In acoustic design and noise control, a material’s acoustic impedance characteristics are a key factor in determining “how it sounds.” By measuring parameters such as the absorption coefficient, reflection coefficient, specific acoustic impedance, and acoustic admittance, we can not only quantify a material’s ability to absorb and reflect sound, but also evaluate its performance in real-world applications—such as room reverberation time, noise-control effectiveness in equipment, and the acoustic comfort of products like automobiles and home appliances. Accurate acoustic impedance testing gives engineers solid evidence for material selection, structural optimization, and acoustic simulation, dramatically reducing trial-and-error costs and shifting acoustic design from experience-driven to data-driven.

Advantages of the Transfer-Function Method

Among the many acoustic impedance measurement methods, the transfer-function method is widely used thanks to its fast testing speed, high accuracy, and broad applicable frequency range. By placing two microphones inside an impedance tube and using the sound-pressure transfer function, one can back-calculate parameters such as the absorption coefficient, reflection coefficient, and specific acoustic impedance—without complicated sound-source calibration or overly idealized assumptions about the sound field. Compared with the traditional standing-wave ratio method, the transfer-function method depends less on operator experience, delivers more stable low-frequency measurements, and is easier to automate and post-process, making it well suited for R&D, material screening, and high-throughput quality inspection in industry.

CRYSOUND Integrated Test Solution

CRYSOUND provides a complete acoustic impedance testing solution. Built around the CRY6151B data acquisition unit, and combined with our in-house algorithms plus testing software and an impedance-tube hardware system, it delivers an integrated workflow—from equipment calibration and data acquisition to parameter calculation and report generation.

In terms of hardware configuration, we use a measurement chain optimized specifically for acoustic impedance testing. At the front end, two 1/4-inch pressure-field measurement microphones (CRY3402) are deployed. While ensuring a wide frequency range and wide dynamic range, they maintain excellent linearity and stability under high sound-pressure levels—making them ideal for precise measurements in the high-SPL sound field inside an impedance tube. At the back end, a CRY6151B data acquisition unit handles signal acquisition and output control, featuring low noise floor, stable output, and a clean, straightforward interface and operating logic.

On the software side, we provide a complete workflow covering calibration, measurement, analysis, and reporting—making the tedious yet critical steps in acoustic impedance testing both meticulous and easier for users. Before testing, the software guides users through input/output calibration to ensure the gain and phase of the excitation output and acquisition channels are under control. It then performs a signal-to-noise ratio (SNR) check, automatically evaluating whether the current test environment and hardware configuration meet the conditions for valid measurements, avoiding wasted time under low-SNR conditions.

To match the characteristics of the transfer-function method, the software integrates transfer-function calibration and dual-microphone acoustic-center distance calibration modules. Through dedicated calibration procedures, it automatically corrects inter-channel amplitude/phase errors and microphone acoustic-center position offsets, reducing high-frequency ripple and computational error at the source. It also supports flange-tube calibration, compensating for leakage and geometric deviations at flange connections so that reliable absorption-coefficient and acoustic-impedance results can still be obtained even under conditions close to real-world use. The entire workflow complies with the requirements of GB/T 18696.2-2002.

During actual measurements, the software supports multiple excitation types, including random noise and pseudo-random noise for rapid wideband scanning, as well as single-tone signals for precisely locating resonance frequencies and analyzing the relationship between impedance and sound speed — useful for material mechanism research or fine tuning. After the test, the data can be displayed in multiple band formats, and curves from different samples or operating conditions can be compared within the same interface. Users can view key parameter curves such as the absorption coefficient, reflection coefficient, and specific acoustic impedance, and can also automatically generate a test report that includes measurement conditions and result plots, greatly improving the efficiency and standardization of acoustic impedance testing.

Overall, acoustic impedance testing is both a “magnifying glass” for understanding a material’s acoustic properties and a “ruler” for translating acoustic design into engineering reality. With an optimized hardware chain (CRY3402 microphones + CRY6151B data acquisition unit) and an integrated software platform that combines calibration, measurement, analysis, and reporting, we aim to make acoustic impedance testing—once a highly specialized and complex task—controllable, visual, and repeatable, truly supporting product R&D, quality control, and acoustic-experience improvement for enterprises.

In industrial testing, research, and quality validation, data acquisition devices (DAQs / audio interfaces / measurement microphone front-ends) are the “front door” of the entire system. As technology and applications become more specialized, a wide variety of DAQ devices has emerged:

• High-precision front-ends designed specifically for acoustics and vibration
• General-purpose dynamic signal acquisition modules
• Common USB sound cards and measurement microphones

Hardware is not the bottleneck anymore. The real challenge is:

How do you connect, configure, and manage devices from different brands and protocols in one software platform?

OpenTest is built around this pain point. With an open, multi-protocol hardware access architecture, it turns acquisition from “isolated devices” into a unified platform, enabling cross-brand, multi-device data acquisition and analysis.

Multi-Protocol Hardware Access: Reducing Vendor Lock-In

OpenTest supports several mainstream connection methods. You can choose the appropriate protocol based on your hardware type and driver environment (actual compatibility depends on software version and device drivers):

• openDAQ – For open DAQ integration. Used to connect open hardware such as CRYSOUND SonoDAQ and manage channels and acquisition parameters in a unified way
• ASIO / WASAPI / MME / Core Audio – Mainstream audio interfaces on Windows and macOS, supporting professional audio interfaces and USB measurement microphones such as RME, Echo, miniDSP, etc.
• Other proprietary protocols – Can be added according to project requirements

This means you no longer need to be locked into a single hardware brand or a single piece of software. Existing devices can be brought smoothly under one platform for centralized management.

Multi-Device Collaboration: One Project, Many Acquisition Tasks

Complex tests often require multiple signal sources to be acquired together, for example:

• Dynamic signals such as microphones and accelerometers
• Operating parameters such as speed, temperature, pressure, torque
• Auxiliary audio paths for monitoring and playback

With OpenTest’s multi-protocol architecture, you can manage multiple devices within the same project. For NVH and structural testing, this kind of cross-device collaboration significantly reduces repetitive work like:

Recording in multiple software tools → exporting → manual time alignment → re-analysis

Getting Started: Connecting Devices Quickly

• Connect your data acquisition device to the PC running OpenTest
  • USB connection, or
  • Network connection (ensure the device and PC are on the same subnet)
• In the Hardware Setup panel, click the “+” icon in the upper-right corner. OpenTest will automatically scan for connected devices
• Check the devices you want to use and click Confirm to add them to the active device list
• Switch to the Channel Setup list, click the “+” icon in the upper-right corner, select the channels required for the current project (channels from different devices can be combined), and click Confirm to add them to the project
• Select the channels; OpenTest will automatically start real-time monitoring and analysis. You can then switch to different measurement modules according to your test needs

Presets + Fine Tuning: Easy to Start, Easy to Standardize

To help teams enter the testing state quickly, OpenTest supports a “presets + adjustments” configuration approach:

• Turn commonly used hardware parameters and acquisition settings into reusable templates
• Apply templates directly when creating a new project to avoid starting from scratch
• Still keep full flexibility to fine-tune settings for different operating conditions and devices

For production line or regression testing, templating adds an important benefit: uniform test conditions, comparable results, and traceable processes across time and across operators.

Logging and Monitoring: Designed for Long-Term Stability

For long-duration, multi-device acquisition, the worst case is discovering that something dropped out halfway. OpenTest provides observability features to address this:

• Device and channel status monitoring – Quickly detect disconnections, overloads, and abnormal inputs
• Operation and error logs – Record key actions and error events to support troubleshooting and process optimization

This is especially critical for continuous production testing and durability tests, significantly reducing the chance of “realizing halfway through that nothing was actually recorded.”

Typical Application Scenarios

• Acoustics and vibration R&D – Use the same platform to connect front-end DAQs and audio interfaces, quickly complete acquisition, analysis, and report generation
• Automotive NVH / structural testing – Acquire noise, vibration, and operating parameters together, minimizing cross-software alignment work
• Production line automated testing – Template-based configuration + monitoring/logging + automated reporting to improve consistency and traceability

OpenTest’s goal is not to make you replace all your hardware, but to bring your existing hardware together on one platform so that data acquisition becomes more efficient, more controllable, and much easier to standardize.

Visit www.opentest.com to learn more about OpenTest features and hardware options, or contact the CRYSOUND team for demos and application support.