NVH is an acronym for noise, vibration, and harshness. In the automotive world, it pertains to the measurement and
reduction of excess sound and vibration in vehicles. NVH is sometimes referred to as N&V, or just noise and
vibration. Car manufacturers focus on reducing NVH to improve the driving experience.
What’s the Difference Between Noise & Vibration?
When talking about noise and vibration, they’re often described in relation to particular frequencies. Noise usually
occurs in the frequency range of 30 to 4,000 Hz. It can be anything from squeaks and rattles to road noise.
Vibration is tactile, felt through humming, trembles, or other motions. Its frequency range is smaller, typically
occurring between 30 to 200 Hz. If you’ve ever felt a steering wheel shake or a car idling heavy, then you’ve
While noise and vibration are easily measured, harshness is a more relative term. Harshness is how noise and vibration
are felt by occupants inside a vehicle’s cabin, like when you accidentally hit a pothole.
What Causes NVH?
All the components that help make a car operate are also what contribute to NVH. These include the engine, exhaust,
drivetrain, and tires as well as the outside sound of air at high speeds. The main sources of NVH can be categorized
into three different types: aerodynamic, electrical, and mechanical.
Aerodynamics refers to the wind noise created when a vehicle is in motion. Disturbances in the path of the air can
create vibrations of the air particles and transmit the sound. Side mirrors, roof racks, and other design elements
can interrupt the airflow and create howling or whistling noises from the wind.
Electrical NVH is caused by a vehicle’s electrical components, such as the alternator or battery. Electrical noise is
often heard as a humming or whining sound and is less pronounced than other forms of NVH.
Mechanical noise is produced by the engine, drivetrain, brakes, and other mechanical components. Suspension systems
can be noisy, which is why some manufacturers use independent rear suspension (IRS)
systems rather than solid axles. Both multi-link and IRS systems work to isolate both the chassis and
steering column from road surfaces to reduce vibration.
Tires can also lead to a lot of road noise and vibration, which is why tire producers engineer tread patterns to be
quieter and provide a smoother ride.
How Can You Lower Your NVH?
Car manufacturers and engineers work diligently to reduce NVH as much as possible. But there are a few ways to lower
NVH yourself. You can reduce the strength at the source, or work on isolating and absorbing excess sound and
Reducing NVH at the Source
When it comes to reducing vibration, the suspension system plays a big part. As mentioned previously, using an IRS
can reduce road noise. If you have a solid axle, you can upgrade to an IRS system to reduce NVH and improve
If you’re experiencing a lot of wind noise, you can improve aerodynamics in a variety of ways. You can lower your
car, add side skirts or a rear spoiler, use narrower tires, remove the roof rack, and limit cargo weight. If you
have a truck, you can also install a tonneau
cover over the bed to reduce drag.
Mufflers and resonators help reduce the
sound level of your exhaust. If you’ve got a hole in your muffler or are experiencing drone at a certain RPM range,
then a new muffler or resonator can reduce excess or annoying noises caused by the exhaust.
Isolation & Absorption
Isolating and absorbing sound are other ways to reduce NVH. Isolators interrupt the vibration path. Absorption
materials, such as foam or dampers, help soak up noise and vibrations.
Another way multi-link and IRS systems reduce NVH is by isolating the suspension system from the chassis and steering
column. This helps improve ride quality and handling when you drive over bumps and dips in the road. Steering
dampers also go a long way to decrease vibration from uneven road surfaces.
Using rubber and polyurethane bushings instead of metal can also help isolate and reduce noise caused by the exhaust,
suspension, and engine components. The soft materials will also absorb unwanted vibrations.
Sound-deadening material helps isolate the cabin from outside noise. For instance, Jeep Wranglers are notorious for
being loud due to their boxy shape and open-air design. But there are ways to soundproof a Wrangler or whatever
car you may be driving. You can use rubber-like material or foam to provide more insulation as needed.
If your stock tires are too loud, you may find that switching tires can make a big difference. Tire manufacturers
design tread patterns specifically to reduce noise and vibration.
Why Is NVH Important for Electric Vehicles?
While you might think having a motor instead of an engine would reduce NVH, it actually makes noise more apparent.
You still have NVH due to the transmission, alternator, actuators, cooling fans, brakes, road noise, wind, and
tires. All these noises sound louder without the roar of an engine to muffle them. Because of this, the study and
measurement of NVH are increasingly important in automotive engineering.
Source: Science Direct, Driving, Echo Supply