Near-field Acoustic Holography 1024 Array

Microscopic low-frequency precision measurement—solving NVH challenges at the root.

Introduction

In whole-vehicle and component NVH development, low-frequency noise (such as motor electromagnetic noise, chassis booming, and bearing faults) has always been one of the most intractable problems. Constrained by the physical diffraction limit, conventional acoustic methods can yield only a huge “meter-level blurry” spot for low-frequency signals, making it impossible to precisely localize the excitation point—so optimization measures treat the symptom rather than the root cause.

The Near-field Acoustic Holography 1024 Array (NAH1024) has risen to meet this need. Relying on a 1024-channel high-density microphone array and the Near-field Acoustic Holography (NAH) algorithm, it breaks through the low-frequency wavelength limitation, elevating localization accuracy from the “meter level” to the centimeter level in a revolutionary leap, precisely locking onto the source of structural radiation and component noise, and providing three-dimensional quantitative acoustic analysis capability for complex components such as motors, battery packs, and chassis.

Core Advantages: From “Blurry Spot” to “Centimeter-Level Origin”

Breaking through the physical diffraction limit—low-frequency localization becomes precise and controllable

Adopting Near-field Acoustic Holography (NAH) technology, it performs dense acquisition in the near field of the sound source, capturing not only conventional propagating waves but also the evanescent waves that carry fine vibration information. Through inverse reconstruction of the complete sound field, it transcends the low-frequency wavelength limitation, carrying low-frequency localization resolution from the conventional “meter level” to the centimeter level and pointing directly to the fault excitation point.

1024-channel ultra-large planar array—millisecond-level “one-touch snapshot”

The array integrates 1024 high-density microphones, with an effective size of 960 mm×960 mm, capable of “wrapping” coverage of large components. A single trigger acquires full-field data synchronously, reducing the hours of conventional point-by-point scanning to just a few seconds, while eliminating the spatial localization error caused by repositioning the equipment and perfectly preserving the dynamic information of the transient sound field.

Accurate three-dimensional sound field reconstruction—data-driven quantitative analysis

Based on inverse computation with the NAH algorithm, it outputs high-resolution three-dimensional sound pressure / sound intensity contour maps, visualizing noise “hotspots” and energy flow paths. Engineers can directly use the quantitative data to guide structural optimization (such as rib layout and vibration isolation design), upgrading from “locating by listening” to “root-cause resolution through mechanism.”

Robust performance in strong reverberation environments

The near-field measurement approach effectively suppresses reverberation interference in complex cabins and workshops, ensuring high-signal-to-noise-ratio data across the 50 Hz–20 kHz frequency range. It is particularly suited to in-depth acoustic analysis within confined spaces such as motor assemblies, battery packs, and chassis suspensions.

Technical Principle: Capturing Evanescent Waves, Inversely Reconstructing the Sound Field

The core workflow of the NAH1024 consists of three steps:

1. Near-field sound pressure acquisition — 1024 microphones sample synchronously at an extremely short distance from the sound source, acquiring the complete sound pressure distribution including evanescent waves.

2. Inverse mathematical transform — using the spatial Fourier transform or the boundary element method, the sound source surface vibration velocity and the entire three-dimensional sound field are reconstructed from the measured data.

3. Accurate visual presentation — sound pressure / sound intensity colored contour maps are output at sub-wavelength resolution, with localization accuracy reaching the centimeter level, clearly displaying the excitation point position and radiation characteristics.

Typical Application Scenarios

• New energy vehicle electric drive assembly: precise identification of the excitation points of motor electromagnetic noise and bearing abnormal noise, optimizing gearbox and housing design.

• Power battery packs: monitoring structural radiation noise of battery modules, localizing abnormal vibration sources, and improving structural reliability.

• Chassis booming testing: analyzing the transmission paths of the suspension and subframe, and quantifying the contribution of low-frequency structural sound.

• Large complex component mapping: such as engine cylinder blocks and transmission housings—rapidly obtaining full-domain acoustic fingerprints and providing high-precision measured data for CAE model validation.

• Motorcycle / aerospace assemblies: transient sound pressure field and sound intensity “energy flow” vector tracing, supporting acoustic design of high-performance powertrains.

Technical Specifications

Notes: (1) The “frequency range 50 Hz – 20 kHz” figure is the microphone response range; the effective NAH spatial reconstruction band is bounded by the array’s spatial sampling limit, which for an array spacing of approximately 30 mm is approximately 5.7 kHz (see the appendix, Section 3, item 1). (2) The “imaging field of view: 360° horizontal × 90° vertical” figure is to be qualified—whether it denotes the native single-snapshot field of view of the planar array or the total coverage achievable with array repositioning (see the appendix, Section 3, item 2). (3) The sensitivity figure of −24 dB is quoted without a reference basis (e.g., re 1 V/Pa or dBFS), and the 65 dB SNR figure without specifying whether it is a per-channel, array-level, or system-level value (see the appendix, Section 3, item 5). (4) The sub-wavelength resolution cited in Section 3 is attainable under ideal near-field and high-signal-to-noise-ratio conditions (see the appendix, Section 3, item 3).

Building a Closed Intelligent NVH R&D Loop Together with the Holographic Sound Field Inspection Instrument

• The holographic sound field inspection instrument handles dead-zone-free troubleshooting and strong-noise decoupling in whole-vehicle-level macroscopic scenarios, rapidly locking onto the problem area.

• The NAH1024 handles low-frequency diagnosis and sound field dissection of microscopic complex structures at the component level, precisely localizing the excitation root cause.

Combining both strengths achieves a complete NVH data chain from “full-domain visualization” to “precise quantification,” supporting 100% digital, visualized decision-making by R&D teams.

Additional notes

• NAH core algorithm: breaking through conventional array resolution limits, with customizable development of core algorithms adapted to specific scenarios;

• Solid engineering validation: already applied to mainstream vehicle models of several automakers and to motorcycle powertrain testing;

• Customized services: array dimensions and channel counts can be expanded on demand, adapting to different components and test environments.

Conclusion

The Near-field Acoustic Holography 1024 Array—with a microscopic eye, deconstructing the mysteries of low frequency, so that NVH problems end at their root.