Knowledge

Glossary.

Terms of acoustic test technology – plainly explained. From natural frequency to psychoacoustics.

Test methods

Acoustic test technology: Umbrella term for inspection methods that use sound or vibration as carriers of information. Includes noise testing (NVH), material resonance analysis and process monitoring.
NVH (Noise, Vibration, Harshness): Discipline of noise and vibration analysis. Evaluates comfort behavior and anomalies on parts such as e-drives, transmissions or pumps.
Order analysis: Speed-normalized spectral analysis. Reveals tooth meshing frequencies, bearing damage and imbalances independent of the current speed.
Resonance analysis: Material testing method: the part is excited, the natural vibration behavior is measured. Cracks, micro-structure defects or material mix-ups become audible.

Airborne sound: Sound pressure in air, measured with microphones. Important for NVH evaluation, comfort testing and psychoacoustic analysis.
FFT (Fast Fourier Transform): Fast algorithm to compute the frequency spectrum of a time signal. Foundation of every acoustic evaluation. SonicTC uses hardware-accelerated FFT.
FRF (Frequency Response Function): Transfer function between excitation and response of a part. Identifies natural frequencies, damping and mode shapes.
Natural frequency: Frequency at which a body oscillates freely after excitation. Depends on geometry, mass and material properties. Cracks or microstructure defects measurably shift natural frequencies.
Spectrogram: Visualization of frequency content over time. Makes transient acoustic events visible – e.g. start-up, shifting or braking sounds.
Structure-borne sound: Vibrations that propagate in solid bodies. Captured with accelerometers or laser vibrometers – ideal for robust inline testing.

False reject rate: Share of OK parts incorrectly classified as not OK. Target in series testing: <1 %. Key metric of discrimination.
Psychoacoustics: Science of subjective perception of sound. Metrics such as loudness, sharpness or roughness make sound quality objectively measurable.
Slip rate: Share of NOK parts incorrectly classified as OK. Safety-relevant – must approach zero in series testing.

End-of-line (EOL): Final inspection station at the end of a production line. Pass/fail decision is made here – acoustic EOL testing is 100 % capable.
Inline testing: Inspection directly within the production line without cycle time loss. Requirement: test time < cycle time. SonicTC typically achieves < 1 s.
TaaS – Testing-as-a-Service: Contract testing in the laboratory. Delivers fast feasibility results without investment in own hardware.

With SonicTC we made the jump from sampling to 100% inline testing – without replacing our existing hardware.

Dr. M. Hofmann Head of Quality Engineering · Tier-1 Automotive Supplier

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