parameter stability across a wide temperature range. An increase in atmospheric pressure reduces the microphone’s sensitivity, which can be expressed by an atmospheric pressure coefficient that allows for proper measurement corrections. For example, as altitude increases, atmospheric pressure decreases, potentially increasing the microphone’s sensitivity. Conversely, in deep mines where pressure rises, the microphone’s sensitivity may decrease. It is important to account for these changes to maintain measurement accuracy.

How to use a measurement microphone?

Using a measurement microphone involves several steps for accurate sound measurements:

First, select the appropriate microphone type for your specific application, such as free-field, pressure, or random incidence. Ensure the microphone is calibrated by referencing its calibration chart.
Connect the microphone to a preamplifier, then to your sound level meter directly or using a high-quality cable.
Properly position the microphone, perform a calibration check using a known sound source, and begin recording data.
Consider environmental factors and use protective measures if necessary.
After measurements, store the equipment in a dry, controlled environment.

What is a microphone preamplifier?

A microphone preamplifier is an electronic device used in the signal path between the microphone and recording or measuring equipment. Its function is to convert/match the high internal impedance of the condenser microphone capsule to the requirements of the subsequent system components. This means that its role is to adjust the microphone signals to a level that can be effectively processed and analyzed. The preamplifier plays a key role in maintaining signal integrity and providing the appropriate gain for various tasks related to sound recording and measurement.

What is a microphone cable?

A microphone cable is an essential component in the audio and measurement signal chain, used to connect a microphone preamplifier to an input board or other audio equipment. These cables are designed to maintain signal integrity by minimizing noise and interference, ensuring that the audio signal is transmitted clearly and accurately. High-quality microphone cables typically feature shielding and balanced connections to further reduce the impact of external noise and electromagnetic interference.

What happens if a prepolarized microphone receives the wrong polarization voltage?

If a prepolarized microphone (electret) receives external polarization voltage, typically used for externally polarized microphones, it will not be damaged but its sensitivity may be affected. These microphones are designed to operate without external polarization, as they contain a built-in electret material that holds a permanent charge. Applying external voltage to a prepolarized microphone can lead to inaccurate sound measurements due to changes in performance.

Why is factory calibration important for measuring microphones?

Factory calibration is crucial for measuring microphones because it ensures the microphone’s accuracy and reliability right from the start. During factory calibration, each microphone is meticulously tested against precise standards to establish its exact sensitivity, frequency response, and other critical parameters. This process involves comparing the microphone’s performance with a known reference, allowing for any necessary adjustments to meet stringent accuracy requirements.

Why 94dB is used for microphone calibration?

94 dB is used for microphone calibration because it corresponds to a sound pressure level of 1 Pascal, which is a convenient reference point. This standard reference level provides a consistent and easily replicable baseline for measuring and comparing microphone sensitivity. Calibrating microphones at 94 dB ensures that their sensitivity ratings are standardized, allowing for accurate and reliable performance across various applications. By using this reference level, manufacturers and users can ensure that microphones produce a consistent output when exposed to a known sound pressure, facilitating precise sound measurements and maintaining uniformity in audio equipment testing and calibration. In practice, calibrators with a level of 114 dB are also used for calibration, especially when the acoustic background noise is high.

Why is periodic recalibration necessary for sound level meters with microphones?

Periodic recalibration of sound level meters with microphones, driven by regulations such as IEC 61672-3, is a proactive measure to ensure these devices remain accurate, reliable, and compliant with standards over their operational lifespan. This process is essential for maintaining the validity and precision of sound measurements in various professional and regulatory contexts. Regular recalibration helps verify performance, detect any drift, and ensure consistency in measurements, thus upholding the integrity of data collected for environmental noise monitoring, occupational health assessments, and other critical applications.

What is an electrostatic actuator?

An electrostatic actuator is a device used in the calibration of condenser microphones. It operates by applying an electrostatic force to the microphone’s diaphragm, simulating the effect of sound waves. This method allows for precise control and measurement of the microphone’s response to a known input, facilitating accurate calibration. The electrostatic actuator works by placing a rigid, conductive grid near the microphone diaphragm and applying an alternating voltage between them. This creates an electrostatic field that moves the diaphragm similarly to how sound pressure would. By varying the frequency and amplitude of the applied voltage, the frequency response and sensitivity of the microphone can be measured.

Who calibrates measurement microphones?

Microphones, particularly those used for precise measurements, are calibrated by laboratories accredited under ISO 17025 standards. These labs, such as Svantek, specialize in calibration and testing to ensure the accuracy and reliability of measurement instruments. ISO 17025 accreditation signifies that a laboratory meets international standards for technical competence and quality management, ensuring that the calibration results are accurate and traceable to recognized standards.

Microphone: Types, Characteristics, and Uses

What is a microphone?