Vehicle Noise

1. Definition and NVH Concept

Vehicle noise refers to the acoustic radiation generated by multiple sources—including the engine, drivetrain, tyres, body structure, and aerodynamics—during vehicle operation, which is transmitted into and outside the cabin via air or structural paths. In automotive engineering, vehicle noise, along with vibration and harshness, forms the NVH (Noise, Vibration, and Harshness) research framework, serving as a comprehensive benchmark for evaluating manufacturing quality and ride comfort. Statistics show that roughly one-third of all vehicle faults are NVH-related, with automakers dedicating up to nearly 20% of their total R&D expenditure to this field.

2. Main Noise Sources

Vehicle noise exhibits varying dominant characteristics depending on vehicle speed: engine noise is most noticeable at low speeds, tyre noise takes over at mid speeds, and wind noise becomes the primary source at high speeds.

Engine Noise: Subdivided into combustion noise, mechanical noise, and aerodynamic noise. Combustion noise is caused by rapid cylinder pressure spikes; due to higher in-cylinder pressures, diesel engines generally produce higher combustion noise than petrol units. Mechanical noise stems from the impact and vibration of moving components such as piston slap, gear meshing, and the valvetrain. Aerodynamic noise includes intake, exhaust, and cooling fan noise, with exhaust noise often being the most energetic and dominant noise source of an internal combustion engine.

Tyre Noise (Road Noise) : Generated by the interaction between tyres and the road surface, primarily driven by the air-pumping effect (where tread grooves and the road surface create enclosed cavities, compressing and releasing air as the tyre rolls), tyre carcass vibration, and impacts from uneven road surfaces. Road noise is characterised by low-frequency broadband sound; in electric vehicles (which lack engine masking effects), road noise becomes exceptionally prominent.

Aerodynamic Noise (Wind Noise) : During high-speed cruising, wind noise is produced by airflow friction across the bodywork, vortex turbulence around exterior protrusions (such as wing mirrors and A-pillars), and whistling through panel shutlines. The magnitude of wind noise increases proportionally to the square of vehicle speed, escalating significantly above 80 km/h.

Other Noise Sources: Drivetrain noise (gear meshing in the gearbox and final drive/axle), brake noise, structural body vibration radiation, and air-conditioning system aero-acoustics (mainly from the blower motor and air ducts) are also key contributors to cabin noise levels.

3. Noise Control Technologies

Automotive noise control is broadly categorised into passive noise reduction and active noise cancellation (ANC).

Passive Noise Reduction: A mature and traditional approach that blocks noise transmission paths using materials such as sound deadening pads, acoustic insulation foam, and cavity fillers. However, it adds vehicle kerb weight—compromising lightweighting goals—and has limited effectiveness in attenuating low-frequency noise.

Active Noise Cancellation (ANC) : Works by emitting anti-phase acoustic waves through the cabin speakers to cancel out unwanted noise. Road Noise Cancellation (RNC)  technology, refined over more than 30 years, is now featured in several production models. While it can reduce low-frequency peak noise below 500 Hz by over 10 dB, the overall cabin sound pressure level reduction in real-world applications typically ranges between 3 and 4 dBA. The GB/T 46098-2025 standard, "Performance Requirements and Test Methods for Automotive Active Noise Cancellation Systems", implemented in March 2026, establishes a unified benchmark for testing and evaluation.

4. Key Trends

• ANC Trickling Down to Mass-Market Models: With mature algorithms and advancing standardisation, ANC is expanding beyond premium luxury cars into mainstream family vehicles in the RM100,000 bracket.

• Heightened NVH Challenges in New Energy Vehicles (NEVs): With the absence of engine noise, tyre roar, wind rush, and HVAC blower noise become far more noticeable to occupants, demanding more sophisticated and meticulous NVH engineering.

• Continuous Refinement of Regulatory Standards: Automotive noise standard working groups are actively developing multiple new standards covering wind noise measurement, squeak and rattle evaluation, brake noise testing, and hybrid vehicle noise assessment.