In acoustic measurements (SPL, frequency response, noise, reverberation, etc.), large errors often come not from instrument accuracy, but from a mismatch between the assumed sound field and the actual one. What a microphone reads as sound pressure is not strictly equivalent across different fields—especially at mid and high frequencies, where the microphone dimensions become comparable to the acoustic wavelength. Measurement microphones are commonly categorized by the field for which their calibration/compensation is defined: Free-field, Pressure-field, and Diffuse-field (Random incidence). This article uses engineering-oriented comparison tables and common-pitfall checklists to explain the differences among the three sound-field types, their typical application scenarios, and key usage considerations. It also provides selection rules that can be directly incorporated into test plans, helping to improve measurement repeatability and comparability. Build Intuition With One Picture The following diagrams illustrate the three typical sound-field assumptions used in microphone calibration and selection. Figure 1  Free field: reflections negligible, wave incident mainly from one direction Figure 2  Pressure field: coupler/cavity measurement focusing on diaphragm surface pressure Figure 3  Diffuse (random-incidence) field: energy arrives from many directions (statistical sense) Quick Comparison for Engineering Selection TypeField assumptionTypical scenariosPlacement / orientationMain error driversFree-field microphoneReflections negligible; primarily single-direction incidence (often 0°)Anechoic measurements; on-axis loudspeaker response; front-field SPLAim at source (0°)Angle deviation; unintended reflections; fixture scatteringPressure-field microphoneMeasure true pressure at diaphragm surface (often in small cavities)Couplers; ear simulators; boundary/flush measurementsFlush-mounted or connected to couplerLeaks; cavity resonances; coupling repeatabilityDiffuse-field (random-incidence) microphoneEnergy arrives from all directions with equal probability (statistical)Reverberation rooms; highly reflective enclosures; diffuse-field testsOrientation less critical, but mounting must be controlledNot truly diffuse in real rooms; local blockage/reflections Free Field: Estimate the Undisturbed Sound Pressure A free field is an environment where reflections are negligible and sound arrives mainly from a defined direction (commonly 0° to the microphone axis). Because the microphone body perturbs the field, a free-field microphone typically includes free-field compensation, so the indicated pressure better represents the pressure that would exist without the microphone in place. Typical Use Cases Anechoic or quasi-free-field SPL measurements On-axis loudspeaker frequency response and source characterization Tests with a strictly defined incidence direction Practical Notes Keep 0° incidence when specified; off-axis angles can cause significant high-frequency deviations. Minimize scattering from fixtures (stands, adaptors, fixture、cable、windscreens). Control nearby reflective surfaces that break the free-field assumption. Pressure Field: Measure Diaphragm Surface Pressure A pressure field is commonly associated with small enclosed volumes (couplers/cavities). Here, the quantity of interest is the true pressure at the diaphragm surface. The microphone often becomes part of the cavity boundary. Typical Use Cases Pistonphone/coupler calibration and cavity measurements IEC ear simulators and couplers for headphone and in-ear testing Flush/boundary pressure measurements Practical Notes Seal and coupling are critical; small leaks can strongly affect low and mid frequencies. Cavity resonances can shape high-frequency response; follow the applicable standard or method. Maintain consistent mounting force and assembly for repeatability. Diffuse Field: An Average Over Angles A diffuse field (random incidence) assumes that sound energy arrives from all directions with equal probability, in a statistical sense. This is approached in reverberation rooms or highly reflective enclosures. Diffuse-field microphones are designed so their response better matches the average over many incidence angles. Typical Use Cases Reverberation-room measurements and room acoustics Noise and SPL measurements in reflective cabins (vehicle or enclosure) Statistical measurements where multi-direction incidence dominates Practical Notes A normal room is not necessarily diffuse; strong direct sound breaks the assumption. Proper installation and operation remain essential: large fixtures, mounting brackets, and obstructions can alter the characteristics of the local acoustic field. Keep measurement locations consistent; position changes alter modal and reverberant contributions. Rule of Thumb: Write the Field Assumption into the Test Plan Quasi-anechoic, direction defined → choose a free-field microphone Coupler/cavity/boundary pressure → choose a pressure-field microphone Highly reflective, multi-direction incidence → choose a diffuse-field microphone When the field is uncertain, define the geometry first (direct-to-reverberant ratio, incidence direction, distance), then apply an appropriate calibration or correction strategy to control the dominant error sources. Common Pitfalls Using a free-field microphone in a coupler/cavity: high-frequency deviations are often exaggerated. Free-field testing without controlling angle: off-axis error grows at mid and high frequencies. Treating a normal room as diffuse: if direct sound dominates, the diffuse-field assumption fails. Conclusion Free field, pressure field, and diffuse field are not marketing terms—they tie microphone design and calibration assumptions to specific acoustic models. By explicitly documenting the assumed field (geometry, angle, reflections, calibration and corrections) in your test plan, you can significantly improve repeatability and comparability across measurements. To learn more about microphone functions and measurement hardware solutions, visit our website—and if you’d like to talk to the CRYSOUND team, please fill out the “Get in touch” form.

The Ultrasonic Acoustic Imaging Detection System (UAIDS) is developed by CRYSOUND and has already been deployed in multiple coal chemical, petrochemical and natural gas facilities. It is used for online leak monitoring in high‑risk areas. This article is written by the UAIDS project team at CRYSOUND based on real‑world deployment and operation experience. In a straightforward way, we will explain why such a system is needed, how it works in principle, what actually changes after it is put into service on site, and what it can and cannot do. Why is traditional leak inspection so difficult? In petrochemical plants, natural gas stations, coal chemical complexes and hazardous chemical storage yards, everyone understands how sensitive the word “leak” is. What really makes life hard is that many critical points are located high above ground, on pipe racks or at the tops of towers. In the past, finding a small leak at height usually meant going through a process like this: • Erect scaffolding or use a man‑lift and spend hours going up and down; • Climb around the pipe racks with soap solution or portable instruments in hand; • In winter, hands are frozen stiff; in summer, clothes are soaked with sweat, and even after checking a full round, people still worry: “There are so many valves and flanges, did we miss something?” To sum up, traditional leak inspection at such sites has several persistent pain points: • High locations: pipe racks at 20 meters or tower tops are hard to reach. Temporary access equipment is costly and high‑risk to use. • Very quiet leaks: the ultrasonic signals generated by small leaks are drowned in the noise of pumps and fans, and are practically impossible to hear with the human ear. • Invisible leaks: in the early stage, leak flow is tiny. Soap solution doesn’t bubble, and the smell is faint. By the time you actually see stains or smell gas, the leak has usually spread. • Low efficiency: a single process area can easily have thousands of monitoring points. Manual “up and down” inspection is mostly spot‑checking, and it is very hard to achieve truly continuous and full coverage. Traditional electrochemical, infrared and laser‑based detection methods are essentially point or line monitoring: • Measuring at a fixed point to see whether the concentration exceeds a threshold; • Watching along a single optical path to see whether any gas crosses it. What operators actually want, however, is not only to know whether a leak exists, but also to see clearly, over a wide area, exactly where the leak is occurring. That is precisely the problem that the ultrasonic acoustic imaging leak detection system (UAIDS) is designed to solve. UAIDS: Turning “inaudible leak noise” into colorful soundmap on the screen Basic principle: pressurized gas leak → ultrasonic signal → colorful soundmap on the image When pressurized gas escapes through valve gaps, tiny flange cracks or weld defects, it interacts with the surrounding air and produces intense turbulence, creating a class of ultrasonic signals with distinct characteristics: • The greater the leak rate, the stronger the ultrasonic signal; • The higher the pressure difference, the more pronounced the acoustic characteristics; • These signals are quite different from the lower‑frequency mechanical noise of motors and pumps, which makes it possible to pick them out from the background. What UAIDS does is to convert this “inaudible sound” into “visible images” in a smart way: • A multi‑channel ultrasonic sensor array is used to acquire ultrasonic signals simultaneously from multiple directions; • At the front end, amplification, filtering and denoising are performed to remove electromagnetic interference and low‑frequency background noise as much as possible; • Phase and amplitude differences between channels are analyzed to estimate the spatial distribution of sound energy and to infer from which direction and which area the leak noise is coming; • The sound energy distribution is mapped into a two‑dimensional “heat map” and overlaid onto the live video image from the field. In the end, the location with the strongest leak signal will appear as a red‑yellow‑green “cloud” on the display. For operators, the effect is very intuitive: wherever a cloud appears on the image, that is where something looks suspicious.  Engineering parameters: how far and how small can it detect? Based on field tests and joint calibration results from multiple online projects, UAIDS exhibits the following typical capabilities in engineering applications: Recommended detection distance: 0.5–50 m. Within roughly 1–30 m, the system achieves better signal‑to‑noise ratio and imaging performance for small leaks. Operating frequency range: UAIDS operates in the ultrasonic band (above 20 kHz). A band‑pass filter is used to select the leakage characteristic band (typically 20–40 kHz), effectively suppressing audible‑range and low‑frequency mechanical noise. Minimum detectable leak rate / orifice size (for typical conditions): Under a minimum pressure difference of about 0.6 MPa, UAIDS can provide visual detection for early‑stage leaks around the 0.1 mm scale at valve gaps and flange micro‑cracks. The actual sensitivity varies with gas type, pressure, background noise and sensor placement. Localization accuracy: Within the recommended detection distance, UAIDS can provide leak localization with approximately centimeter‑level accuracy. Combined with the video image, it can effectively point to a specific piece of equipment or flange area on the screen. These values are not rigid, unchanging limits, but rather typical engineering‑level performance verified across multiple real‑world projects. Protection rating: UAIDS has passed Ex ib IIC T4 Gb explosion‑proof certification and IP66 ingress protection tests, making it suitable for long‑term deployment in typical hazardous areas. System architecture: more than a single sensor—it is a complete online system UAIDS is not just a “smart sensor”. It is a complete online monitoring system that can roughly be broken down into three layers: Front‑end sensing layer: Pan‑tilt ultrasonic imaging leak detectors are deployed on site. They “listen” for leaks, capture the video image, and output the colored acoustic image. The pan‑tilt unit can rotate and tilt to scan a wide area. Mid‑tier storage layer: NVR and other storage equipment receive data from the front‑end devices, storing video, acoustic images and alarm records completely for later playback and incident analysis. Back‑end management layer: VMS and other management platforms connect to multiple front‑end devices, performing unified device management, detection control, alarm display and report generation, and presenting all data centrally on the control room video wall. In short: • The front end “sees” the leak point; • The mid‑tier “remembers” the process; • The back end “manages the whole site on one screen.” A typical site: from climbing pipe racks to watching colored clouds Let us take a typical coal chemical unit in Ningxia as an example. In this facility, 11 UAIDS units have been installed, covering gasifiers, heaters, tank farms and pipe racks. We can look at how day‑to‑day work has changed after UAIDS was introduced. Before the retrofit: six people climbing for half a day and still feeling unsure In a typical gasifier area, there are many high‑temperature and high‑pressure pipelines, valves and flanges inside the unit. Many key points are located around 20 meters above ground. The media are mostly flammable or toxic gases, so any leak not only wastes feedstock but also poses risks to personnel safety and plant stability. Previously, inspection was carried out roughly as follows: • Several inspectors and maintenance technicians would be assigned, scaffolding or access platforms would be prepared, and then they would go up onto the pipe racks; • With soap solution and portable detectors in hand, they would walk along the racks and platforms, checking each flange and valve one by one; • A single round could easily take half a day. During major inspections or special campaigns, they might have to repeat this work for days in a row. Front‑line staff described this mode in three words: “tiring, slow, and worrying.” Tiring: repeatedly climbing at height and twisting into awkward positions to look and listen close to equipment; Slow: in an area with dozens or hundreds of points, checking each one by one takes a long time; Worrying: with high background noise and many points, people always feel that eyes and ears alone may miss subtle issues. During the retrofit: letting the pan‑tilt unit “sweep the area” every day After assessing leak risks and inspection workload, we worked with the client to deploy several pan‑tilt ultrasonic imaging leak detectors at different platform elevations and connect them to UAIDS: • High‑level pan‑tilt units cover key areas such as gasifier heads and pulverized coal lines; • Mid‑level units cover lock hoppers, heat‑tracing lines, and dense clusters of flanges and valves; • Low‑level units cover feed tanks and ground‑level pipelines. Setting patrol routes and presets For each pan‑tilt unit, several preset views are configured—for example, along a specific pipe rack, a group of flanges, or a particular platform area. Patrol cycles are set according to process sections and risk levels, with higher‑risk areas scanned more frequently. Connecting to the central control system All acoustic images and alarm information from the front‑end devices are fed into the UAIDS management platform. On the control room video wall, operators can see an overview of the unit, the colored cloud images, and the alarm list at the same time. From then on, the devices basically follow the configured strategy and automatically “sweep the area” every day: • Each pan‑tilt unit rotates and tilts along its preset route, scanning key areas at each elevation; • Once characteristic ultrasonic leak signals appear at a certain location, a cloud will pop up at the corresponding position on the screen; • When operators in the control room see an abnormal cloud, they can immediately notify maintenance, who go straight to the indicated valve or flange to verify and fix the problem. After the retrofit: from “people hunting for problems” to “problems showing up on their own” After a period of operation, feedback from the site has mainly focused on three aspects: Fewer high‑level work operations Where previously 2–3 comprehensive high‑level inspection rounds per month were needed, they have now been reduced to seasonal campaigns plus on‑demand checks when abnormal clouds appear. High‑level work is much more focused on specific issues, and overall frequency has clearly dropped. Problems are found earlier and at a smaller scale In the past, many small leaks were only noticed when people smelled something or saw visible signs. Now, as soon as a leak reaches the detectable threshold, anomalies can appear on the cloud image in advance, allowing corrective actions to be taken earlier. Maintenance is more efficient Previously, when someone reported “it smells like gas in that area,” maintenance teams had to check dozens of flanges and valves one by one. Now, UAIDS directly marks which piece of equipment shows a strong acoustic anomaly on the screen, so technicians can take their work orders and go straight to the target region. Front‑line staff came up with a vivid summary: “In the past, we went around looking for problems; now, the problems show up on the screen by themselves.” This, in essence, is the change from climbing pipe racks to watching colored clouds. What can UAIDS do—and what can it not do? From a safety and engineering perspective, understanding the system’s boundaries is very important—this is being responsible both to the plant and to the system itself. What UAIDS is particularly good at Wide‑area online monitoring of high‑level and high‑risk zones By combining pan‑tilt units with sensor arrays, UAIDS can perform area coverage scans within approximately 0.5–50 m, making it especially suitable for 20 m pipe racks, tower tops and other locations where frequent manual access is difficult.  Visual localization UAIDS not only tells you that “there is a leak”, but also shows a cloud directly on the image to indicate where it is. With centimeter‑level localization accuracy, it can quickly narrow down to a specific piece of equipment or flange area. Around‑the‑clock monitoring UAIDS can operate online 24/7, greatly reducing the dependence on “someone just happening to walk by that point” at the right time. Compared with methods that rely on gas concentration build‑up, UAIDS is less affected by wind dispersing the gas, because it focuses on the ultrasonic signal generated by the jet itself, rather than on concentration readings at a single point. Reducing high‑level work and repetitive inspections By shifting from “frequent high‑level inspections” to “going up only when an abnormal cloud appears,” UAIDS helps reduce the workload and risk of working at height while improving overall inspection efficiency. What UAIDS cannot do: limitations we need to acknowledge honestly It cannot “see” leaks that are completely blocked The ultrasonic leakage signal can only be effectively detected and imaged when it is able to propagate to the ultrasonic sensor array. If the leak source is completely blocked by structural components or thick‑walled shells along the path, the array will receive much weaker, or even no, leak signal. Such areas need to be compensated by reasonable sensor placement, multi‑angle coverage or other complementary detection methods. Strong ultrasonic interference sources require special design Examples include process blow‑off points, steam vents that are open for long periods, and high‑frequency pneumatic devices, all of which can generate ultrasonic signatures similar to leaks. For these points, on‑site noise spectrum analysis is usually carried out during project design, and measures such as regional masking or logic filtering are introduced.  UAIDS is not a universal replacement, but a powerful complement For some scenarios where gas concentration itself must be monitored—such as toxic gas alarms in occupied areas—electrochemical, infrared and laser‑based sensors are still necessary. UAIDS is better suited to building a “sonic radar network” that lights up leak risks on the screen as early as possible. If we think of the entire leak‑monitoring setup as a team: • Concentration sensors are responsible for “defending the bottom line” (whether concentration exceeds the limit); • UAIDS is like an “early scout,” indicating where suspicious jets may be occurring and reminding you to take a closer look. Conclusion: let the system see the problem first so people can solve it more safely With an ultrasonic imaging leak detection system like UAIDS in place, the way work is done can change fundamentally: • The system scans the unit along preset routes every day; • Once a colored cloud appears on the display, personnel take their work orders and go up in a targeted way to deal with the issue; • High‑level work becomes more focused and less frequent, and many leaks can be resolved before they cause noticeable impact. For industries such as petrochemicals, natural gas and coal chemicals, UAIDS is not a flashy new gadget, but a way to identify leaks earlier, organize inspections more safely and manage risk more systematically. It is important to emphasize that UAIDS is not a replacement for all traditional detection techniques, but an important piece of the puzzle. In actual projects, we usually combine UAIDS with concentration detection, process interlocks and manual inspections, using a layered defense approach to improve overall leak‑control capability. If your site is facing issues such as many high‑level points with frequent scaffolding, late detection and slow troubleshooting of small leaks, or heavy inspection pressure at night and in bad weather, you may want to consider deploying an ultrasonic imaging leak detection system like UAIDS—letting problems first appear clearly on the screen so that people can address them more calmly and safely. To discuss your application or see whether UAIDS is a fit, please get in touch via our Get in Touch form.

A data acquisition system (DAQ) is the measurement front end: it converts analog sensor outputs—such as voltage, current, and charge—into digital data. The signal is first conditioned (amplification, filtering, isolation, IEPE excitation, etc.) and then fed to an ADC, where it is digitized at the specified sampling rate and resolution; software subsequently handles visualization, storage, and analysis. This article systematically reviews common DAQ form factors, including PCIe/PXI plug-in cards, external USB/Ethernet/Thunderbolt devices, integrated data recorders, and modular distributed systems. It also summarizes key selection criteria—signal compatibility, channel headroom and scalability, sampling rate and anti-aliasing filtering, dynamic range, THD+N, clock synchronization and inter-channel delay, as well as delivery and after-sales support—to help readers quickly build a clear understanding of DAQ systems. Why Data Acquisition Matters？ In the real world, physical stimuli such as temperature, sound, and vibration are everywhere. We can sense them directly; in a sense, the human body itself is a “data acquisition system”: our senses act like sensors that capture signals, the nervous system handles transmission and encoding, the brain fuses and analyzes the information to make decisions, and muscles execute actions—forming a closed feedback loop. Progress in science and engineering ultimately comes from observing, understanding, and validating the world with more reliable methods. Physical quantities such as temperature, sound pressure, vibration, stress, and voltage are the primary carriers of information. However, human perception is subjective and cannot quantify these changes accurately and repeatably; and in high-current, high-temperature, high-stress, or high-SPL environments, direct exposure can even cause irreversible harm. To enable measurement that is quantifiable, recordable, and safer, data acquisition systems (DAQ) came into being. Put simply, a data acquisition system (DAQ) is an analog front end that converts a sensor’s analog output (voltage/current/charge, etc.) into digital data at a defined sampling rate and resolution, and hands it to software for display, logging, and analysis (typically with the required signal conditioning). It helps engineers see problems more clearly—and solve them. In today’s development cycles—from cars and aircraft to consumer electronics—it’s difficult to validate performance, safety, and reliability efficiently without data acquisition. In durability testing, DAQ records cyclic load and strain for fatigue-life analysis; in noise control, synchronous multi-point acquisition of vibration and sound pressure helps identify noise sources and transmission paths. This quantitative capability is what provides a scientific basis for engineering improvements. DAQ applications span a wide range of fields: Automotive NVH and mechanical vibration testing: Used to acquire body vibration, noise, engine balance, structural modal data, and more—helping engineers improve vehicle ride comfort. Audio testing: In the development and production of speakers, microphones, headphones, and other audio devices, DAQ is used to measure frequency response, SPL, distortion, and more, to verify acoustic performance. Industrial automation and monitoring: DAQ is widely used for process monitoring, condition monitoring, and industrial control. For example, it acquires temperature, pressure, flow, and torque sensor signals to enable real-time monitoring and alarms, and it often must run continuously with high stability and strong immunity to interference. Research labs and education: From physics and biology experiments to seismic monitoring and weather observation, DAQ is a basic tool for capturing raw data. It makes data recording automated and digital, which simplifies downstream processing. As quality and performance requirements continue to rise across industries, DAQ has become an indispensable set of “eyes and ears,” giving engineers the ability to observe and interpret complex phenomena. Common DAQ Form Factors Depending on interface, level of integration, and the application, DAQ hardware comes in several common forms. Below are a few typical DAQ card/system categories: TypeForm factor / InterfaceAdvantagesLimitationsTypical ApplicationPlug-in DAQ cardPCIe / PXI / PXIeLow latency; high throughput; strong real-time performanceNot portable; requires chassis/industrial PC; expansion limited by platformFixed labs; rack systems; high-throughput acquisitionExternal DAQ deviceUSB / Ethernet / ThunderboltPortable; fast setup; laptop-friendlyBandwidth/latency depends on interface; driver stability is critical; mind power and cablingField testing; mobile measurements; general-purpose DAQIntegrated data recorderBuilt-in battery/storage/display (standalone)Ready out of the box; easy in the field; straightforward offline loggingChannel count/algorithms often limited; weaker expandability; post-processing depends on exportPatrol inspection; quick diagnostics; long-duration offline loggingModular distributed systemMainframe + modules; network expansion (synchronized)Mix signal types as needed; easy channel scaling; strong synchronizationPlanning matters: sync/clock/cabling; system design becomes more important at scaleSynchronized Multi-Physics Measurement;High-Channel-Count Scalability;Distributed, Multi-Site Testing Plug-in DAQ cards (internal): These are boards installed inside a computer, with typical interfaces such as PCI, PCIe, and PXI (CompactPCI). They plug directly into the PC/chassis bus and are powered and controlled by the host, providing high bandwidth and strong real-time performance for high-throughput applications in desktop or industrial PC environments. The trade-off is portability—these are usually used in fixed labs or rack systems. External DAQ devices (modules): DAQ hardware that connects to a computer via USB, Ethernet, Thunderbolt, and similar interfaces. USB DAQ is common—compact, plug-and-play, and well-suited to laptops and field testing. Ethernet/network DAQ enables longer cable runs and multi-device connections. External units are generally portable with their own enclosure, but high-end models may be somewhat limited in real-time performance by interface bandwidth (USB latency is typically higher than PCIe). Portable / integrated data recorders: These integrate the DAQ hardware with an embedded computer, display, and storage to form a standalone instrument. They’re convenient in the field and can acquire, log, and do basic analysis without an external PC. Examples include portable vibration acquisition/analyzer units with tablet-style displays and handheld multi-channel recorders. They are typically optimized for specific applications, ready to use out of the box, and well-suited for mobile measurements or quick on-site diagnostics. Modular distributed DAQ system platform: Built from multiple acquisition modules and a main controller/chassis, allowing flexible channel scaling and mixing of different function modules. Each module handles a certain signal type or channel count and connects to the controller (or directly to a PC) over a high-speed, time-synchronized network (e.g., EtherCAT, Ethernet/PTP). This architecture offers very high scalability and distributed measurement capability; modules can be placed close to the test article to reduce sensor cabling. For example, CRYSOUND’s SonoDAQ is a modular platform: each mainframe supports multiple modules and can be expanded via daisy-chain or star topology to thousands of channels. Modular systems are a strong fit for large-scale, cross-area synchronized measurement. What Makes Up a DAQ System? A complete data acquisition system typically includes the following key building blocks: Sensors: The front end that converts physical phenomena into electrical signals—for example, microphones that convert sound pressure to voltage, accelerometers that convert acceleration to charge/voltage, strain gauges that convert force to resistance change, and thermocouples for temperature measurement; Signal conditioning: Electronics between the sensor and the DAQ ADC that adapts and optimizes the signal.Typical functions include gain/attenuation (scaling signal amplitude into the ADC input range), filtering (e.g., anti-aliasing low-pass filtering to remove noise/high-frequency content), isolation (signal/power isolation for noise reduction and protection), and sensor excitation (providing power to active sensors, such as constant-current sources for IEPE sensors). Analog-to-digital converter (ADC): The core component that converts continuous analog signals into discrete digital samples at the configured sampling rate and resolution. Sampling rate sets the usable bandwidth (it must satisfy Nyquist and include margin for the anti-aliasing filter transition band), while resolution (bit depth) affects quantization step size and usable dynamic range. Many DAQ products use 16-bit or 24-bit ADCs; in high-dynamic-range acoustic/vibration front ends (such as platforms like SonoDAQ), you may also see 32-bit data output/processing paths to better cover wide ranges and weak signals (depending on the specific implementation and how the specs are defined). Data interface and storage: The ADC’s digital data must be delivered to a computer or storage media. Plug-in DAQ writes directly into host memory over the system bus. USB/Ethernet DAQ streams data to PC software through a driver. In addition to USB/Ethernet/wireless data transfer, SonoDAQ also supports real-time logging to an onboard SD card, allowing standalone recording without a PC—useful as protection against link interruptions or for long-duration unattended acquisition. Host PC and software: This is the back end of a DAQ system. Most modern DAQ relies on a computer and software for visualization, logging, and analysis. Acquisition software sets sampling parameters, controls the measurement, displays waveforms in real time, and processes data for results and reporting. Different vendors provide their own platforms (e.g., OpenTest, NI LabVIEW/DAQmx, DewesoftX, HBK BK Connect). Software usability and capability directly impact productivity. In addition, CRYSOUND’s OpenTest supports protocols such as openDAQ and ASIO, enabling configuration with multiple DAQ systems. What Specs Matter When Selecting a DAQ? Three common selection pitfalls: Focusing only on “sampling rate / bit depth” while ignoring front-end noise, range matching, anti-aliasing filtering, and synchronization metrics: the data may “look like it’s there,” but the analysis is unstable and not repeatable. Sizing channel count to “just enough” with no headroom: once you add measurement points, you’re forced to replace the whole system or stack a second system—increasing cost and integration effort. Focusing only on hardware while ignoring software and workflow: configuration, real-time monitoring, batch testing, report export, and protocol compatibility (openDAQ/ASIO, etc.) directly determine throughput. What you should evaluate: Signal types to acquire: In selection, clearly defining your signal types is the first step. Acoustic/vibration measurements are very different from stress, temperature, and voltage measurements. Traditional systems often support only a subset of signal types—for example, only sound pressure and acceleration—so when the requirement expands to temperature, you may need a second system, which increases budget and adds integration/synchronization complexity. SonoDAQ uses a modular platform approach: by inserting the required signal-type modules, you can expand capability within one system and run synchronized multi-physics tests—configuring what you need in one platform. Channel count and scalability: First determine how many signals you need to acquire and choose a DAQ with enough analog input channels (or a system that can expand). It’s best to leave some margin for future points—for example, if you need 12 channels today, consider 16+ channels. Equally important is scalability: SonoDAQ can be synchronized across multiple units to scale to hundreds or even thousands of channels while maintaining inter-channel acquisition skew < 100 ns, which suits large-scale testing. By contrast, fixed-channel devices cannot be expanded once you exceed capacity, forcing a replacement and increasing cost. Match sampling rate to signal bandwidth: start with the highest frequency/bandwidth of interest. The baseline is Nyquist (sampling rate > 2× the highest frequency). In practice, you also need margin for the anti-aliasing filter transition band, so many projects start at 2.5–5× bandwidth and then fine-tune based on the analysis method (FFT, octave bands, order tracking, etc.). For example, if engine vibration content tops out at 1 kHz, you might start at 5.12 kS/s or higher; for speech/acoustics that needs to cover 20 kHz, common choices are 51.2 kS/s or 96 kS/s. In short: base it on the spectrum, keep some margin, and align it with your filtering and analysis. Measurement accuracy and dynamic range: If your application needs to resolve weak signals while also covering large signal swings—for example, NVH tests often need to capture very low noise in quiet conditions and also record high SPL under strong excitation—you need a high-dynamic-range, high-resolution DAQ (24-bit ADC or higher, dynamic range > 120 dB). For audio testing, where distortion and noise floor matter and you want the DAQ’s self-noise to be well below the DUT, choose a low-noise, high-SNR front end and check vendor specs such as THD+N. Environment and use constraints: Think about where the DAQ will be used: on a lab bench, on the factory floor, or outdoors in the field. If you need to travel frequently or test on a vehicle, a portable/rugged DAQ is usually a better fit.For scenarios without stable power for long periods, built-in battery capability and battery runtime become critical. Lead time and after-sales support: After you define the procurement need, delivery lead time is a practical factor you can’t ignore. If your schedule is tight, a 2–3 month lead time can directly delay project kickoff and execution, so evaluate the supplier’s delivery commitment. Support is equally important: training, responsiveness when issues occur, and whether remote or on-site assistance is available. Also review warranty terms, software upgrade policy, and support response mechanisms—these directly affect long-term system stability and overall project efficiency. With the above steps, you can narrow down the DAQ characteristics that fit your application and make a defensible choice from a crowded product list. In short: start from requirements, focus on the key specs, plan for future expansion, and don’t ignore vendor maturity and support. Choose the right tool, and testing becomes far more efficient. FAQ Q: Can I use a sound card as a DAQ? A: For a small number of audio channels where synchronization/range/calibration requirements are not strict, a sound card can “work” at a basic level. But in engineering test work, common issues are: no IEPE excitation, insufficient input range and noise floor, uncontrolled channel-to-channel sync, and driver latency that is high and unstable. If you need repeatable, traceable test data, use a professional DAQ front end. Q: What’s the difference between a DAQ and an oscilloscope? A: An oscilloscope is more of an electronics debugging tool—great for capturing transients and doing quick troubleshooting. A DAQ is more of a long-duration, multi-channel, time-synchronized acquisition and analysis system, with an emphasis on channel scalability, synchronization consistency, long-term stability, and data management. Q: How do I choose the sampling rate? A: Start from the highest frequency/bandwidth of interest and meet Nyquist (>2× fmax) as a baseline. In practice, also account for the anti-aliasing filter transition band and your analysis method; starting at 2.5–5× bandwidth is usually safer. If you’re unsure, prioritize proper filtering and dynamic range first, then optimize sampling rate. Q: What is IEPE, and when do I need it? A: IEPE is a constant-current excitation scheme used by sensors such as accelerometers and IEPE measurement microphones, with power and signal on the same cable. If you use IEPE sensors, your DAQ front end must support IEPE excitation, appropriate isolation/grounding strategy, and suitable input range and bandwidth. Q: What should I check for multi-channel / multi-device synchronization? A: Focus on three things: a common clock source (external clock/PTP/GPS, etc.), channel-to-channel sampling skew/delay, and trigger/alignment strategy. For NVH, array measurements, and structural modal testing, sync performance often matters more than single-channel specs. Q: How do I estimate channel count—and should I leave headroom? A: List the “must-measure” signals and points first, then add auxiliary channels such as tach/trigger/temperature. A good rule is to reserve at least 20%–30% headroom, or choose a modular platform that scales, so you’re not forced to replace the system when points get added. If you’d like to learn more about the latest intelligent sound & vibration data acquisition system, SonoDAQ, from CRYSOUND, including its key features, typical application scenarios, and common configuration options, please fill out the Get in touch form below to contact the CRYSOUND team.  You’re also welcome to reach out to the CRYSOUND team. Based on your constraints—such as signal types, channel count, sampling rate/bandwidth, synchronization requirements, and on-site environmental conditions—we can provide a product demo and practical configuration recommendations.