From the outside, a measurement microphone looks deceptively simple. But in real-world engineering, its interface options are surprisingly diverse: Lemo, BNC, Microdot, 10-32 UNF, M5, SMB… Many newcomers to acoustics ask questions like: Why can’t microphone interfaces be standardized? Why are cables often not interchangeable between microphones? What power and signal schemes are hidden behind different connectors? This article provides a structured overview of common measurement microphone interfaces, looking at physical connectors, powering methods, cable characteristics, and typical application-driven selection. Main Physical Interfaces for Measurement Microphones Below is a connector-by-connector summary, including the typical powering approach for each. Lemo (5-pin, 7-pin): The Classic Solution for Externally Polarized Microphones Lemo is a precision circular multi-pin connector and is the most common choice for externally polarized measurement microphones. The Lemo B series is widely used (e.g., 0B, 1B, 2B), and most standard measurement microphones adopt the Lemo 1B interface. Key Characteristics A multi-pin connector can carry multiple signals simultaneously, such as: Microphone output (analog signal) External polarization high voltage (typically 200 V) Preamplifier power supply Calibration/identification signals Additional benefits: Very reliable mechanical locking Well-suited for lab environments, metrology, and semi-anechoic chamber measurements where stability and traceability matter Notes on External Polarization Common polarization voltage is 200 V; some systems support switching between 0 V / 200 V Polarization voltage stability affects microphone sensitivity; in engineering practice, sensitivity variation is often treated as approximately proportional to voltage variation The preamplifier is typically powered separately (up to 120 V) but delivered via the same multi-pin connector Maximum output voltage can reach 50 Vp Includes pins for charge injection methods Separate output and ground paths help achieve lower noise In metrology labs, type testing, acoustic calibration, and high-precision semi-anechoic chamber work, the combination of “externally polarized microphone + Lemo multi-pin connector” is essentially a standard configuration. When not to use Lemo: Harsh environments with heavy contamination, oil exposure, and salt spray High costs of cables and connectors require careful trade-offs in field engineering applications BNC: The Most Common External Connector for IEPE Microphones Names like IEPE / ICP / CCP refer to the same general technology route: constant-current powering, where power and signal are transmitted on the same line (Constant Current Powering). In this system, the most common physical connector is the coaxial BNC. Interface and Powering Characteristics Coaxial structure, ideal for analog voltage transmission Bayonet lock (quick and reliable plug/unplug) Supports longer cable runs with good noise immunity Low cost and highly universal Typical IEPE Powering Parameters Constant current: 2–20 mA (common settings include 2 mA, 4 mA, 8 mA, etc.) Compliance voltage (supply capability): typically 18–24 V Maximum output voltage: generally around 8 Vp If the constant current is too low or the compliance voltage is insufficient, the maximum output signal swing is limited—directly affecting the maximum measurable SPL and the linear measurement range. In everyday testing such as engineering noise measurements, NVH, and environmental noise work, “IEPE microphone + BNC” has become the de facto standard. When not to use BNC: Applications requiring long-distance transmission of high-frequency signals, where signal attenuation becomes significant Applications involving frequent plugging and unplugging, to avoid an increased risk of poor electrical contact Microdot (10-32 UNF / M5): Lightweight Connectivity for Small Microphones Microdot is a threaded miniature coax connector widely used for small sensors (compact measurement microphones, accelerometers, etc.). It commonly uses a 10-32 UNF thread. What “10-32 UNF” Really Means This is simply an imperial fine-thread standard: Nominal diameter: 0.19 inch ≈ 4.826 mm Pitch: 1/32 inch ≈ 0.7938 mm Because 10-32 UNF is the typical thread used on Microdot connectors, the term “10-32 UNF” is often used informally to refer to the Microdot interface itself. What about M5? M5 is a metric thread standard: Nominal diameter: 5 mm Pitch: 0.8 mm Its dimensions are close to 10-32 UNF, and when tolerances are not extremely strict it can serve as a substitute—commonly seen in accelerometers or vibration microphones. Interface Characteristics Very compact; ideal for lightweight setups Threaded locking provides strong mechanical stability Commonly paired with IEPE powering Best for short runs and high-speed signal transmission When microphones must be placed in tight spaces, or where sensor mass/size is critical, Microdot is a common choice for compact, high-density installations. When not to use Microdot: Applications requiring quick connect/disconnect or frequent sensor replacement Use in systems with low constraints on installation space and requiring large-size connectors or high-power transmission, to avoid increased connection complexity and cost SMB (SubMiniature B): For High-Density Multi-Channel or Internal Connections SMB is a small “push-on” coaxial connector. Interface Characteristics Compact size supports high channel density Push-on structure enables fast connection Better high-frequency performance than BNC More suitable for semi-permanent internal wiring SMB is often best viewed as an engineering connector used inside equipment, rather than a field-plugging standard. When not to use Microdot: Applications involving frequent plugging and unplugging or repeated mechanical stress Use as a front-end connection interface for external devices, to avoid structural damage and reduced reliability Extended Interface Function: TEDS and Smart Identification In multi-channel and integrated systems, TEDS (Transducer Electronic Data Sheet) is increasingly common. By integrating a small memory chip into the sensor or cable, TEDS can store: Model and serial number Sensitivity Calibration date and other parameters Compatible front-end hardware or acquisition software can automatically read TEDS to: Identify the sensor type on each channel Load sensitivity and calibration coefficients automatically Reduce manual entry errors Save calibration time and labor At the connector level, TEDS is typically implemented by using certain pins in multi-pin Lemo connectors, or via overlay methods in specific BNC-based solutions. When planning an interface system, it’s wise to consider early on whether TEDS support is required. Why Are There So Many Interfaces? Connector diversity is best explained from three perspectives: Different Polarization and Powering Schemes Externally polarized microphones (≈ 200 V polarization) → better suited to multi-pin connectors like Lemo Prepolarized + IEPE systems → better suited to coaxial connectors like BNC / Microdot / SMB Different Scenarios and Priorities Laboratory / metrology: high stability, multiple signals in one cable, secure locking → Lemo Field engineering / environmental measurement: convenient wiring, strong universality → BNC + IEPE Miniaturization / high-density arrays: size and channel density first → Microdot / SMB Long Product Lifecycles and Backward Compatibility Measurement systems often have lifecycles of 10–20 years or more To avoid forcing users to replace large numbers of cables and front-end systems, manufacturers typically continue existing interface ecosystems Under long lifecycle constraints, “full unification” is often impractical and offers limited engineering return Typical Application Mapping (Quick Reference) Engineering noise, NVH, vibration/noise tests: BNC / MicrodotEasy wiring, many channels, low maintenance cost Precision lab measurement, type testing, metrology calibration: Lemo 7-pin / 5-pinSupports polarization HV and multiple signals; suitable for traceable high-precision measurement Acoustic arrays, multi-channel acquisition card systems: Microdot / SMBHigh channel density, compact wiring, easier system integration Long-term environmental noise monitoring systems: BNC / customized protected connectorsFocus on weather resistance, waterproofing, salt fog resistance, and stable long-distance transmission Conclusion The variety of measurement microphone interfaces is mainly the result of trade-offs between technology routes, application requirements, and historical compatibility—not simply a “lack of standards”. Taking NVH testing as an example: if an existing system uses BNC connectors to connect accelerometers, high-frequency signal attenuation and intermittent contact issues may occur in multi-channel array measurements. To improve connection reliability and signal quality, LEMO connectors with locking mechanisms and superior vibration resistance should be selected. After replacement, signal transmission stability is significantly improved, noise interference is reduced, and the consistency of test data is enhanced. You are welcome to learn more about microphone functions and hardware solutions on our website and use the “Get in touch” form to contact the CRYSOUND team.

A measurement microphone is not just any microphone — it is a precision acoustic sensor designed for traceable, repeatable sound pressure measurement. This guide covers how they work, the different types available, key specifications to compare, and how to select the right one for your application. What Is a Measurement Microphone? A measurement microphone is a high-precision acoustic transducer engineered to convert sound pressure into an electrical signal with known accuracy. Unlike studio or consumer microphones that are designed to make audio "sound good," a measurement microphone is designed to be truthful — its output must faithfully represent the actual sound pressure at the measurement point. The defining characteristics of a measurement microphone include: Known, stable sensitivity (expressed in mV/Pa) that can be traced to national or international standards Flat, well-characterized frequency response under defined sound-field conditions Wide dynamic range with low distortion from noise floor to maximum SPL Traceable calibration using pistonphones or acoustic calibrators Environmental stability — minimal drift due to temperature, humidity, and atmospheric pressure changes In practical terms, a measurement microphone is the front-end sensor of a metrology-grade measurement chain. Every specification — from the data acquisition system to the analysis software — depends on the microphone providing an accurate representation of the acoustic environment. For a deeper comparison between measurement and regular microphones, see our article: Differences Between Measurement Microphones and Regular Microphones. How Measurement Microphones Work The Condenser Principle How a condenser measurement microphone converts sound pressure into an electrical signal Nearly all measurement microphones are condenser (capacitor) microphones. The core transduction mechanism is simple but elegant: A thin metallic diaphragm is stretched in front of a rigid backplate, separated by a small air gap The diaphragm and backplate form a capacitor When sound pressure deflects the diaphragm, the gap changes, altering the capacitance With a constant charge on the capacitor, the capacitance change produces a proportional voltage change This voltage change is the microphone's output signal. A preamplifier, typically located immediately behind the capsule, converts the high-impedance signal from the capacitor into a low-impedance signal that can travel through cables to the data acquisition system. Polarization: External vs. Prepolarized Externally polarized (left) vs. prepolarized electret (right) microphone types The condenser principle requires a polarization voltage to maintain a charge on the capacitor. There are two approaches: Externally polarized microphones receive their polarization voltage (typically 200V) from an external power supply through the preamplifier. These microphones are considered the gold standard for the highest-accuracy laboratory measurements because:- The polarization voltage is stable and well-defined- No aging effects from the polarization source- Best long-term stability Prepolarized (electret) microphones use a permanently charged PTFE (Teflon) layer on the backplate to maintain polarization. Advantages include:- No external polarization supply needed — simplifies the signal chain- More resistant to humidity (no risk of charge leakage at high humidity)- Better suited for field measurements and harsh environments- Modern prepolarized microphones achieve accuracy comparable to externally polarized models FeatureExternally PolarizedPrepolarizedPolarization sourceExternal 200V supplyBuilt-in electret layerBest forLab/reference measurementsField and industrial useHumidity toleranceSensitive above ~90% RHExcellent, even in high humidityLong-term stabilityExcellentVery good (modern designs)Signal chainRequires compatible power supplyWorks with standard IEPE/ICP preamplifiers The Preamplifier The preamplifier is a critical but often overlooked component. It serves two functions: Impedance conversion: Transforms the microphone's extremely high output impedance (~GΩ) into a low impedance suitable for cable transmission Signal conditioning: Provides the power for IEPE/ICP operation or the polarization voltage for externally polarized capsules A matched microphone-preamplifier set ensures optimal performance. This is why measurement microphones are often sold as complete sets with a matched preamplifier — the combined system is calibrated and characterized as a unit. Types of Measurement Microphones Measurement microphones are classified along two primary axes: sound-field type and physical size. By Sound-Field Type The choice of microphone type depends on the acoustic environment where measurements will be taken. Free-Field Microphones A free-field microphone is designed to measure sound arriving from a single direction in an environment free of reflections (such as an anechoic chamber or outdoors). The microphone's frequency response is compensated for the acoustic diffraction effects caused by its own physical presence in the sound field. When to use: Outdoor measurements, anechoic chamber testing, source identification, environmental noise monitoring, any scenario where sound arrives predominantly from one direction. Orientation: Point the microphone directly at the sound source (0° incidence). Pressure-Field Microphones A pressure-field microphone measures the actual sound pressure at a surface or in a sealed cavity. It has the flattest possible response when the sound field is uniform across the diaphragm — which occurs in small cavities, couplers, or at surfaces where the microphone is flush-mounted. When to use: Coupler measurements (headphone and earphone testing), hearing aid testing, measurements in small cavities, flush-mounted surface measurements, acoustic impedance measurements. Orientation: The microphone diaphragm is placed at or within the measurement surface. Random-Incidence Microphones A random-incidence (diffuse-field) microphone is optimized for environments where sound arrives from all directions simultaneously — such as reverberant rooms. Its frequency response is a weighted average of responses at all angles of incidence. When to use: Reverberation chamber measurements, environmental noise in reflective spaces, any situation where sound arrives from multiple directions. Microphone TypeSound FieldTypical ApplicationOrientationFree-fieldSound from one directionOutdoor noise, anechoic testing, source IDPoint at sourcePressure-fieldUniform pressure (cavity)Coupler testing, headphones, hearing aidsFlush with surfaceRandom-incidenceSound from all directionsReverberant rooms, diffuse environmentsAny orientation Three microphone types for different acoustic environments: free-field, pressure-field, and random-incidence By Physical Size Measurement microphone capsules come in three standard sizes, each with distinct trade-offs: 1-Inch Microphones The largest standard size. High sensitivity and low noise floor make them ideal for measuring very quiet environments. Sensitivity: ~50 mV/Pa (highest) Frequency range: Up to ~8–16 kHz Best for: Low-frequency and low-level measurements, environmental noise monitoring, building acoustics Limitation: Large size limits upper frequency range due to diffraction effects 1/2-Inch Microphones The most widely used size. Offers a good balance between sensitivity, frequency range, and physical size. Sensitivity: ~12.5–50 mV/Pa Frequency range: Up to 20–40 kHz Best for: General-purpose acoustic measurements, NVH testing, product R&D, sound level meters Why it's popular: Versatile enough for most applications; fits standard sound level meter bodies 1/4-Inch Microphones The smallest standard size. Low sensitivity but the widest frequency range. Sensitivity: ~1.6–16 mV/Pa Frequency range: Up to 40–100 kHz Best for: High-frequency measurements, ultrasonic applications, small coupler measurements, acoustic array elements Trade-off: Higher noise floor requires louder sound sources for accurate measurement Size comparison: 1-inch (CRY3101), 1/2-inch (CRY3203), and 1/4-inch (CRY3401) measurement microphone capsules SizeSensitivity (typical)Frequency RangeDynamic RangeBest For1 inch50 mV/Pa4 Hz – 16 kHz15–146 dBALow-frequency, quiet environments1/2 inch12.5–50 mV/Pa3 Hz – 40 kHz16–164 dBAGeneral-purpose, NVH, SLM1/4 inch1.6–16 mV/Pa4 Hz – 100 kHz32–174 dBAHigh-frequency, ultrasonic, arrays Key Specifications Explained When comparing measurement microphones, these specifications matter most: Sensitivity Sensitivity defines how much electrical output the microphone produces for a given sound pressure. Expressed in mV/Pa (millivolts per Pascal) or dB re 1V/Pa. Higher sensitivity = better signal-to-noise ratio at low sound levels Lower sensitivity = higher maximum SPL before distortion There is always a trade-off between sensitivity and maximum SPL Frequency Response The frequency range over which the microphone provides accurate measurements, typically specified within ±2 dB or ±1 dB. The useful range depends on:- Microphone size (smaller = wider range)- Sound-field type (free-field compensation extends the useful range)- Mounting configuration Dynamic Range The span between the lowest measurable level (noise floor) and the highest level before a specified distortion threshold (typically 3% THD). A wider dynamic range means the microphone can handle a greater variety of measurement scenarios. Self-Noise (Equivalent Noise Level) The inherent electrical noise of the microphone, expressed as an equivalent sound pressure level in dBA. Lower is better — critical for measuring quiet environments. 1-inch microphones: ~15–18 dBA (quietest) 1/2-inch microphones: ~16–28 dBA 1/4-inch microphones: ~32–46 dBA Stability and Temperature Coefficient Long-term sensitivity drift and sensitivity change with temperature. Important for:- Permanent monitoring installations (fixed outdoor microphones)- Measurements in extreme environments (engine test cells, climatic chambers)- Ensuring measurement results are comparable over months or years IEC Standards Compliance Measurement microphones are classified according to IEC 61094 series:- IEC 61094-1: Primary calibration by reciprocity method- IEC 61094-4: Specifications for working standard microphones (laboratory use)- IEC 61094-5: Working standard microphones for in-situ (field) use Sound level meters incorporating measurement microphones must comply with:- IEC 61672-1: Class 1 (precision) or Class 2 (general purpose) How to Choose the Right Measurement Microphone How to select the right measurement microphone for your application Step 1: Identify Your Sound Field Your Measurement ScenarioRecommended TypeOutdoor environmental noiseFree-fieldAnechoic chamber testingFree-fieldHeadphone/earphone couplerPressure-fieldHearing aid testingPressure-fieldReverberant roomRandom-incidenceSurface-mounted on a machinePressure-fieldGeneral factory noiseFree-field or random-incidence Step 2: Determine Required Frequency Range ApplicationMinimum Frequency RangeBuilding acoustics20 Hz – 8 kHzEnvironmental noise20 Hz – 12.5 kHzGeneral acoustic testing20 Hz – 20 kHzNVH (automotive)20 Hz – 20 kHzElectroacoustic product testing20 Hz – 40 kHzUltrasonic measurements20 Hz – 100 kHz Step 3: Match the Dynamic Range to Your Environment Quiet environments (recording studios, anechoic chambers): Choose high-sensitivity microphones (50 mV/Pa, 1/2" or 1") with low self-noise Industrial environments (factory floors, engine test cells): Choose lower-sensitivity microphones (4–12.5 mV/Pa, 1/4" or 1/2") with high maximum SPL Wide-range applications: Choose microphones with the widest dynamic range available Step 4: Consider Environmental Conditions High humidity or outdoor use: Prepolarized microphones are recommended Extreme temperatures: Check the microphone's operating temperature range and temperature coefficient Dusty or wet environments: Look for IP-rated solutions (e.g., IP67 for NVH field testing) Hazardous areas: Check for ATEX/IECEx certification if required Step 5: Evaluate the Complete System A measurement microphone does not work alone. Consider:- Preamplifier compatibility: Matched sets ensure specified performance- Data acquisition system: Input impedance, voltage range, and sampling rate must match- Calibration infrastructure: Do you have access to a pistonphone or acoustic calibrator?- Software ecosystem: Can your analysis software import calibration data and apply corrections? Applications Electroacoustic Product Testing Testing loudspeakers, headphones, earphones, and hearing aids requires microphones that can accurately capture the device's frequency response, distortion, and directivity. Pressure-field microphones are used in couplers (IEC 60318 ear simulators), while free-field microphones are used in anechoic chambers. Automotive and Aerospace NVH NVH (Noise, Vibration, and Harshness) engineers use measurement microphones to characterize cabin noise, identify noise sources, evaluate sound packages, and perform transfer path analysis. Requirements include wide frequency range, high dynamic range, and robustness for field use. Environmental and Community Noise Monitoring Long-term outdoor noise monitoring stations require microphones with excellent stability over months or years, low temperature sensitivity, and tolerance to humidity, rain, and wind. Windscreens and weather protection accessories are essential. Production Line Quality Control In manufacturing, measurement microphones integrated into automated test systems verify that every loudspeaker, headphone, or microphone meets specifications before shipping. Speed, repeatability, and consistency are critical — the microphone must produce identical results across thousands of units per day. Building and Architectural Acoustics Measuring reverberation time, sound insulation, and HVAC noise requires accurate low-frequency performance and the ability to work in diffuse sound fields. Random-incidence microphones are often preferred. Acoustic Research and Standards Laboratories Primary and secondary calibration laboratories, standards organizations, and university research groups require the highest-accuracy microphones — typically externally polarized, laboratory-grade capsules calibrated by reciprocity methods. Sound Source Localization and Beamforming Microphone arrays used in acoustic cameras and beamforming systems require large numbers of measurement microphones with tightly matched sensitivity and phase response. 1/4-inch microphones are preferred for arrays due to their small size and wide frequency range. For more on acoustic imaging technology, see our guide on acoustic cameras. Noise Regulation Compliance Regulatory compliance measurements — workplace noise (ISO 9612), environmental noise (ISO 1996), product noise emission (ISO 3744/3745) — require Class 1 or Class 2 measurement microphones as specified in IEC 61672. Documentation of calibration traceability is mandatory for compliance reporting. CRYSOUND Measurement Microphone Solutions CRYSOUND's CRY3000 series measurement microphones cover the full range of sizes, field types, and applications — from laboratory reference measurements to rugged field testing. Complete Size Coverage: 1/4", 1/2", and 1" ModelSizeField TypeSensitivityFrequency RangeApplicationCRY3101-S011"Free-field50 mV/Pa4 Hz – 16 kHzLow-frequency, quiet environmentsCRY3203-S011/2"Free-field50 mV/Pa3.15 Hz – 20 kHzGeneral acoustic testingCRY3261-S021/2"Free-field450 mV/Pa10 Hz – 16 kHzUltra-high sensitivityCRY3201-S011/2"Free-field12.5 mV/Pa3.15 Hz – 40 kHzExtended high-frequencyCRY3401-S011/4"Free-field15.8 mV/Pa4 Hz – 40 kHzHigh-frequency testingCRY3403-S011/4"Free-field4 mV/Pa4 Hz – 90 kHzUltrasonic measurementsCRY3202-S011/2"Pressure12.5 mV/Pa3.15 Hz – 20 kHzCoupler and cavity testingCRY34021/4"Pressure1.6 mV/Pa4 Hz – 100 kHzHigh-frequency pressure fieldCRY3406-S011/4"Pressure15.8 mV/Pa4 Hz – 40 kHzLow-noise pressure field CRY3213: Purpose-Built for NVH The CRY3213 NVH Measurement Microphone is specifically designed for the demanding conditions of automotive and industrial NVH testing: IP67 protection: Fully dust-tight and submersible — operates reliably in engine bays, test tracks, and climatic chambers Extended temperature range: -50°C to 125°C, covering extreme hot and cold testing scenarios Free-field response: 3.15 Hz to 20 kHz, optimized for the frequency range relevant to cabin noise, powertrain NVH, and road noise 50 mV/Pa sensitivity: High enough for quiet cabin measurements, robust enough for engine noise Matched Microphone-Preamplifier Sets Every CRYSOUND measurement microphone set includes a matched preamplifier, factory-calibrated as a complete system. This eliminates the guesswork of mixing microphones and preamplifiers from different sources, and ensures that the combined frequency response, noise floor, and dynamic range meet the published specifications. Calibration and Traceability All CRYSOUND measurement microphones ship with individual calibration certificates traceable to national standards. For ongoing measurement assurance, see our guide on measurement microphone calibration. Explore CRYSOUND Measurement Microphones → Frequently Asked Questions What is the difference between a measurement microphone and a regular microphone? A measurement microphone is designed for accuracy and traceability — its output must truthfully represent the sound pressure at the measurement point. A regular microphone is designed for audio quality, often with intentional frequency shaping to enhance speech clarity or musical timbre. For a detailed comparison, read Measurement vs. Regular Microphones. Do I need to calibrate my measurement microphone? Yes. Regular calibration — at minimum before each measurement session using an acoustic calibrator — ensures your results are accurate and traceable. Periodic laboratory recalibration (typically annually) verifies long-term stability. Learn more about microphone calibration. Can I use a 1/2-inch microphone for ultrasonic measurements? Standard 1/2-inch microphones typically reach up to 20–40 kHz, which is insufficient for many ultrasonic applications. For measurements above 40 kHz, a 1/4-inch microphone is recommended — models like the CRY3403 reach 90 kHz, while the CRY3402 reaches 100 kHz. What does "free-field" vs. "pressure-field" mean? A free-field microphone is optimized for measuring sound arriving from one direction in open space. A pressure-field microphone is optimized for measuring sound pressure in enclosed cavities or at surfaces. The difference is in how the microphone compensates for acoustic diffraction effects at high frequencies. How do I choose between externally polarized and prepolarized? For laboratory reference measurements in controlled environments, externally polarized microphones offer the best long-term stability. For field measurements, industrial applications, or environments with high humidity, prepolarized microphones are more practical and equally accurate with modern designs. What IP rating do I need for outdoor or industrial use? For NVH field testing and outdoor measurements, IP67 (dust-tight, waterproof) provides the best protection. The CRY3213 is specifically designed for these conditions. For general lab use, IP protection is typically not required. Need help selecting the right measurement microphone for your application? Contact CRYSOUND for expert guidance based on your specific measurement requirements.