A rattle, boom, or vibration is a symptom, not a diagnosis — NVH engineering is the discipline of tracing it back to an actual cause.
NVH (Noise, Vibration, and Harshness) is the engineering discipline concerned with the sound and motion a vehicle's occupants actually perceive - not just whether a component meets a structural spec, but whether it's quiet, smooth, and comfortable in use. It spans three related but distinct concerns:
It's a genuinely standalone engineering discipline with its own instrumentation, measurement techniques, and analysis methods — accelerometers, microphones and sound-level meters, laser vibrometers, and modal/order analysis software, most of it with no dependency on the vehicle's electronic network at all.
Most NVH problems trace back to one of a few root mechanisms:
| Mechanism | Typical example |
|---|---|
| Rotating imbalance | A wheel, driveshaft, or engine component out of balance — produces vibration at a frequency tied directly to rotational speed |
| Resonance | A structure's natural frequency excited by an otherwise-normal input, amplifying it well beyond what the input alone would suggest |
| Looseness / contact | Two parts able to move against each other — the classic intermittent rattle, often load- or temperature-dependent |
| Aerodynamic | Wind noise from a panel gap, mirror, or seal at speed |
| Structure-borne transfer | A noise or vibration generated in one location (an engine mount, a subframe bush) transmitted through the vehicle's structure to somewhere it's perceived, well away from its actual source |
A large proportion of NVH events are tied to a rotating component's speed — a vibration that's exactly twice engine RPM points strongly at something on the crankshaft or a component geared 2:1 to it, for instance. Order analysis re-expresses a vibration or noise spectrum in terms of orders (multiples of a reference rotational speed, usually engine RPM) instead of a fixed frequency in Hz, so a "2nd order" vibration stays identifiable as 2nd order whether the engine is idling or at redline — a fixed Hz value wouldn't hold still under an RPM sweep.
NVH measurement, analysis, and diagnosis is one of ONAC's core service offerings in its own right — and where existing recordings or measurement data already exist, our remote analysis service covers NVH data just as it does vehicle network data, so a physical site visit isn't always required to get a useful diagnosis.