This article introduces how to build a multi-channel sound level meter compliant with IEC 61672-1 using OpenTest, in combination with SonoDAQ data acquisition hardware and measurement-grade microphones. The system supports A / C / Z frequency weighting, F / S / I time weighting, and standard acoustic quantities such as Lp, Leq, and Ln, making it suitable for a wide range of applications including environmental noise, product noise, and automotive NVH testing. From Handheld Sound Level Meters to Multi-Channel Sound Level Measurement Platforms In acoustics and vibration testing, one fundamental question appears in almost every project: “How loud is it?” From office equipment and household appliances to automotive NVH and industrial machinery, regulations, standards, and internal quality criteria all rely on quantitative evaluation of Sound Pressure Level (SPL). Traditionally, this is done using a handheld sound level meter compliant with IEC 61672, placed at a specified position to read an A-weighted sound level for compliance checks and quality verification. IEC 61672 defines detailed requirements for sound level meters in terms of frequency weighting, time weighting, linearity, self-noise, and dynamic range, and classifies instruments into Class 1 and Class 2, with Class 1 having stricter requirements and being suitable for laboratory and type-approval testing. As product structures and test requirements evolve, engineers increasingly expect more than what a single handheld meter can offer: Measure multiple positions simultaneously to compare different locations or operating points Combine sound level data with spectra and octave-band analysis to quickly identify problematic frequency regions Synchronize sound level measurement with speed, vibration, temperature, and other physical quantities for NVH diagnostics Integrate sound level measurement into automated and batch test workflows, rather than relying on manual spot checks This leads to the demand for multi-channel sound level meters: systems that not only meet IEC 61672-1 Class 1 accuracy requirements, but also provide multi-channel capability, scalability, and automation. OpenTest, developed by CRYSOUND, is a new-generation acoustic and vibration test platform. Its dedicated Sound Level Measurement module, combined with CRY5820 SonoDAQ Pro front-end hardware and measurement microphones, enables multi-channel sound level measurements consistent with Class 1 sound level meters. Figure 1. From handheld sound level meters to multi-channel sound level measurement platforms IEC 61672: What Are We Actually Measuring? Meaning of Sound Pressure Level (Lp) Sound Pressure Level (SPL) is a logarithmic measure of the root-mean-square sound pressure prms​ relative to the reference pressure p0​, which is 20 μPa in air, defined as: When prms​=1 Pa, the SPL is approximately 94 dB, which is why 94 dB / 1 kHz is commonly used as the reference level for acoustic calibrators. Frequency Weighting: A / C / Z Human hearing sensitivity varies with frequency. IEC 61672 requires all sound level meters to support A-weighting, while Class 1 instruments must also support C-weighting. Z-weighting (Zero weighting, i.e. flat response) is optional. A-weighting (dB(A))Based on the 40-phon equal-loudness contour, with significant attenuation at low and very high frequencies. It is widely used in regulations and standards as an indicator correlated with perceived loudness. C-weighting (dB(C))Much flatter than A-weighting, with less low-frequency attenuation. It is suitable for evaluating peak levels, mechanical noise, and high-level events. Z-weighting (dB(Z))Essentially flat within the specified bandwidth, preserving the original spectral energy distribution, and useful for detailed analysis. While A-weighting dominates regulations, it is not a perfect psychoacoustic model. In cases involving strong low-frequency content, modulation, or tonal components, A-weighted levels may underestimate perceived annoyance.For design and diagnostic work, it is therefore recommended to combine C/Z weighting, octave-band spectra, and sound quality metrics. Time Weighting: Fast / Slow / Impulse IEC 61672 defines the following time weightings: F (Fast): time constant ≈ 125 ms, suitable for rapidly fluctuating sound levels S (Slow): time constant ≈ 1 s, suitable for observing overall trends I (Impulse): designed for impulsive signals, more sensitive to short-duration peaks Common sound level descriptors include: LAF / LAS / LAI: A-weighted sound levels with Fast / Slow / Impulse time weighting LCpeak: C-weighted peak sound level Energy-Based and Statistical Quantities: Leq, SEL, Ln IEC 61672 also defines commonly used acoustic quantities: Leq,T / LAeq,TEquivalent continuous sound level over a time period T, widely used in environmental and product noise evaluation. Sound exposure and sound exposure level: E, LE / LAE (SEL)Represent the total sound energy of an event, commonly used for aircraft, traffic, and single-event noise evaluation. Lmax / Lmin: Maximum and minimum sound levels under a specified time weighting Lpeak (typically LCpeak): Peak sound level based on peak sound pressure Statistical levels Ln (L10, L50, L90, etc.)Levels exceeded for n% of the measurement time, commonly used in environmental noise analysis. Band Levels: Octave and 1/3-Octave Bands Although octave-band filters are specified in IEC 61260, IEC 61672 aligns with them in terms of frequency response and standard center frequencies. Common analyses include: 1-octave band levels (e.g. 31.5 Hz–16 kHz) 1/3-octave band levels, offering finer frequency resolution for identifying narrow-band noise and structural resonances Together, these quantities define the full scope of sound level measurement—from instantaneous readings to time-averaged values, and from broadband levels to frequency-resolved analysis. Sound Level Measurement with OpenTest Setup: Building the Signal Chain from Source to Software Hardware Preparation Data acquisition front-endFor example, CRY5820 SonoDAQ Pro, a modular multi-channel data acquisition system supporting 4–24 channels per unit and scalable to thousands of channels. It features 32-bit ADCs, up to 170 dB dynamic range, 1000 V channel isolation, and ≤100 ns PTP/GPS synchronization accuracy, suitable for both laboratory and field acoustic and vibration testing. SensorsOne or more measurement-grade microphone sets (with preamplifiers), positioned at representative measurement or listening locations. Computer and softwareA PC with OpenTest installed and the Sound Level Measurement module licensed. Connecting Devices and Channels in OpenTest Launch OpenTest and create a new project. In Hardware Settings, click “+”; available devices (including those connected via openDAQ or ASIO) are automatically detected. Select the required acquisition devices (e.g. SonoDAQ) and add them to the project. In Channel Settings, add the microphone channels and configure sampling rate and input range. At this point, the signal chain Sound source → Microphone → DAQ → OpenTest is fully established. Calibration: Setting the Acoustic Reference To ensure absolute accuracy, each channel must be calibrated using a Class 1 acoustic calibrator. Open the Calibration dialog in OpenTest. Select the microphone channels to be calibrated. Mount the calibrator on the microphone and start calibration. Once the reading stabilizes, complete the calibration. OpenTest automatically updates the channel sensitivity so that the 94 dB SPL reference point is aligned. For comparison tests, a handheld sound level meter (e.g. CRY2851) can be calibrated using the same calibrator (e.g. CRY3018) to ensure both systems share the same acoustic reference. Measurement: Acquiring Sound Level Time Histories Switch to the Sound Level Meter module in OpenTest and select: Measurement channels Quantities to compute (Lp, Leq, Ln, etc.) Frequency weighting (A / C / Z, computed simultaneously) Typical operating conditions may include: Idle Typical load Full load For each condition: Stabilize the DUT at the target operating state. Start measurement in OpenTest. Monitor sound level time histories, octave-band plots, and FFT spectra in real time. Stop after sufficient duration and name the dataset accordingly. Each measurement is automatically saved as a dataset for later comparison and analysis. Figure 2. Multi-channel sound level measurement using OpenTest Reporting: From Data to Traceable Documentation After measurements, OpenTest’s reporting function can be used to generate structured reports: Project information, DUT details, operating conditions Selected acoustic quantities (Leq, Lmax, LCpeak, Ln, etc.) Company logo and test personnel information Raw waveforms and analysis results can also be exported for archiving or further processing. Figure 3. OpenTest sound level measurement report Comparison with CRY2851 Handheld Sound Level Meter CRY2851 is a Class 1 sound level meter compliant with IEC 61672-1:2013, supporting A/C/Z weighting, F/S/I time weighting, and a full set of acoustic parameters. Comparison procedure: Environment and operating conditionsLow-background laboratory or semi-anechoic room; multiple operating states. Calibration consistencyBoth systems calibrated with the same Class 1 calibrator (94 dB or 114 dB at 1 kHz). Sensor placement and acquisitionMicrophones positioned as closely as possible at the same measurement point. Result comparisonCompare LAeq, LAF, LCpeak, and other key parameters under identical weighting and time windows. Figure 4. CRY2851 vs. OpenTest multi-channel sound level measurement Typical Applications of the Sound Level Measurement Module Consumer Electronics / IT Equipment Evaluate the impact of cooling strategies on LAeq and LAFmax Combine sound level limits with sound power measurements Integrate FFT, 1/3-octave, and sound quality metrics Automotive NVH / Interior Acoustics Multi-position sound level measurement in the cabin Comparison across driving conditions Coupling with order analysis and sound quality modules Household Appliances and Industrial Machinery Supplement sound power tests with multi-point sound level monitoring Integrate into production lines using sequence mode Identify problematic frequency bands via 1/3-octave analysis Environmental and Long-Term Monitoring Multi-point statistical sound level evaluation (L10, L50, L90) Long-term data logging and remote access If you are already familiar with handheld sound level meters, the OpenTest Sound Level Measurement module effectively upgrades them into a system that is: Multi-channel Traceable (raw data + analysis + reports) Expandable, working seamlessly with sound power, sound quality, FFT, and octave-band analysis modules, and supporting automated test workflows. Welcome to fill in the form below ↓ to contact us and book a demo and trial of the OpenTest Sound Level Meter module. You can also visit the OpenTest website at www.opentest.com to learn more about its features and application cases.

In acoustic testing, acoustic metrology, and product noise evaluation, the term measurement microphone typically refers to a condenser measurement microphone. Its signal generation relies on a polarization electric field: sound pressure changes the capacitance, and the front-end circuitry converts this change into an electrical signal. Depending on how the polarization field is provided, measurement microphones generally fall into two categories: externally polarized (polarization high voltage supplied by the measurement system, typically 200 V) and prepolarized (an internal electret provides the equivalent polarization, so no external high voltage is needed). Both can deliver high-precision measurements; the key to selection is system compatibility, environmental constraints, and maintenance cost. This article first explains how prepolarized and externally polarized microphones work and differ. It then compares power/front-end compatibility, noise and dynamic range, environmental robustness, and long-term stability. Next, it gives selection tips by scenario (metrology, approval tests, field, multichannel). It ends with a quick decision checklist. System Requirements Externally Polarized An externally polarized microphone requires a dedicated polarization unit / microphone power supply (provides 200 V polarization) to provide a stable polarization voltage (commonly 200 V) and to match the preamplifier interface (often 7-pin LEMO).This signal chain is closer to traditional metrology setups and is commonly used in laboratories and traceable calibration scenarios. Figure 1. Externally Polarized Microphone Structure Diagram Figure 2. Externally Polarized Microphone Set Prepolarized A prepolarized microphone uses an internal electret to provide equivalent polarization, so no external polarization voltage is required.System integration is simpler, making it well-suited for field work, mobile testing, and multi-channel distributed deployments. IEPE interfaces are widely used and broadly compatible; many data acquisition devices provide built-in IEPE inputs, which can significantly reduce overall equipment cost. (IEPE is the international term; some companies also refer to it as CCP or ICP.) Figure 3. Prepolarized Microphone Structure Diagram Figure 4. Prepolarized Microphone Set Engineering Trade-offs From an engineering application perspective, the main differences are: System compatibility: Externally polarized microphones depend on 200 V polarization and specific front-end/interfaces; prepolarized microphones place fewer requirements on the front-end and enable more flexible integration. Environmental robustness: High humidity, condensation, dust, oil mist, and similar environments can amplify insulation and leakage issues; prepolarized microphones often achieve more stable results. For high-temperature applications, carefully verify the model’s temperature limit and long-term drift data; externally polarized microphones are more commonly used where high-temperature stability and metrology-grade requirements are prioritized. Deployment and maintenance: Prepolarized solutions avoid high-voltage risk, deploy faster, and typically cost less at scale. Externally polarized setups demand higher standards for cleanliness, insulation, connector reliability, and troubleshooting capability. Selection Guidelines Front-End and Power Architecture If your existing front-end natively supports 200 V polarization and you have long used that metrology signal chain, prioritize externally polarized microphones to minimize retrofit effort and compatibility risk. If your front-end does not support polarization high voltage, or your system is mainly based on constant-current powering (e.g., CCLD/IEPE), prioritize prepolarized microphones for higher deployment efficiency and broader compatibility. Environmental Constraints (Humidity / Contamination / Temperature) For high humidity, condensation, dust, or oil mist in the field: prioritize prepolarized microphones or models with protective designs, and pay close attention to connector and cable protection. For high temperature or thermal cycling: base the choice on datasheets and stability data. Both externally polarized and high-temperature prepolarized models may be suitable, but you must verify the temperature limit and drift specifications. Align the Key Performance Targets Low-noise measurement: focus on equivalent self-noise, front-end noise, cable length, and shielding/grounding strategy. High SPL / shock measurement: focus on maximum SPL, distortion, overload recovery, and front-end input headroom (capsule size selection is often more critical than polarization method). Consistency / traceability: focus on calibration system, long-term drift, temperature coefficient, and maintenance interval. Budget and Total Cost of Ownership If budget is tight, channel count is high, or you need rapid scaling: prioritize prepolarized microphones. Without external polarization high voltage, the measurement chain is simpler and total investment is usually lower. If an externally polarized chain is required: include the external polarization power supply/adapter as a mandatory budget item. In addition to the microphone and preamplifier, a stable 200 V polarization supply is required, and the polarization supply can be costly. For multi-channel deployments, total cost rises significantly with channel count. If the laboratory already has sufficient channels of external polarization supplies, the incremental cost can be much lower. Conclusion There is no absolute “better” option between prepolarized and externally polarized microphones. A more reliable engineering approach is to first define the measurement chain and environmental constraints, then finalize the model selection using key metrics such as noise, dynamic range, consistency, and traceability. 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.

This integrated single-station EoL test solution enables automotive HVAC air vent suppliers to perform NVH (noise/BSR), motor electrical testing, and vane presence detection in a single inspection step, helping to improve overall test efficiency and reduce labor dependency. System Block Diagram of the Automotive HVAC Air Vent Test Solution Modern automotive HVAC air vent assemblies increasingly integrate multiple drive motors, multi-row vanes (louvers), and smart features such as automatic airflow control and voice interaction. As a result, upstream process variation or assembly defects can translate directly into vehicle-level concerns—typically perceived as abnormal noise, buzz/squeak/rattle (BSR), airflow direction mismatch, or reduced airflow caused by missing/misassembled vanes. To reduce rework and prevent customer complaints, suppliers increasingly require 100% end-of-line (EoL) testing on the production line, covering NVH (noise/BSR), motor electrical testing, and vane presence detection. CRYSOUND Single-Station EoL Test Solution CRYSOUND’s automotive HVAC air vent EoL test solution enables customers to perform single-station, 100% testing of noise/BSR, motor electrical testing, and vane presence detection. The solution integrates CRYSOUND’s in-house hardware and software, CRY3203-S01 measurement microphone set, SonoDAQ, CRY7869 acoustic test box, and OpenTest. And it combines electroacoustic measurement with abnormal noise analysis (sound quality and AI-based algorithms) to identify noise/BSR issues that FFT and Leq may miss. It also integrates motor electrical testing and vane presence detection, enabling one-time clamping and a single OK/NG decision within the same sound-insulated EoL station. Schematic of the HVAC Air Vent Test Fixture Customer Results: Efficiency, Labor, and Quality Gains Replaced manual listening with machine-based detection, enabling unified criteria with quantitative, traceable results. One fixture, three test positions: supports parallel or mixed testing of left/center/right dashboard air vents, improving efficiency by >100%. Variant support via fixture changeover: reuse the same test station across different products, reducing repeated capital investment. One-operator, one-click inspection: a single line can save 1–2 long-term operators. EoL Test Equipment for Automotive HVAC Air Vent Typical Target Users This solution is designed for suppliers of motorized air vents and other motor-driven interior components，such as Valeo S.A.，Ningbo Joysonquin Automotive Systems Co., Ltd. and Jiangsu Xinquan Automotive Trim Co., Ltd. Main Hardware and Software Configuration ProductQty.NoteCRY3203-S01 Measurement Microphone Set1Measurement Microhone SetCRY5820 SonoDAQ Pro1Audio AnalyzerCRY7869 Acoustic Test Box1Test EnvironmentOpenTesthttp://www.opentest.com1SoftwareFixture1CustomizablePC & Monitor1(Optional) Feel free to fill in the form below ↓to contact us. Our team can share application-specific EoL testing recommendations based on your automotive HVAC air vent requirements.

In industrial production and environmental monitoring, excessive noise implies compliance risks or potential complaint disputes. To handle this, you need a professional sound level meter (SLM) that provides "credible, traceable, and analyzable data." Faced with price differences ranging from hundreds to tens of thousands of dollars, and a complex array of parameters, how do you choose without making costly mistakes? We have distilled the complex selection process into a "4-Step Decision Method" to help you quickly find the balance between your budget and your needs. Step 1: Define the "Purpose" — Does the data need to be externally accountable? This is the first watershed moment in selection, directly determining the equipment's "Accuracy Class." Scenario A: Data must be "Externally Accountable" Typical Use Cases: Environmental law enforcement, third-party testing, laboratory R&D, legal arbitration. Must Choose: Class 1 Sound Level Meter. Key Reason: The difference between Class 1 and Class 2 goes beyond reading errors. The core difference lies in the Frequency Response Range. Class 1 Devices (e.g., CRY2851): Typically cover a wide band of 10 Hz – 20 kHz, capturing extremely low-frequency vibrations and ultra-high-frequency noise, fully meeting strict standards like IEC 61672-1:2013 Class 1. Class 2 Devices: Usually have a narrower frequency range (e.g., 20 Hz – 8 kHz) with potential attenuation at high or low ends, making them unsuitable for strict metering or certification scenarios. Scenario B: Used only for "Internal Management" Typical Use Cases: Workshop inspections, equipment spot checks, community surveys, internal process comparisons. Recommended: Class 2 Sound Level Meter. Core Advantage: It meets the vast majority of industrial and environmental noise measurement needs and is the ideal choice for internal control. Step 2: Clarify "Indicators" — What exactly are you measuring?  Selecting the wrong indicators renders the data useless. Focus on the following two points: Frequency Weighting (A, C, Z): Which one to use? A-Weighting (Most Common): Simulates the human ear's response (insensitive to low frequencies). Must be used for Environmental Noise Evaluation and Occupational Health Assessments (e.g., 85 dB(A) limits). C-Weighting: Less attenuation at low frequencies, reflecting the total energy of the sound more truly. Often used for Mechanical Noise and Impact Sound where rich low-frequency components exist. Z-Weighting (Zero Weighting): Flat response across the entire frequency range with no attenuation. Must be used when you need Spectrum Analysis or deep research into noise components to preserve the original signal. "Instantaneous Value" or "Statistical Value"? For quick site checks: Focus on Lp (Instantaneous Sound Pressure Level) and Lmax (Maximum Sound Level). For scientific assessment or reporting: You must have Leq (Equivalent Continuous Sound Level). This is the core metric for evaluating noise energy over a period of time. Professional equipment (like CRY2850/2851) comes standard with integrating functions to automatically calculate Leq. Figure 1. Software Interface Diagram Step 3: Confirm if "Analysis" is needed — Do you need to find the noise source?  This distinguishes a "regular noise meter" from a "professional sound level meter." Looking at a total value (e.g., 85dB) only tells you "it's noisy here"; seeing the spectrum tells you "where is it noisy." When do you need Spectrum Analysis (1/1 Octave, 1/3 Octave, or FFT)? Noise Control: Determining if noise comes from a fan (aerodynamic noise) or a motor (electromagnetic noise). R&D: Comparing sound quality differences between competing products or iterations. Diagnostics: Distinguishing between high-frequency bearing squeal and low-frequency structural resonance. Selection Advice: Taking the CRY2851 as an example, it supports both OCT Analysis and FFT Analysis. If your goal is to "solve problems" rather than just "record numbers," be sure to choose a device with spectrum functions. Figure 2. Measurement Demonstration Step 4: Plan the Measurement "Mode" — Single measurement or long-term monitoring? Many projects fail because the device "measures accurately, but is hard to use." Dynamic Range: Say goodbye to "Manual Gear Shifting" Old equipment requires manual range switching, which is prone to errors. Modern sound level meters (like CRY2851) feature a >120 dB wide dynamic range, covering everything from whispers to roaring engines without switching gears—preventing errors and improving efficiency. Data Export: Ensure data is "Portable and Usable" Ensure the device supports automatic storage to an SD card or internal memory and exports in universal formats (like CSV). Avoid the trap of "measuring data but failing to record it manually." Remote Monitoring Capability (Essential for Outdoor/Long-term)  For long-term scenarios like construction sites or traffic monitoring, the device must have: Communication Functions: (LAN/Serial Port) for real-time remote data transmission. Outdoor Protection: (e.g., paired with NA41 Outdoor Kit, IP65 rating) to withstand rain and dust; otherwise, the equipment is easily damaged. Quick Selection Cheat Sheet To help you decide quickly, we have summarized three typical application scenarios based on the four-step method above: Figure 3. Handheld Measurement Operation The "Avoid Pitfalls" Checklist: Check these 5 points last Check the Standard: Confirm compliance with the latest IEC 61672-1:2013 standard. Check Bandwidth: Even for Class 2 meters, ensure the frequency range covers your main noise sources to avoid missed detections. Check Calibration: Buying a Class 1 SLM requires a Class 1 Sound Calibrator (e.g., CRY563A); otherwise, the system accuracy is downgraded. Check Range: Prefer "Wide Dynamic Range" or "Auto-Range" devices; refuse manual gear shifting. Check Accessories: Windscreens and protective cases are mandatory for outdoor use. Selecting a sound level meter is essentially balancing "Risk vs. Cost." If you still have doubts about "Class 1 vs. Class 2" or "Whether Spectrum Analysis is needed," CRYSOUND is ready to provide full lifecycle support: Pre-sales: Our application engineers provide one-on-one scenario consulting to help you match precisely and avoid wasting money. After-sales: We offer a full suite of services from calibration and training to long-term technical support, ensuring a complete chain of evidence. Instead of struggling with parameters alone, get in touch with our team using the form below to receive a configuration plan tailored to your application.