Which acoustic test method for which task?
Noise testing, resonance testing, process monitoring and modal testing compared – plus resonance test systems by excitation and system types by openness.
Acoustic resonance testing (ART) excites a part to natural vibrations and compares its resonance spectrum with references; cracks, shrinkage cavities, microstructural defects and material mix-ups shift the natural frequencies and are detected non-destructively.
Methods at a glance
Four acoustic methods cover different test tasks – from operating noise to material defects in the microstructure.
| Method | Test task | Test object | Excitation | Result | Cycle capability | Limits |
|---|---|---|---|---|---|---|
| Noise testing (NVH) | Evaluate noise and vibration quality objectively | E-motors, gearboxes, pumps, actuators | Operation of the part (run-up) | OK/NOK, orders, psychoacoustics | 100 % inline, OK/NOK in under 1 s | The part must be operated; ambient noise requires sound insulation |
| Acoustic resonance testing (ART) | Detect cracks, shrinkage cavities, microstructure defects, material mix-ups | Cast, sintered and ceramic parts | Impulse hammer, loudspeaker, piezo exciter | Resonance spectrum, OK/NOK | 100 % inline, OK/NOK in under 1 s | Evaluates the whole part but does not locate the defect; one configuration per part family |
| Acoustic process monitoring | Detect tool breakage, wear and joining errors | Machining, joining/pressing, welding, assembly | The process itself | Signal to the control | During the process, every part | The sensor must be close to the process; the part itself is assessed only indirectly |
| Modal test | Determine natural frequencies, damping and mode shapes | Individual parts, prototypes, reference parts | Impulse hammer, shaker | Modal parameters | Laboratory, not for series cycles | Effort per part is high; provides the basis for resonance testing |
Resonance test systems by excitation and acquisition
Resonance test systems differ mainly in how the part is excited and how the vibration is acquired. The choice depends on the part, the frequency range and the cycle.
| Excitation / acquisition | Strengths | Limits | Typical use |
|---|---|---|---|
| Impulse hammer, tapping actuator | Broadband excitation, simple and robust | Impact point and force must be reproducible | Series testing in cycle; mobile with the Sonic MLNR test hammer |
| Loudspeaker | Contactless excitation without wear | Lower excitation energy for heavy parts; ambient noise must be considered | Light and sensitive parts |
| Piezo exciter, shaker | Targeted excitation of defined frequency ranges | Coupling to the part required | Laboratory, modal test, special test stations |
| Microphone, accelerometer, laser vibrometer | Acquisition matched to the part; the laser vibrometer measures without contact | Accelerometers need contact, the laser vibrometer needs a line of sight | Pre-qualified sensor kits per test task |
System types compared
Besides the method, the system type determines how flexible a test system remains: for new variants, for retrofits and for access to the data.
| System type | Hardware dependency | Configurability | Retrofit | Data access |
|---|---|---|---|---|
| Closed turnkey system | Tied to the supplier’s hardware | Within the intended test tasks | Usually only with the same system | Via the supplier’s tools |
| Open platform (SonicTC) | Hardware-open: sensors from various manufacturers, data acquisition via NI-DAQmx and TwinCAT | Configure instead of programming | Upgrade existing systems with new test software and reuse mechanics and sensors | Results via PROFINET, OPC UA, EtherNet/IP, Modbus, TCP/IP or digital I/Os |
| In-house development | Freely selectable | Full freedom, but maintenance and documentation remain with the operator | Possible, with own effort | Complete, under own responsibility |
How acoustic methods relate to imaging methods
Acoustic methods complement X-ray/CT, ultrasound and eddy current testing rather than replacing them. Resonance testing evaluates the whole part in one step, without couplant and on steel, ceramics, plastics and sintered material. Imaging methods locate a defect in detail but are slower; eddy current is limited to conductive materials.
Frequently asked.
Which method is suitable for cracks in cast and sintered parts?
Acoustic resonance testing: cracks, shrinkage cavities and microstructure defects shift the natural frequencies. The part is excited and the spectrum compared with the reference – non-destructively and within the cycle.
Does acoustic testing replace X-ray or ultrasound?
No, it complements them: acoustic testing evaluates every part quickly and as a whole, while imaging methods locate the defect in detail when in doubt.
Can noise and resonance testing be combined on one platform?
Yes: SonicTC combines the modules SonicTC.NVH (noise testing), SonicTC.AT (resonance testing) and SonicTC.DSP (process monitoring) on one platform. Which module is needed depends on the part and the defect pattern.
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