The intricate relationship between human perception and vibrations spans a wide spectrum, encompassing various sensory experiences, including noise, physical sensations, and harshness.

These three descriptions of the sensation of vibration also merge into one another. If the frequency of vibrations is between 0.1 Hz and 20 Hz, they can be perceived by the human body and influence our well-being. If vibrations are somewhat higher in the frequency range, from approximately 20 Hz to 100 Hz, vibrations are both perceptible by the body and audible via the air and are classified as harshness. Since the perceptible vibrations decrease significantly from approximately 50-100 Hz, the frequency ranges from approximately 100 Hz to 20 kHz are referred to as noise, i.e. unpleasant airborne sound that we hear.

Modern NVH measurement involves the use of a multi-channel data acquisition system equipped with a sound level meter function. This technology aids in the identification of specific noise sources within the vehicle, such as engine noise, wind noise, tire noise, and other external sources, contributing to comprehensive noise analysis in cars.

Alongside quantitative measurements, subjective assessments from test drivers and passengers play a pivotal role in evaluating the overall comfort of the vehicle. Their feedback assists engineers in understanding human perception of NVH and guides them in implementing essential improvements, central to the process of automotive noise and vibration analysis.

Conducting real-world driving tests provides valuable insights into how a vehicle performs across diverse environments. Road tests are instrumental in evaluating the comprehensive NVH characteristics of the vehicle, allowing for the identification of potential issues that may not be apparent during laboratory testing. While lab testing and simulation are important steps, the actual road testing is crucial to the comprehensive analysis of NVH in automotive vehicles.

Overall, the accurate measurement and analysis of NVH are fundamental components of vehicle design and development, ensuring the delivery of high-quality, comfortable vehicles that meet the expectations of discerning consumers. Employing effective NVH testing methodologies enables automakers to bring superior, comfortable vehicles to the market, in line with the core principles of noise and vibration control in the automotive industry.

Vibrations in the automotive sector are a critical factor that affects both driving comfort and safety. They can be caused by bumps in the road or by the vehicle itself. Vibrations can lead to fatigue and loss of concentration and affect driving safety.

The vibration characteristics of a vehicle have a considerable influence on the subjective perception of driving comfort. However, these vibration characteristics are not only crucial for comfort, but also for the health of the occupants. Occupants can experience health problems, e.g. back pain, due to considerable vibration amplitudes and prolonged exposure if insufficient design and testing has been done for vibration comfort.

Primary sources of vibration in automobiles

The imbalance of the engine and drivetrain, the ignition of the cylinders in a combustion engine and the magnetic characteristics of the electric motor can lead to significant vibrations throughout the vehicle.

Measuring and analyzing these vibrations is often a complex task that requires both specialized analysis tools and knowledge of how to interpret the results. Here are some of the common methods for measurement and analysis:

Speed sensors are used to measure the rotational speed of the motor and other moving parts in the drivetrain. This data allows conclusions to be drawn about how the vibrations change with speed. The vibrations themselves are usually measured using acceleration sensors, which are attached to various points on the engine and drivetrain and provide information on the amplitude and frequency of the vibrations. The recorded signals are analyzed online as frequency spectrum or order spectrum over the speed and visualized. In this way, engineers and mechanics can determine the causes of vibrations and localize potential problem areas.

Bumps in the road cause vibrations that are absorbed by the wheels and chassis. The quality of the dampers, springs and chassis structure determines how these vibrations are absorbed and damped. The measurement and analysis of chassis vibrations is essential for assessing ride comfort, handling and the overall dynamic behavior of a vehicle.

Triaxial accelerometers are commonly used sensors for measuring chassis vibrations. These sensors detect accelerations and can be mounted at various points on the chassis. Often the interest of the vibrations is in the frequency and amplitude, which is calculated using the averaged FFT spectrum. The frequency spectrum provides information about the dominant frequencies of the vibrations, which can be correlated with specific vehicle components or road conditions.

How do vibrations affect the human body? The vibration level in vehicles is measured in accordance with ISO 2631. This standard provides information on the load of the vibration on the human body as whole-body vibrations.

Wheel force sensors can be used to determine the dynamic forces introduced into the vehicle by the road surface.

> Learn More about Wheel Force Sensors

Aerodynamic vibrations are caused by the interaction between aeroelastic forces and the structural dynamic properties of a vehicle or a vehicle component. These can be, for example, vehicle wing mirrors, spoilers or the roof, which are stimulated to vibrate by the air flow. These turbulent flows are pressure fluctuations in the air and are measured using sound pressure microphones. Care must be taken to ensure that the microphones do not influence or even distort the vibrations. Ultra-Thin-Precision (UTP) microphones or surface microphones from GRAS are ideal for such measurements as they can be strategically placed on the vehicle and are easy to use.

The GRAS 48LX-1 UTP microphone has a height of only 1 mm and these microphones are also available in 4 channels (GRAS 48LX-4) and 8 channels UTP line array (GRAS 48LX-8) for measurements in boundary layers and turbulence.

> Learn More about GRAS UTP Microphones