Exploring Acoustics and Product Design

While industrial design traditionally spotlights the visual and tactile aesthetics of form, the realm of auditory characteristics remains largely uncharted territory for most product designers. Even instances where sound is a pivotal facet of a product, such as a radio’s auditory output, it often sees the decisions regarding acoustical attributes divorced from the overarching product design process.
Does sound warrant a significant role in the realm of product design? If so, how can product designers actively contribute to this auditory facet?

The recent shift from mere “product design” to the broader concept of “experience design” has ushered in a renewed emphasis on design transcending the confines of the product itself. This evolution mandates a comprehensive assessment of all facets of a product—its functionality, aesthetics, and even upkeep—through the lens of design. Similarly, ancillary experiences conveyed via advertising, packaging, instructions, technical support, etc., must consistently mirror a commensurate quality of experience. Essentially, the tenets of design must envelop a user’s or customer’s complete interaction across the entirety of a product’s life cycle.
Integrating the acoustical dimensions into the matter of the product experience constitutes an organic extension of the broader product/experience design paradigm. We can characterize the acoustical design of a product into three distinct components:

1. Undesirable Attributes: These pertain to sounds arising from product usage that are deemed undesirable, such as the wind-induced noise while driving a car or the intrusive hum from an electrical device.

2. Primary Acoustical Characteristics: These encompass the sounds generated by a product during its intended operation, be it through manual, mechanical, or electronic means. Examples include the decisive click of a light switch, the whir of a drill, the dial tone of a telephone, or the satisfying snap of a camera shutter.

3. Secondary Acoustical Characteristics: These represent sounds that a product emits beyond its fundamental usage—think of the auditory experience while unboxing or transporting the product.

In this article, we will take the first component: undesirable events in product operation

Low Frequency Noise in a Passengers Cabin

In real-world scenarios, the vibrational and acoustic characteristics of a car at low speeds is  predominantly an outcome of the interplay between engine and road surface irregularities. This induces vibrations across various components such as doors, roof, windshields, and floor panels.

There is however, a particularly unwanted element to this, and it’s the amplitude of acoustic responses in the passenger cabin that experiences significant escalation especially in the lower frequency range, due to noise emanating from these parts. Each of them exhibits its peak acoustic potency at its inherent frequencies, stimulated during the drive.

The distinct frequencies at which the engine operates can engender resonance in different elements, as each component possesses a unique resonance frequency. 

Our solution

The present study introduces an innovative approach aimed at comprehending the challenge. Our methodology consists of comprehensive laboratory examinations, dissecting the vibroacoustic environment automotive industry.

Employing an acoustic dynamometer equipped with simulated rugged road surfaces, we subjected the vehicle to testing. Concurrently, a laser vibrometer was employed to scrutinize resonant patterns at specific driving velocities.

Now, this groundwork opens avenues for potential extension into the realm of Finite Element Method (FEM) vibroacoustic simulations. This entails establishing correlations between simulation outcomes and findings derived from the distinct laboratory investigations, thereby fostering a cohesive research trajectory.

Addressing this matter needs a meticulously controlled environment capable of emulating real vehicular conditions: management of excitations, encompassing variables like road surfaces and driving scenarios, all enacted within a stable and controlled setting. Accompanied by the deployment of precise sound and vibration testing equipment, these factors make the undertaking such a study possible.

An integrated approach, encompassing both vibrational and acoustic responses of an automobile, has undergone comprehensive examination.

This study is an outline of KFB’s approach to the investigation and mitigation of  the aforementioned phenomenon. Our exploration is grounded in the use of a unique brand new test stand located in the Acoustic Research and Innovation Center (ARIC) by KFB Acoustics in Poland. This exceptional facility ingeniously fuses the capabilities of an acoustic dynamometer with those of a 3D laser Doppler vibrometer, seamlessly orchestrated through the intricate maneuvers of a scanning robot. The system is ensconced within a semi-anechoic chamber, meticulously tailored to foster an environment conducive to rigorous research endeavors. Furthermore, this chamber is fully equipped with a comprehensive sound and vibration acquisition system, adding an additional layer of precision to the investigative process.
The combination of our methodology and technical capabilities created extremely accurate Noise, Vibration, and Harshness (NVH) analysis, including:

1.  Low-Frequency Excitation: By simulating road irregularities, the vehicle’s suspension system is excited at low frequencies, enabling a meticulous observation of vibration behavior and response under conditions akin to real-world driving scenarios.
2. Structural Analysis: 3D laser vibrometer captures vibrations during intensive dynamometer tests. This dataset unveils the structural dynamics of vehicle components, shedding light on resonant frequencies and discerning the mode shapes that contribute to undesirable vibrations.
3.  Modal Analysis: The 3D laser vibrometer’s utility extends further to unraveling the modal structure of vehicle components. A spectrum of natural frequencies, mode shapes, and damping characteristics is unveiled. 
4.  Transfer Path Analysis (TPA): TPA delves into pathways through which vibrations and noise propagate from their source to receiver. By combining measurements from the 3D laser vibrometer with dynamometer inputs, a comprehensive understanding is gained.
5.  Acoustic Analysis: The 3D laser vibrometer takes on a role in acoustic analysis. It gathers data on surface vibrations that harmonize with recorded cabin noise, pinpointing areas contributing to excessive noise. This synchronization facilitates the design of noise-controlling measures—such as insulation and absorptive materials—to enhance passenger comfort.
6.  Tire Noise Analysis: The acoustic dyno creates a perfect environment to assess tire-road noise. Through methodical, stable and repetitive experimentation, the tire-road noise is deciphered, allowing tire noise patterns to be displayed in a clear manner and eliminated through design modifications.

Innovative NVH Analysis

In this scientific exploration, the collaborative potential of the Semi-anechoic Dynamometer facility and the 3D laser vibrometer emerges as an analytical toolset. It offers the capability to identify sources, unravel intricate structural dynamics, and devise tailored solutions to elevate vehicular comfort while addressing the challenges posed by noise and vibrations.

However, this marks just the inception. As empirical data takes center stage, researchers employ recorded noise and vibration measurements as analytical instruments. The pivotal step involves refining Finite Element Method (FEM) models, assessing low-frequency phenomena. Employing techniques such as spectral analysis, researchers uncover primary frequencies and underlying sources.

Summary

Throughout this scientific endeavour, correlations between low-frequency noise and vehicle characteristics—such as speed, engine RPM, and suspension attributes—come to the fore. The FEM study becomes a tool for unraveling the complexities of car vibroacoustic behavior, ultimately setting solutions for the reduction of noise and vibration. 

In the case of passenger or operator cabins, where comfort reigns supreme, this holistic approach unravels the intricacies and implications of low-frequency noise. It provides a foundation for innovative strategies aimed at mitigating discomfort, thereby fostering an environment of serenity and enhancing passenger well-being.