When a part makes noise or vibrates, it transports information about its internal condition to the outside. Acoustic test technology makes this information measurable – objectively, reproducibly and within fractions of a second.

The basic principle in one sentence

Every mechanical change inside a part – a crack, a microstructure defect, a worn bearing, a loose magnet in the rotor – alters the vibration or noise behaviour. Whoever measures this behaviour and compares it with a reference can assess the condition non-destructively.

The three method families

RTE structures acoustic testing into three clearly delineated disciplines:

1. Noise testing (NVH)

Parts are tested in operation – an e-drive runs on a test bench, a water pump is loaded. Microphones and accelerometers capture airborne and structure-borne sound, software decomposes the signal into its frequency components (FFT) and compares the result against a specification or a trained AI model.

Typical applications: EOL testing on e-motors, comfort acoustics on seat adjusters, pump testing in series production.

2. Material resonance analysis

The part is briefly excited – e.g. by a hammer impulse or a loudspeaker. Natural frequencies are computed from the response. Cracks, microstructure variations or material mix-ups measurably shift these frequencies – and become detectable.

Typical applications: crack detection on brake discs, sorting of sintering grades, incoming-goods inspection for material mix-ups.

3. Process monitoring

Sensors on the tool or machine continuously capture vibration. Tool wear, tool break or faulty joining processes show up in the vibration pattern before scrap is produced.

Typical applications: early tool break detection on CNC machines, joining control for screw processes, condition monitoring on drives.

Differentiation from other NDT methods

  • Ultrasonic testing: local volume inspection with high resolution. Acoustic resonance analysis instead inspects the part holistically, in a fraction of a second.
  • Eddy current: limited to electrically conductive materials. Acoustic methods work on steel, ceramics, plastics, sintered parts and composites.
  • X-ray / CT: very high detail, but slow, expensive and with radiation safety overhead. Acoustic methods are orders of magnitude faster and suitable for 100 % inspection.
  • Visual / vision: sees only surfaces. Acoustics sees inside.

When acoustic testing pays off

  1. High volumes: when 100 % of parts must be tested, inspection speed (often < 1 s per part) is decisive.
  2. Internal defects: cracks, voids, micro-structure faults or material mix-ups are invisible from the outside.
  3. Functional assessment: when not a single dimension but the overall behaviour matters (e.g. "does the motor sound OK?").

Where to read further

Upcoming articles dive deeper into the maths (FFT, sampling theorem, window functions) and into concrete method comparisons (acoustics vs. ultrasound, acoustics vs. hardness testing, acoustics vs. vision). If you have a concrete test task, get in touch – an initial consultation is free.