A microphone is a transducer that converts sound waves into electrical signals, with types including measurement microphones for precise sound quantification and acoustic microphones for general audio applications. Measurement microphones are calibrated for use in fields such as acoustics research, while acoustic microphones are optimized for recording and broadcasting.
A microphone is a transducer that converts sound waves into electrical signals. The basic principle of a microphone involves the movement of a diaphragm in response to sound pressure. This movement is then converted into an electrical signal through various mechanisms depending on the microphone type. The resulting signal is a representation of the sound wave in an electrical format, which can then be processed by audio or measurement equipment. Microphones can broadly be categorized into two main groups based on their applications: measurement microphones and acoustic (or general-purpose) microphones.
Microphones for measurements:
Microphones for acoustic recordings:
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. Measuring microphones are used by audio engineers, acousticians, and researchers who rely on these devices for precise sound measurements in various fields.
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.
Pressure microphones are designed to have a uniform frequency response to the actual 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 cavities, such as coupler measurements and audiometer calibrations. They are also used for measurements at walls or surfaces, where the microphone can be mounted flush with the surrounding surface.
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.
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 microphones are designed to detect very low-frequency sounds, typically below 20 Hz. These microphones are used for monitoring natural phenomena such as earthquakes and volcanic activity, studying atmospheric conditions, and industrial monitoring. They usually come in larger sizes, typically around 1 inch, to effectively detect low-frequency sounds.
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 usually smaller, around 1/4 inch, to accurately capture high-frequency sounds. Understanding the different types of microphones and their specific applications helps in selecting the right microphone for accurate sound level measurements or high-quality audio recordings.
A MIRE microphone, short for Microphone In Real Ear, is a specialized microphone used in the field of audiology and hearing aid fitting. These microphones are designed to measure the sound pressure level inside the ear canal of a person wearing a hearing aid or earphone. The purpose of MIRE measurements is to understand how the hearing aid or earphone modifies the sound reaching the eardrum, allowing audiologists to fine-tune the device for optimal performance and comfort
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.
The main characteristics of a microphone include:
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:
Microphone Classifications:
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).
A microphone’s characteristics are influenced by construction, 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.
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.
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.
Temperature changes can affect the sensitivity of measuring microphones. High-quality microphones are designed to minimize these effects, ensuring consistent performance across a range of temperatures. Increased ambient pressure decreases a microphone’s sensitivity, quantified by the ambient pressure coefficient, which helps adjust measurements accordingly. Understanding and compensating for these effects maintain accurate sound measurements despite environmental changes.
Using a measurement microphone involves several steps for accurate sound measurements:
A microphone preamplifier is an electronic device used in the signal path between a microphone and input boards or recording equipment. They serve to amplify weak microphone signals to a level that can be effectively processed and analyzed, ensuring high-quality sound reproduction and accurate sound measurements. Their role is vital in maintaining signal integrity, reducing noise, and providing the necessary gain for various audio and measurement tasks.
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.
If a prepolarized microphone receives the wrong polarization voltage, it will not be damaged, but its sensitivity will change. These microphones are designed to operate without an external polarization voltage because they contain a built-in electret material that holds a permanent charge. Applying an incorrect voltage can affect the microphone’s performance, leading to inaccurate sound measurements.
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.
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.
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.
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.
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.
An authorized SVANTEK consultant will help You with the details such as the required accessories for your noise monitoring task.
