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.

Acoustic cameras turn invisible sound into visible images. This guide explains how they work, where they're used, and how to choose the right one for your application. What Is an Acoustic Camera? An acoustic camera is a device that locates and visualizes sound sources in real time. It combines a microphone array — typically 64 to 200+ MEMS microphones arranged in a specific pattern — with a video camera and signal processing software. The result is a color-coded overlay on a live video feed, showing exactly where sound is coming from and how loud it is. Think of it as a thermal camera, but for sound instead of heat. Where a thermal camera shows hot spots in red, an acoustic camera shows loud spots — pinpointing the exact location of a leak, a faulty bearing, or an electrical discharge that you can't see with your eyes. The technology was originally developed for aerospace and automotive NVH (Noise, Vibration, and Harshness) testing. Today, it has expanded into industrial maintenance, energy utilities, manufacturing quality control, and building acoustics. How Does an Acoustic Camera Work? How an acoustic camera uses beamforming: sound waves arrive at each microphone with different time delays (Δt), the processor combines all signals, and outputs a color-coded sound map. The Microphone Array At the core of every acoustic camera is a microphone array — a precisely arranged set of MEMS (Micro-Electro-Mechanical Systems) microphones. The number of microphones directly affects performance: 64 microphones: Entry-level, suitable for general-purpose sound source localization 128 microphones: Professional-grade, better resolution and dynamic range 200+ microphones: High-end, capable of detecting subtle sources in noisy environments The spatial arrangement of these microphones matters as much as the count. Common configurations include circular, spiral (Fibonacci), and grid patterns. Each has trade-offs: spiral arrays offer good broadband performance, while grid arrays are better for near-field measurements. Beamforming: The Core Algorithm The key technology behind acoustic cameras is beamforming — a signal processing technique that combines signals from multiple microphones to "focus" on specific locations in space. Here's a simplified explanation: A sound wave arrives at each microphone at slightly different times (because each microphone is at a different distance from the source) The software calculates the expected time delay for every possible source location in the field of view For each candidate location, it shifts and sums the microphone signals according to the calculated delays Locations where the shifted signals add up constructively are identified as sound sources This process is repeated for every pixel in the image, producing a "sound map" that shows the spatial distribution of sound energy. Beamforming vs. Acoustic Holography There are two main acoustic imaging technologies: FeatureBeamformingAcoustic Holography (NAH)Best frequency rangeMid to high frequencies (>500 Hz)Low frequencies (<2 kHz)Measurement distanceFar-field (>1 meter)Near-field (<30 cm from source)ResolutionLimited by wavelength and array sizeHigher resolution at low frequenciesSpeedReal-time capableRequires careful scanningBest forLeak detection, general noise mappingEngine NVH, vibration analysis Most modern acoustic cameras use beamforming as the primary method because it works in real time and doesn't require the camera to be positioned close to the source. Some advanced systems support both technologies for maximum flexibility. The Role of the Video Camera The microphone array generates a sound map; the video camera provides the visual reference. The software overlays the sound map onto the video feed as a color-coded heat map, allowing the user to instantly see which component, pipe, or connection is producing the sound. High-end systems use depth cameras (such as Intel RealSense) to create 3D acoustic maps, enabling more accurate source localization on complex geometry. Frequency Range: Why It Matters Different applications require different frequency ranges: ApplicationTypical Frequency RangeWhyCompressed air leak detection20–50 kHzLeaks produce high-frequency hissingPartial discharge detection20–100 kHzElectrical discharges emit ultrasonic signalsMechanical fault detection1–20 kHzBearing wear, misalignment produce audible noiseAutomotive NVH100 Hz–10 kHzRoad noise, wind noise, engine noiseBuilding acoustics50 Hz–8 kHzLow-frequency structure-borne noise An acoustic camera with a frequency range of up to 100 kHz can handle virtually all industrial applications, including ultrasonic leak and partial discharge detection. Cameras limited to 20 kHz are suitable only for audible noise analysis. Key Applications Acoustic camera detecting vacuum leaks in composite materials — the color overlay pinpoints the exact leak location on the surface. Partial discharge detection on high-voltage insulators — the acoustic camera identifies discharge locations from a safe distance, combined with infrared thermal imaging for comprehensive diagnostics. 1. Compressed Air Leak Detection Compressed air is one of the most expensive energy sources in a factory. Studies show that 20–30% of compressed air is lost to leaks. An acoustic camera can scan an entire production line in minutes, identifying leaks that are invisible and inaudible to human ears. Why acoustic cameras beat traditional methods: Ultrasonic leak detectors require you to check one point at a time; an acoustic camera scans an entire area at once Visual overlay pinpoints the exact location — no guessing Many systems can estimate leak rate and annual cost, helping you prioritize repairs 2. Electrical Partial Discharge Detection Partial discharge (PD) is an early warning sign of insulation failure in high-voltage equipment — transformers, switchgear, cables, and bus bars. Left undetected, PD leads to complete insulation breakdown and potentially catastrophic failure. Acoustic cameras detect PD by capturing the ultrasonic emissions (typically 20–100 kHz) that accompany electrical discharge. The advantage over traditional PD detection methods: Non-contact: No need to de-energize equipment Real-time visualization: See exactly where the discharge is occurring Safe distance: Inspect live equipment from several meters away 3. Mechanical Fault Diagnosis Worn bearings, misaligned shafts, loose components, and valve leaks all produce characteristic sound signatures. An acoustic camera can identify and locate these faults before they lead to unplanned downtime. Common use cases: Motor and pump bearing wear detection Steam trap malfunction Valve leak identification Gearbox noise analysis 4. Automotive and Aerospace NVH Testing This is where acoustic cameras originated. NVH engineers use them to: Identify wind noise sources on vehicle bodies Locate rattles and squeaks in interior trim Analyze tire/road noise contributions Map engine noise radiation patterns Validate sound package effectiveness For NVH applications, large-aperture arrays (200+ microphones) provide the resolution needed to distinguish closely spaced sources. 5. Noise Compliance and Building Acoustics Environmental noise regulations require manufacturers to identify and reduce noise emissions. Acoustic cameras help: Map factory noise sources for compliance reporting Identify noise paths in buildings (walls, windows, HVAC) Verify effectiveness of noise barriers and enclosures 6. UAV-Mounted Acoustic Inspection A newer application: mounting acoustic cameras on drones for inspection of hard-to-reach infrastructure. Applications include: Power line and substation inspection Wind turbine blade inspection Pipeline corridor leak surveys Tall structure noise mapping Types of Acoustic Cameras Four form factors of acoustic cameras: Handheld (CRY8124), Fixed-Mount (CRY2623M), Large Array (CRY8500 SonoCAM Pi), and UAV-Mounted (CRY2626G). Handheld Acoustic Cameras Portable, battery-powered devices for field use. Typically 64–128 microphones with a built-in display. Best for maintenance rounds, leak detection, and quick inspections. Pros: Portable, easy to use, quick deployment Cons: Limited microphone count, smaller array = lower resolution at distance Fixed/Mounted Acoustic Cameras Permanently installed for continuous monitoring. Used in power substations, data centers, and critical infrastructure. Can run 24/7 with automated alerts. Pros: Continuous monitoring, automated alerting, no operator needed Cons: Fixed field of view, higher installation cost Large-Array Systems 200+ microphones on a larger frame. Used for NVH testing, pass-by noise measurement, and research applications. Often mounted on tripods or overhead structures. Pros: Highest resolution, widest frequency range, best for complex analysis Cons: Not portable, requires setup, higher cost UAV-Mounted Systems Lightweight acoustic arrays designed for drone mounting. Used for remote inspection of power lines, pipelines, and industrial facilities. Pros: Access to hard-to-reach locations, large-area surveys Cons: Flight time limits, vibration interference, regulatory requirements How to Choose the Right Acoustic Camera Quick decision guide: Choose your acoustic camera based on primary application. Step 1: Define Your Primary Application Your application determines the minimum specifications: ApplicationMin. MicrophonesFrequency RangeForm FactorCompressed air leak detection64Up to 50 kHzHandheldPartial discharge detection64–128Up to 100 kHzHandheld or fixedMechanical fault diagnosis64Up to 20 kHzHandheldNVH testing128–200+100 Hz–20 kHzLarge arrayContinuous monitoring64–128Application-dependentFixedDrone inspection64–128Up to 50 kHzUAV-mounted Step 2: Consider the Environment Noisy factory floor? You need more microphones and advanced algorithms to separate the target signal from background noise Outdoor use? Look for weather-resistant designs and wind noise rejection Hazardous area? Check for ATEX/IECEx certification Large distance? More microphones = better resolution at range Step 3: Evaluate the Software The hardware captures the data; the software turns it into actionable information. Key software features to look for: Real-time display: See the sound map live as you scan Frequency filtering: Isolate specific frequency bands to focus on particular issues Leak rate estimation: Quantify the cost of leaks in dollars or energy units Reporting: Generate professional reports with screenshots, measurements, and recommendations AI-assisted detection: Automatic identification of leak patterns and fault signatures Step 4: Compare Specifications Key specs to compare across manufacturers: SpecificationWhat It MeansWhat to Look ForMicrophone countMore mics = better resolution and sensitivity64 minimum; 128+ for demanding applicationsFrequency rangeDetermines what you can detectUp to 100 kHz for PD and ultrasonic leaksDynamic rangeAbility to measure both quiet and loud sources>70 dB for industrial environmentsAngular resolutionAbility to separate nearby sourcesSmaller is better; depends on frequency and distanceFrame rateHow quickly the sound map updates>10 fps for real-time scanningWeight and sizePortability<2 kg for handheld daily-use devicesBattery lifeRuntime for field use>3 hours for a full shift of inspectionsIP ratingDust and water resistanceIP54 or higher for industrial environments CRYSOUND Acoustic Camera Solutions CRYSOUND offers one of the widest product lines in the acoustic camera market — covering handheld, fixed-mount, large-array, and UAV-mounted form factors from a single manufacturer. Product Lineup CRY2624: 128-microphone handheld acoustic camera with ATEX certification — portable, field-ready, and safe for hazardous environments CRY8124: 200 MEMS microphones, frequency range up to 100 kHz — handles both audible noise analysis and ultrasonic applications (leak detection + partial discharge) in a single device CRY2623M: Fixed-mount version for 24/7 continuous monitoring of substations and critical infrastructure CRY8500 Series (SonoCAM Pi): Large spiral microphone array for NVH testing, pass-by noise measurement, and advanced acoustic research CRY2626G: Drone-mounted acoustic camera for remote inspection of power lines, pipelines, and wind turbines CRYSOUND acoustic camera product family: from handheld to drone-mounted solutions. Key Differentiator 1: Modular Sensor Expansion Unlike most competitors that offer a fixed-function device, CRYSOUND's acoustic cameras support external sensor modules for expanded capabilities: Infrared thermal imaging module: Combines acoustic and thermal data in a single view — when inspecting power equipment, engineers can simultaneously see the acoustic signature of partial discharge and the thermal hot spot of overheating components. This dual-mode inspection is widely used in power utilities for comprehensive substation diagnostics. IA3104 Contact Ultrasound Sensor: An external contact-type ultrasonic probe designed specifically for valve internal leak detection. The sensor couples directly to the metal surface of a valve, capturing high-frequency ultrasonic signals generated by internal leakage. Combined with intelligent analytics and guided workflows, it automates the full diagnostic process — from data acquisition to leak classification. This is critical for preventive maintenance of oil pipeline valves and natural gas network valves. This modular approach means a single CRYSOUND acoustic camera can serve as a comprehensive inspection platform, rather than requiring separate instruments for each detection task. Key Differentiator 2: Acoustic Link Mobile App CRYSOUND's Acoustic Link is a companion mobile app that connects to the acoustic camera via Wi-Fi. It enables: On-device preview: View captured photos, videos, and inspection reports on your phone or tablet — no PC required Defect-specific visualization: Retrieve gas-leak acoustic maps, partial-discharge patterns, and thermal images directly in the app One-tap sharing: Save results locally and share via the system share sheet for instant communication with colleagues and customers Automated report generation: Generate and export professional inspection reports from the field, eliminating the need to return to the office for post-processing For field inspection teams, this means faster turnaround from detection to documentation. Key Differentiator 3: Complete Acoustic Ecosystem Beyond acoustic cameras, CRYSOUND manufactures electroacoustic test systems (CRY6151B), acoustic test chambers, and calibration equipment — enabling complete acoustic testing solutions from a single vendor. With 28 years of experience and over 10,000 customers across 90+ countries, CRYSOUND brings deep domain expertise to every product. Explore CRYSOUND Acoustic Camera Products → Frequently Asked Questions What is the difference between an acoustic camera and a sound level meter? A sound level meter measures the overall sound pressure level at a single point. It tells you how loud it is, but not where the sound comes from. An acoustic camera shows both the location and the intensity of sound sources, making it far more useful for diagnosing and fixing noise problems. How far away can an acoustic camera detect a leak? Detection range depends on the leak size, background noise, microphone count, and frequency range. A typical handheld acoustic camera with 64–128 microphones can detect a 1mm compressed air leak from 10–30 meters away. Larger leaks can be detected from even greater distances. Can an acoustic camera work in a noisy factory? Yes. Modern acoustic cameras use beamforming algorithms that can isolate specific sound sources even in high-background-noise environments. The key is having enough microphones — more microphones provide better noise rejection and higher signal-to-noise ratio. Do I need training to use an acoustic camera? Basic operation is straightforward — point the camera, look at the screen, and identify the highlighted areas. Most users can start finding leaks within minutes. However, interpreting complex acoustic patterns (NVH analysis, partial discharge classification) benefits from training and experience. What is the ROI of an acoustic camera? For compressed air leak detection alone, the ROI is typically measured in months. A single quarter-inch air leak costs $2,500–$8,000 per year. Most industrial facilities have dozens to hundreds of leaks. An acoustic camera that helps you find and fix these leaks can pay for itself in the first survey. Can acoustic cameras detect gas leaks other than compressed air? Yes. Acoustic cameras can detect any pressurized gas leak that produces turbulent flow noise — including nitrogen, oxygen, hydrogen, natural gas, and refrigerants. The frequency characteristics may vary by gas type, but the detection principle is the same. Need help choosing the right acoustic camera for your application? Contact CRYSOUND for a personalized recommendation based on your specific requirements.

What Is an Anechoic Chamber? An anechoic chamber is a room designed to completely absorb sound reflections. The walls, ceiling, and (in a full anechoic chamber) the floor are lined with wedge-shaped foam or fibreglass absorbers that prevent sound waves from bouncing back into the room. The result is a controlled acoustic environment that simulates free-field conditions — as if the sound source were suspended in open air with no surfaces nearby. This matters because most acoustic measurements — sound power, directivity, frequency response — require a known, reflection-free environment to produce repeatable, standards-compliant results. Without it, room reflections contaminate the measurement, making results dependent on the specific room rather than the product being tested. Full Anechoic vs Semi-Anechoic (Hemi-Anechoic) Chambers Feature Full Anechoic Semi-Anechoic (Hemi-Anechoic) Absorbing surfaces All 6 surfaces (walls, ceiling, floor) 5 surfaces (walls + ceiling); floor is reflective Floor Wire mesh or perforated metal grid suspended above absorbers Solid, load-bearing concrete or steel Acoustic condition Free-field (no reflections from any direction) Free-field over a reflecting plane Load capacity Limited — cannot support heavy equipment directly Can support vehicles, machinery, industrial equipment Primary standards ISO 3745 (precision sound power) ISO 3744 (engineering sound power), ISO 3745 Typical use Microphone calibration, loudspeaker characterisation, hearing research Automotive NVH, product noise testing, industrial machinery Cost Higher (floor treatment adds significant cost and complexity) Lower (no floor treatment needed) In practice, about 80% of industrial acoustic testing uses semi-anechoic chambers because most test objects — cars, appliances, compressors, power tools — are too heavy for a suspended wire-mesh floor. What Standards Require an Anechoic Chamber? ISO 3745 — Precision Sound Power Measurement The gold standard for sound power determination. Requires either a full anechoic or hemi-anechoic chamber qualified to meet strict free-field deviation limits across the frequency range of interest. The chamber must demonstrate that the inverse-square law holds to within ±1 dB at the measurement positions. Typical cut-off frequency: 80–200 Hz, depending on chamber size and wedge depth. Below this frequency, the chamber no longer behaves as a free field. ISO 3744 — Engineering Sound Power Measurement Less stringent than ISO 3745 but still requires a hemi-anechoic environment. Allows for environmental corrections when the room is not perfectly anechoic, making it practical for production-floor test cells that approximate (but do not perfectly achieve) free-field conditions. ISO 26101 — Qualification of Free-Field Environments Defines how to verify whether a room actually meets free-field requirements. This is the standard used to “qualify” an anechoic or hemi-anechoic chamber — confirming that its acoustic performance matches what is claimed. Other Standards ECMA-74: IT equipment noise measurement (uses ISO 3745 or ISO 3744 as the underlying acoustic method) ANSI S12.55 / S12.56: North American equivalents of ISO 3744/3745 ISO 11201–11205: Various sound pressure level determination methods, some requiring free-field conditions Key Design Considerations 1. Chamber Size and Usable Volume The physical dimensions determine the lowest usable frequency. A general rule: the chamber must be large enough that the distance between the sound source and each measurement microphone is at least one wavelength at the lowest frequency of interest. For a 100 Hz cut-off, the minimum source-to-microphone distance is approximately 3.4 metres, which means the chamber’s internal dimensions (excluding wedges) should be at least 7–8 metres per side for a hemi-anechoic chamber. 2. Wedge Absorbers The depth of the absorbing wedges determines the low-frequency performance. Deeper wedges absorb lower frequencies: Wedge Depth Approximate Low-Frequency Cut-off 200 mm ~500 Hz 500 mm ~200 Hz 1000 mm ~80–100 Hz Wedge materials include melamine foam (lightweight, fire-retardant) and fibreglass (better low-frequency absorption but heavier). 3. Background Noise An anechoic chamber must also be well-isolated from external noise. The ambient noise level inside the chamber (with no source operating) should be at least 6 dB — and preferably 15 dB — below the sound pressure level generated by the test object at the measurement positions. This typically requires a chamber built with multiple layers of massive construction (concrete, steel) and vibration-isolated mounting to prevent structure-borne noise transmission. 4. Vibration Isolation For NVH testing (especially automotive), the chamber floor may include vibration-isolated foundations or air-spring mounting systems to prevent road-simulator or dynamometer vibrations from coupling into the acoustic measurement environment. What If You Do Not Have an Anechoic Chamber? Not every organisation can invest $500K–$2M+ in a purpose-built anechoic facility. Several practical alternatives exist: Sound Intensity Method (ISO 9614) Sound intensity measurements are inherently less sensitive to room reflections because intensity is a vector quantity — it distinguishes between outgoing sound (from the source) and incoming sound (reflections from room surfaces). This allows sound power determination in ordinary rooms without anechoic treatment. Trade-off: Requires specialised intensity probes and more complex measurement procedures. Acoustic Test Boxes For small products (electronics, components, transducers), a desktop-sized acoustic test box provides a controlled, low-noise environment that approximates anechoic conditions within a defined frequency range. These are significantly cheaper than a full chamber and can be placed directly on a production line. CRYSOUND offers a comprehensive range of acoustic test chambers designed for different testing scenarios: CRY723 Pneumatic Acoustic Test Chamber — A compact, shell-type test box ideal for smartphones and wireless wearables. Combine two CRY723 units with a CRY6151B analyzer for complete audio, ENC, and ANC measurements. CRY725 Pneumatic Acoustic Test Chamber — Designed for larger wireless devices such as laptops and walkie-talkies. Compatible with comprehensive testers and vector network analyzers. CRY7865 Pneumatic Acoustic Test Chamber — A high-performance drawer-style chamber with both acoustic isolation and RF shielding, ideal for production line audio and noise measurements of wireless electronic devices. CRY7412 Ultra-Quiet Chamber — An ultra-quiet chamber for testing very quiet sounds in noisy environments. Features a unique double-shell design for superior noise isolation. All models support pneumatic operation for fast, repeatable DUT loading on production lines — a practical alternative when a full anechoic chamber is not justified by the application. Portable Acoustic Arrays Modern acoustic imaging cameras can identify and localise noise sources in situ — in the factory, on the production line, or in the field — without any anechoic treatment. While not a substitute for standards-compliant sound power measurements, acoustic imaging enables rapid noise source diagnosis that previously required dedicated chamber time. The CRY8500 Series SonoCam Pi Acoustic Camera, is a portable acoustic imaging camera that delivers real-time sound source visualisation — ideal for R&D engineers working on noise source identification in automotive NVH, industrial equipment, and consumer electronics. In-Situ Sound Power (ISO 3744 with Corrections) ISO 3744 allows environmental correction factors to account for room reflections. If the correction is small (typically less than 2 dB), the measurement can be performed in a reasonably quiet industrial space without a purpose-built chamber. The SonoDAQ Pro data acquisition system combined with OpenTest software supports automated sound power calculations with environmental corrections built in — enabling standards-compliant measurements without a dedicated anechoic chamber. Frequently Asked Questions How much does an anechoic chamber cost? Costs vary widely based on size, performance requirements, and cut-off frequency. A small hemi-anechoic room for component testing may start around $100K–$300K, while a large automotive-grade full anechoic chamber can exceed $2M. For smaller products, acoustic test boxes offer similar isolation at a fraction of the cost. What is the difference between an anechoic chamber and a soundproof room? A soundproof room blocks external noise from entering but does nothing about internal reflections. An anechoic chamber both blocks external noise and absorbs internal reflections, creating a free-field environment for precision measurement. Can I do acoustic testing without an anechoic chamber? Yes. Depending on your application, alternatives include acoustic test boxes for small products, sound intensity methods (ISO 9614), portable acoustic imaging cameras like the CRY8500 SonoCam Pi, and in-situ measurements with environmental corrections using systems like SonoDAQ Pro. What frequency range does an anechoic chamber cover? The usable frequency range depends on the wedge depth and chamber dimensions. Most chambers are effective from their cut-off frequency (typically 80–200 Hz) up to 20 kHz or beyond. Below the cut-off, the chamber no longer provides adequate absorption. How is an anechoic chamber qualified? Chamber qualification follows ISO 26101, which verifies that the inverse-square law (sound pressure decreasing by 6 dB per doubling of distance) holds within specified tolerances at the measurement positions. Conclusion Anechoic chambers remain the gold standard for precision acoustic measurement — but they are not the only option. Understanding what your application truly requires helps you choose the right solution, whether that is a full anechoic room, a compact acoustic test chamber, or an in-situ measurement approach. At CRYSOUND, we provide the full spectrum: from purpose-built anechoic chambers to portable acoustic test boxes and advanced measurement systems — so you can get accurate results regardless of your facility constraints. Contact us to discuss which solution fits your testing requirements.

In many practical applications, data acquisition is not performed in an “ideal laboratory” environment. The device under test may be connected to mains power, distribution cabinets, frequency converters, or large electromechanical systems, while the acquisition card on the other side is connected via USB or Ethernet to a computer—sometimes operated directly by a person. These two sides are often not at the same electrical potential. If there is no effective electrical isolation inside the data acquisition card, this potential difference may propagate through signal lines, shields, or ground paths to the system side, leading to measurement distortion, interface malfunction, or even safety hazards. This is the fundamental reason why isolation exists in data acquisition systems. What Is the Isolation Rating of a Data Acquisition Card? In a data acquisition system, the isolation rating is not a simple voltage number, nor is it equivalent to “the voltage that the input can directly withstand.” It describes whether there is a reliable electrical isolation barrier between the measurement side (connected to sensors and the device under test) and the system side (connected to the host computer, communication interfaces, and power supply), and under what level of voltage stress this isolation remains valid. Isolation principle You can think of isolation as a bridge between two islands: The bridge allows information to pass—measurement data, digital communication, control signals. But it blocks dangerous currents—fault currents, ground-loop currents, and energy that could carry high potential to the host side. For this reason, isolation in data acquisition systems typically addresses both safety and measurement stability at the same time. Why Is Isolation Often More Important Than Accuracy Specifications? In many field applications, engineers do not encounter problems such as “insufficient resolution,” but instead: The same system works well in the lab, but noise increases dramatically on site. Once multiple devices are connected together, the data begins to drift. Replacing the computer or using a different power outlet suddenly makes the problem disappear. The common root cause behind these phenomena is often not algorithms or ADC performance, but rather improper handling of electrical potential relationships within the acquisition system. The value of isolation lies precisely here: by breaking unnecessary current loops and limiting the propagation paths of common-mode voltage and fault energy, isolation allows the acquisition system to behave in a controlled and predictable manner even in complex electrical environments. In industry discussions, the core values of isolation usually fall into three categories: signal integrity, safety, and instrument protection. Signal Integrity: Breaking Ground Loops and Improving Common-Mode Rejection Many cases of “inaccurate measurement” are not caused by ADC resolution, but by unwanted currents flowing through ground wires or shields. When the device under test and the host computer, enclosure, or other equipment are at different ground potentials, connecting them via signal cables may form ground loops. Power-line interference and electromagnetic noise then appear as “baseline noise” or ripple in the waveform. Isolation improves this by breaking the current loop paths. Safety: Confine High Potential and Fault Energy to the Measurement Side When measurement points are located near mains power, distribution cabinets, or frequency converters, the real risk is not merely “high voltage,” but where abnormal voltage or fault energy may propagate. If there is no clear electrical isolation between the measurement side and the host side, this energy may travel through signal or ground connections into the computer or communication interfaces, causing equipment damage or safety hazards. Isolation establishes a clear internal safety boundary: high potential and uncertain electrical environments are confined to the measurement side, while the system side—where the host computer and operator reside—remains within a controlled and safe potential range. If an abnormal condition occurs, the problem is contained on the measurement side and does not propagate further. Instrument Protection: A Larger Measurable Window Under High Common-Mode Voltage A non-isolated acquisition system effectively binds the measurement reference ground to system ground or earth. As a result, the measurable input range is centered around earth potential. If the entire signal shifts to a high common-mode potential, the front-end amplifier or ADC may exceed its allowable range or even be damaged. An isolated system allows the measurement reference to “float,” enabling the input measurement window to be centered around the isolated local ground. This permits operation under much higher common-mode voltages, with the ultimate limits determined by the isolation barrier and input protection circuitry together. Commonly Confused Isolation-Related Terms Isolation is often misunderstood because a single term—“isolation voltage”—is used to answer very different questions. The following clarifies these related but distinct concepts. Common-Mode Voltage Common-mode voltage refers to the voltage that is simultaneously applied to both measurement inputs relative to the acquisition system reference ground. It is not the signal of interest. The measurement signal concerns the difference between two input terminals, whereas common-mode voltage describes how high the two terminals are elevated together relative to ground. For example, in battery stacks or floating power systems, the signal itself may be only a few volts, but the entire source may be elevated tens or hundreds of volts above the acquisition card ground. In industrial environments, ground noise or electromagnetic interference may also impose time-varying AC voltage on both measurement leads. These “collectively elevated or oscillating voltages” constitute common-mode voltage. Working Voltage Working voltage is the voltage that can be continuously applied to a device over long periods. It is typically understood as the combination of measured voltage and common-mode voltage, and represents the condition under which the device can operate reliably over time. Withstand Voltage Withstand voltage refers to whether the isolation barrier can survive a very high voltage applied for a short duration without breakdown or damage. To verify this, a dielectric withstand (hipot) test is typically performed. During such a test, a voltage significantly higher than normal operating conditions is applied across the isolation barrier for approximately one minute. If no breakdown, abnormal leakage, or functional damage occurs, the isolation barrier is considered electrically robust. It is critical to note that withstand voltage does not indicate that the device can operate continuously at that voltage. It is a safety and quality verification metric, demonstrating that the insulation will not fail immediately under abnormal or extreme conditions. Input Overvoltage Protection Input overvoltage protection specifies the maximum allowable differential voltage between the positive and negative terminals of the same input channel. Exceeding this limit may damage the input circuitry. This is fundamentally different from isolation withstand voltage: Isolation withstand voltage applies between the measurement side and the system side. Overvoltage protection applies between the positive and negative terminals of the same channel. Measurement Category (CAT) Measurement category defines the severity of transient overvoltage that a measurement system may encounter in its electrical environment. Categories increase from CAT I to CAT IV: CAT I: Low-energy electronic circuits. CAT II: Household appliances and receptacle outlets, typically protected by indoor distribution panels. CAT III: Industrial distribution cabinets and environments with large motors, pumps, or compressors, subject to switching transients and inductive load surges. CAT IV: Outdoor power distribution points exposed to surges and lightning strikes. Pollution Degree Pollution degree describes environmental factors such as dust, moisture, and condensation that affect insulation surfaces. Higher pollution degrees reduce effective insulation performance, requiring higher baseline insulation strength. What Does "1000 V Isolation" Actually Mean? When a specification states “1000 V isolation,” three immediate questions must be asked, otherwise the number has no real comparability: Is it AC or DC? Is it Vrms, Vpk, or Vdc? Is it withstand voltage (short-term) or working voltage (long-term)? What exactly is isolated? Channel-to-ground? Channel-to-channel? Measurement side to USB/host side? The most important takeaway is this: “1000 V isolation withstand” does not automatically mean the system can continuously operate at 1000 V common-mode voltage, nor does it mean that 1000 V can be directly applied to the input. Continuous capability depends on working voltage, measurement category, input overvoltage protection, and the entire system chain including sensors, cables, and terminals. How Isolation Is Implemented: Isolation Barriers and Signal Transfer Methods Isolation is not simply “air separation,” but a combination of structure, materials, and signal-coupling mechanisms. Common isolation signal-transfer methods include: Inductive / Transformer-Based Isolation Inductive isolation transmits energy or information via magnetic fields rather than direct electrical conduction, fundamentally based on Faraday’s law of electromagnetic induction. Inductive isolation chip block Inside the chip, planar coils are fabricated on silicon or within the package, forming transformer-like structures. Transmitter side: current → coil → alternating magnetic field Receiver side: magnetic field variation → induced voltage → signal recovery Advantages include very high common-mode transient immunity (CMTI), high speed, low jitter, long-term stability, and excellent channel consistency. Disadvantages include higher power consumption and cost compared with capacitive isolation. Capacitive Coupling Capacitive isolation uses the “DC-blocking, AC-passing” property of capacitors to achieve voltage isolation, relying on electric-field variation within the dielectric. Capacitive isolation chip block Signal variation → electric-field variation → displacement current coupling Advantages include low power consumption, small die area, high integration, lower cost, and high speed. Disadvantages include higher sensitivity to common-mode dv/dt, stricter PCB symmetry requirements, and higher dependence on reference-ground layout. Optical Isolation Optical isolation uses light as the isolation medium, with air or transparent insulation providing physical separation. The principle is photoelectric conversion plus spatial isolation. Optical isolation chip block Electrical signal → LED emission → photosensitive device → electrical signal Advantages include simple structure, extremely high withstand voltage, good performance for low-frequency and switching signals, and strong EMC characteristics. Disadvantages include slower speed due to device latency, higher variability, and unsuitability for high-precision synchronous systems. Comparison of Isolation Technologies ItemInductiveCapacitiveOpticalWithstand voltage★★★★☆★★★☆★★★★★Transmission speed★★★★☆★★★★★★★Common-mode immunity★★★★★★★★☆★★EMI immunity★★★☆★★★★★★★★★Stability★★★★★★★★★★★Low power★★★★★★★★★★Suitable for DAQRecommendedRecommendedNot recommended A frequently overlooked but critical metric here is CMTI. In high dv/dt environments such as inverters, SiC/GaN power supplies, and motor drives, the issue is often not how high the static common-mode voltage is, but how fast it changes. Rapid high-voltage transients may couple through parasitic capacitances across the isolation barrier, disrupting or corrupting data transmission. Therefore, isolation must withstand not only voltage magnitude, but also voltage transition speed. Common Isolation Topologies in Data Acquisition Before asking whether a DAQ card is isolated, a more important question should be asked: where is the isolation applied? Different products may use entirely different isolation domains, resulting in very different capability boundaries and application suitability. Common DAQ isolation topologies include: Channel-to-system-ground isolation Bank (group) isolation Channel-to-channel isolation Channel-to-System-Ground Isolation Definition: Each channel (or group of analog front ends) is isolated from system ground and host ground, while channels typically share a common reference ground. Channel-to-system-ground This topology can: Break ground loops between the measurement side and the host side. Prevent high potential or fault energy from reaching the computer, USB, or network interface. Significantly improve stability when measurement and host grounds differ. The entire DAQ effectively “floats” with the device under test, while the host remains on the safe side. Suitable scenarios include industrial field measurements where all channels share the same potential. Bank Isolation Definition: Channels are divided into groups (banks). Each bank has its own isolation domain, with isolation between banks and between each bank and system ground. Bank isolation This topology allows multiple independent systems to be measured simultaneously while preserving multi-channel synchronization within each bank, balancing cost, size, and isolation capability. Channel-to-Channel Isolation Definition: Each channel has a fully independent isolation domain and reference ground. Channel-to-channel isolation Each channel effectively functions as an independent isolated acquisition system, suitable for battery stacks, distributed measurements, and scenarios with large inter-channel potential differences, at the expense of higher cost, size, and system complexity. Isolation Selection: From Parameters to Practical Judgment After understanding isolation concepts, topologies, and voltage ratings, the key question becomes: does a given isolation design truly fit the application? Many misjudgments arise from focusing on a single number such as “1000 V isolation” without clarifying where isolation is applied, for how long, and what additional protections are required. What Is Being Isolated, and Where Does the Isolation Occur? If all measurement objects belong to the same system and there is no potential difference between them, a Channel-to-System Ground Isolation data acquisition card should be selected. If the measurement objects belong to multiple different systems, but the measurement points within each system share the same ground reference, a Bank Isolation (group isolation) architecture should be selected. In this case, measurement points from different systems must not be connected to the same bank of the acquisition card. If all measurement objects belong to the same system but there are significant potential differences between them, a Channel-to-Channel Isolation data acquisition card should be selected. This is the prerequisite for evaluating all isolation-related parameters.If the isolation location is unclear, other voltage specifications are almost meaningless for comparison. Isolation Withstand Voltage of a Data Acquisition System At a minimum, the following information must be clearly specified:whether the voltage is AC or DC, the duration (typically a 1-minute withstand test), and only then the voltage value itself. If a data acquisition card specifies an AC isolation voltage of 1000 V, it means that an AC voltage with a peak value of ±1414 V is applied between the circuit grounds on both sides of the isolation barrier, and after 1 minute the leakage current remains below 0.1 mA. If a data acquisition card specifies a DC isolation voltage of 1000 V, it means that a +1000 V or −1000 V DC voltage is applied between the circuit grounds on both sides of the isolation barrier, and after 1 minute the leakage current remains below 0.1 mA.However, one must not assume that ±1000 V AC can be applied in this case—the two are not equivalent, because different devices have different withstand capabilities for AC and DC voltages. It should be emphasized that the withstand voltages discussed above are short-term withstand ratings. They do not mean that the device can operate continuously at a 1000 V common-mode voltage. They only indicate that the device will not be damaged under those conditions, not that normal operation is guaranteed. Maximum Common-Mode Operating Voltage This is the parameter that deserves particular attention when selecting a data acquisition card. In most cases, it refers to the long-term voltage difference between the measurement side and the system ground. For example, if we want to measure the current on a 220 V mains line, the corresponding common-mode voltage is: 220 V × 1.414 = 311 V Allowing at least a 50% margin, the data acquisition card should therefore support a maximum common-mode operating voltage greater than 466 V. If a specification sheet only provides isolation withstand voltage but does not clearly specify working voltage or maximum common-mode range, extreme caution is required in practical use. Input Voltage Range The input voltage range is also referred to as differential voltage. It defines how much voltage difference the input terminals of a channel can tolerate. The key question is what happens when this limit is exceeded:is the signal clipped, is the input shut down, or is permanent damage caused? This parameter determines whether the device can protect itself under wiring errors or abnormal conditions, or whether it will fail catastrophically. If the distinction between common-mode voltage and differential voltage is still unclear at this point, the following analogy may help. Measuring Across a River In the diagram, the person cannot approach the apple directly because of the river acting as an isolation barrier, so a caliper with an extended handle is used to measure the apple on the opposite bank. The 300 cm distance across the river corresponds to the common-mode voltage in the system, while the measurement range of the caliper (20 cm) corresponds to the differential voltage range. Isolation Structure of the SonoDAQ Module (Bank Isolation Example) After distinguishing between channel-to-ground isolation, bank isolation, and channel-to-channel isolation, as well as various isolation parameters, the next question for a specific product is: where exactly is the isolation boundary drawn? The following figure shows the isolation structure of a SonoDAQ module, illustrating the division of its isolation domains. SonoDAQ Module Isolation From the module structure, it can be clearly seen that SonoDAQ Pro adopts a bank isolation architecture (see Section 6.2). Each module is isolated from the host, while the four channels on each module are not isolated from each other. The module divides functionality and electrical domains into three parts: Measurement Side: Located on the left side of the module, directly connected to sensors and the device under test. This belongs to the measurement-side electrical domain and may be at a high or uncertain common-mode potential. Bank Isolation Domain: Located in the middle of the module, this is the primary isolation barrier between the measurement side and the system side. Multiple channels within the same bank share a common measurement-side reference ground and are collectively isolated from the system side through this isolation domain. As shown in the diagram, two types of isolation circuits are used: capacitive isolation for digital communication and magnetic (transformer-based) isolation for power. System Side: Located on the right side of the module, communicating with the host through the backplane. This side operates under system ground reference and connects to processors, communication interfaces, and the host computer. From Concept to Verification: Isolation Must Be Proven, Not Assumed Through the previous discussion, we have distinguished between differential and common-mode voltages and understood the respective roles of isolation withstand voltage, working voltage, and common-mode capability. While these concepts are not complex in specifications or standards, a more critical question remains in real engineering practice: Do these isolation boundaries actually hold under real-world conditions as the parameters suggest? For example, when the device under test operates at a high common-mode potential, the acquisition system must run online for extended periods, and the host computer and operators must always remain on the safe side. Simply “trusting a specification value” is far from sufficient. Rather than staying at the conceptual level, it is better to return to engineering practice. The following two experiments are not intended to demonstrate extreme parameter limits, but to address a more practical question. For this purpose, SonoDAQ Pro was selected as the test platform—not because of exceptionally high specifications, but because its isolation structure is clear and its boundaries are well defined, making it suitable for engineering-level isolation verification. The experiments are conducted from two perspectives: withstand voltage testing (hipot) and mains-powered incandescent lamp current measurement. Withstand Voltage Test (Hipot) Test objective: To verify that the isolation barrier can withstand high voltage under specified conditions without breakdown, providing an intuitive engineering verification result The general industry definition of dielectric withstand testing is to apply an elevated voltage across an insulation barrier for approximately 1 minute. Passing the test indicates that the insulation system has sufficient electrical strength under those conditions, while also clarifying the purpose and limitations of the test to avoid misinterpretation. Test equipment: WB2671 hipot tester Test conditions: 1000 V DC, duration 1 minute, leakage current threshold 0.1 mA Withstand Voltage Test Test Results 1.02 kV DC, duration 1 minute, leakage current = 0.03 mA, with no breakdown, flashover, or arcing observed. Explanation: SonoDAQ Pro adopts a bank isolation architecture, where the six slots are isolated from each other. Therefore, during testing, the hipot voltage was applied between Channel 1 of two adjacent modules. 220 V Mains Incandescent Lamp Current Measurement Experiment Test objective: To demonstrate how the data acquisition card can measure signals in a high-voltage system under real mains conditions, and to verify measurement correctness. Why an incandescent lamp? Its steady-state behavior closely resembles a resistive load, making current waveforms intuitive and easy to interpret. The cold filament has low resistance, producing a clear inrush current at power-on, which is suitable for demonstrating transient capture and trigger recording capability. 220 V Mains Incandescent Lamp Current Measurement Wiring In the diagram, the left side is the high-voltage area directly connected to the 220 V AC source. After all wiring is completed, the power plug is inserted. The right side contains the isolated data acquisition card, forming the low-voltage area. The computer and operator remain entirely on the safe side. The experiment used SonoDAQ Pro hardware with OpenTest software. The incandescent lamp was rated at 220 V / 60 W. The following photos show the setup before power-on (left) and after power-on (right). 220 V Mains Incandescent Lamp Current Measurement Test configuration: sampling rate 192 kSa/s, AC coupling for the input signal. The acquisition card directly measured the voltage across a 1.4 Ω shunt resistor. Using the “Record” function in OpenTest, the entire power-on and power-off process was recorded. Steady-State Current Waveform Steady-state current:Vrms = 386 mV → Irms = 386 / 1.4 = 275.7 mAFrequency f = 49.962 Hz Startup Transient Current Startup current:Vpeak = 2.868 V → Ipeak = 2.868 / 1.4 = 2.05 A Crest factor calculation:CF = Ipeak / Irms = 2.05 / 0.2757 = 7.44 Incandescent lamp power calculation:P = 220 V × 0.2757 A = 60.65 W Conclusion SonoDAQ Pro can accurately measure the operating current of an incandescent lamp connected directly to the mains without using a current transformer. This experiment does not merely verify whether mains signals can be measured; it verifies whether isolation can simultaneously ensure system safety and measurement accuracy when the device under test operates at a high common-mode potential over extended periods. Isolation Is Not a Parameter, but a Boundary Isolation is not “a single voltage value,” but rather defines where risk is confined and whether signals can still pass reliably. A reliable isolation solution is the result of structure, parameters, topology, and application scenario all being valid at the same time. To see more imformation about the SonoDAQ, please fill in the form below, and we will recommend the best solution to address your needs.

Sound is everywhere in our daily life: birdsong, street noise, engine roar, even the faint airflow from an air conditioner. For people, sound is not only about whether we can hear it, but whether it feels comfortable, is disturbing, or poses a risk. The same 70 dB can feel completely different; and when something feels "noisy", the cause may come from the source itself, the propagation direction, or reflections from the environment. When we turn this "perception" into quantifiable engineering data, the three most easily confused concepts are sound pressure, sound intensity, and sound power. They answer: Sound pressure: how loud it is at a specific point; Sound intensity: how much sound energy is propagating in a particular direction; Sound power: how loud the source is in terms of its total acoustic emission; This article explains sound pressure, sound intensity, and sound power in an intuitive way, so you can better understand sound. Sound Waves In engineering acoustics, sound pressure, sound intensity, and sound power are three fundamental and important physical quantities. Before introducing them in detail, we need the concept of a sound wave. A vibrating source sets the surrounding air particles into vibration. The particles move away from their equilibrium position, drive adjacent particles, and those adjacent particles generate a restoring force that pushes the particles back toward equilibrium. This near-to-far propagation of particle motion through the medium is what we call a sound wave. Figure 1. Propagation of a Sound Wave in Air Sound Pressure When there is no sound wave in space, the atmospheric pressure is the static pressure p0. When a sound wave is present, a pressure fluctuation is superimposed on p0, producing a pressure fluctuation p1. Here p1 is the sound pressure (unit: Pa). Therefore, sound pressure is the instantaneous deviation of the air static pressure caused by the sound wave. The human brain does not respond to the instantaneous amplitude of sound pressure, but it does respond to the root-mean-square (RMS) value of a time-varying pressure. Therefore, the sound pressure p can be expressed as: In practical engineering applications, the sound pressure level Lp: where Pref = 2 × 10-5 Pa is the reference sound pressure. In practice, we usually use sound pressure level (dB) to characterize sound pressure, rather than using pressure in pascals. Why? Figure 2 answers this well. From a library to the entrance of a high-speed rail station, sound pressure may increase by a factor of 100, while sound pressure level increases by only 40 dB. This reflects the difference between a linear scale and a logarithmic scale. From an engineering perspective, using sound pressure directly leads to large numeric variations that are inconvenient for evaluation. Moreover, the human auditory system is closer to a logarithmic response, so sound pressure level better matches hearing. Figure 2. Sound Pressure and Sound Pressure Level Sound Intensity Sound intensity describes the transfer of acoustic energy. It is the acoustic power passing through a unit area per unit time. It is a vector quantity that is directional, with units of W/m2, defined as the time average of the product of sound pressure and particle velocity: where v(t) denotes the particle velocity vector. Under the ideal plane progressive-wave approximation, sound pressure and particle velocity approximately satisfy: where ρ is the air density, c is the speed of sound. Therefore, the magnitude of sound intensity along the propagation direction can be written as: Similarly, sound intensity has a corresponding intensity level LI: where I0 = 10-12 W/m2 is the reference sound intensity. Compared with sound pressure level measurements, sound intensity measurements have the following characteristics: Directional:it can distinguish whether acoustic energy is propagating outward or flowing back, so under typical field conditions it is often less sensitive to reflections and background noise; Source localization:intensity scanning can directly reveal the main radiation regions and leakage points, making remediation more targeted; Higher system complexity:it typically requires an intensity probe, with higher overall cost and more setup and calibration effort; Figure 3. Sound Intensity Testing A key advantage of sound intensity measurement in engineering applications is that it characterizes both the direction and magnitude of acoustic energy flow. It can separate the contributions of outward radiation from the source and reflected backflow from the environment, so under non-ideal field conditions it tends to be less affected by reflections and background noise. In addition, the sound intensity method can obtain sound power directly by spatially integrating the normal component of intensity over an enclosing surface. Combined with surface scanning, it can identify dominant source regions and locate leakage points. Therefore, it is highly practical and interpretable for noise diagnosis, verification of noise-control measures, and sound power evaluation. The key instrument for sound intensity testing is the sound intensity probe. Unlike a single microphone, an intensity probe is not used merely to measure “how large the pressure is”; it must provide the basic quantities required for calculating intensity (sound pressure and particle velocity). Therefore, the probe typically outputs two synchronous channels and, together with a two-channel data-acquisition front end and dedicated algorithms, yields intensity results. In engineering practice, the probe often includes interchangeable spacers, positioning fixtures, and windshields. Channel amplitude/phase matching, phase calibration capability, and airflow-interference mitigation directly determine the credibility and usable frequency range of intensity measurements. Two types of sound intensity probes are commonly used: P-U probes (pressure-particle-velocity) and P-P probes (pressure-pressure). A P-U probe consists of a microphone and a velocity sensor, measuring sound pressure p(t) and particle velocity v(t) simultaneously. The principle is more direct, but particle-velocity sensors are often more sensitive to airflow, contamination, and environmental conditions, requiring more protection and maintenance in the field and usually costing more. Figure 4. P-U Sound Intensity Probe (Microflown) A P-P probe uses two matched microphones aligned on the same axis. It uses the two pressure signals p1(t) and p2(t) to estimate the particle-velocity component v(t). However, it is sensitive to inter-channel phase matching and the choice of microphone spacing - the spacing determines the effective frequency range: a larger spacing benefits low frequencies, but high frequencies suffer from spatial sampling error; a smaller spacing benefits high frequencies, but low frequencies become more susceptible to phase mismatch and noise. Figure 5. P-P Sound Intensity Probe (GRAS) P-U probes are relatively niche, mainly because it is difficult to make them both stable and inexpensive, and they generally have poorer resistance to airflow. P-P probes, thanks to their good field robustness and the ability to adjust bandwidth flexibly via microphone spacing, are currently the mainstream choice in engineering applications. Sound Power Sound power W is the rate at which a source radiates acoustic energy, with units of watts (W). For any closed measurement surface S enclosing the source, the sound power equals the integral of the normal component of sound intensity over that surface: where n is the unit normal vector pointing outward from the measurement surface. Sound power level Lw is defined as: where W0 = 10-12 W is the reference sound power. Figure 6. Sound Power Measurement Sound power characterizes a source's inherent acoustic emission capability: the total acoustic energy it radiates per unit time. It has little to do with measurement distance or microphone position, and ideally does not depend on how "loud" it is at a particular point in a room. This is fundamentally different from sound pressure and sound intensity. To better understand sound pressure, sound intensity, and sound power, you can imagine noise as water flow. Sound pressure is like the "water pressure" you feel when you put your hand at a certain location (it changes with distance to the nozzle, direction, and the shape of the basin). Sound intensity is like the instantaneous "direction and rate of flow" (it has direction and can even be reflected by walls, creating backflow). Sound power is like "how much water the nozzle sprays per second" - it is a property of the nozzle itself. In measurement, it is obtained by integrating the outward normal flow over a surface surrounding the device. Figure 7. Analogy of Sound Pressure, Sound Intensity, and Sound Power In real projects, the algorithms for sound pressure, sound intensity, and sound power are relatively mature. The hardest part is acquiring the signals accurately and obtaining results quickly. In particular, tasks such as multi-channel microphone arrays, sound intensity, and sound power impose three hard requirements on the data-acquisition front end: low noise and wide dynamic range, strict synchronization and phase consistency, and stable on-site connections and power. SonoDAQ + OpenTest is positioned to provide a "front-end acquisition + synchronous analysis" foundation for engineering acoustics, allowing engineers to focus more on operating-condition control and data interpretation. It delivers the most value in the following types of projects: Sound intensity diagnostics: dual-channel synchronous sampling plus better amplitude/phase consistency management provide a more stable data basis for P-P intensity probes and intensity scanning. Microphone array systems: better aligned with engineering deployment needs in channel scalability, synchronization, and cabling, making it suitable for building expandable distributed test platforms. Sound power and standardized testing: helps engineers quickly lay out measurement points, covering multiple international sound power test standards. With guided configuration, one-click testing, and automatic report export, it saves substantial time and effort for engineers. Figure 8. SonoDAQ + OpenTest To see more clearly how SonoDAQ is connected and configured, typical application cases (such as equipment noise evaluation, sound source localization, and sound power testing), and commonly used BOM lists, please fill in the form below, and we will recommend the best solution to address your needs.