Browse Topic: Exterior noise
Tire exterior noise has become increasingly critical in vehicle acoustics due to two key developments: updated pass-by noise regulations, which amplify the relative contribution of tire noise, and the rise of Battery Electric Vehicles (BEVs), which lack traditional powertrain noise. Design trends in BEVs—such as increased vehicle mass from battery packs and the widespread use of large-diameter, wide, low-profile tires—further intensify tire noise due to stiffer constructions and altered contact dynamics. A common method for predicting tire noise is the source-transfer-receiver model, where the tire is represented by a set of monopoles with volume velocity Q derived from near-field measurements. Acoustic propagation is modeled via p/Q transfer functions. Despite its simplifications, this approach is practical for vehicle development, enabling clear separation between source and transfer mechanisms and facilitating targeted noise control strategies. In previous work, we proposed a rigorous framework to optimize both the spatial distribution and strength of the monopole sources. Positions were identified using an L1-norm regularization via the Lasso algorithm, promoting sparsity and physical interpretability. Strengths were estimated using an L2-norm Tikhonov regularization, which stabilizes the solution against measurement noise. While the Tikhonov regularization parameter was previously tuned manually through trial and error, we now enhance predictive accuracy by selecting it via a cross-validation technique, ensuring a more robust and data-driven optimization. Besides this, compared to the previous work the approach here is validated for the prediction of both indoor and outdoor pass-by noise, as well as for multiple tire types providing different noise levels. Results demonstrate the method’s robustness, accuracy, and applicability for acoustic development in modern vehicle platforms.
Electric vehicle subsystems, including powertrains, electric motors, and gearboxes, pose new challenges in achieving stringent acoustic performance targets for both interior and exterior noise. These challenges are intensified by increasingly demanding customer expectations regarding interior acoustic comfort, which encompasses the reduction of intrusive noise sources and the enhancement of overall sound quality across a broad frequency spectrum. A primary concern associated with electric vehicles subsystems is the generation of high-frequency tonal noise, commonly referred to as whine noise, which can significantly impact acoustic performance and passenger comfort. High-frequency whine noise propagates through multiple transmission paths and can be effectively attenuated at the source through encapsulation strategies, which also contribute to broadband noise reduction across a wide frequency spectrum. To predict the acoustic performance of encapsulation, a coupled simulation approach combining the Boundary Element Method (BEM), the Finite Element Method (FEM) and the Poroelastic Finite Element Method (PEM) has been developed. This methodology has been already presented and validated through experimental measurements, demonstrating its acoustic effectiveness in the encapsulation of a generic electric motor housing. While BEM is well-suited for modeling exterior acoustic propagation, standard implementations encounter limitations at high frequencies due to mesh density requirements and computational cost. This work presents hybrid parallelization strategies that integrate frequency-domain decomposition with multi-threading to accelerate BEM H-matrix computations. Frequency decomposition enables parallel processing by distributing independent frequency tasks across multiple processes, while multi-threading enhances performance for fine-grained operations such as matrix assembly and H-matrix compression within each frequency. The processes and improvements enabled by these strategies are discussed and presented within an adapted high-performance computing (HPC) environment.
Sound source identification based on beamforming is widely used today as a spatial sound field visualization technology in wind tunnel experiments for vehicle development. However, the conventional beamforming technique has its inherent limitation, such as bad spatial resolution at the low frequency range, and limited system dynamic range. To improve the performance, three deconvolution methods CLEAN, CLEAN-SC and DAMAS were investigated and applied to identify wind noise sources on a production car in this paper. After analysis of vehicle exterior wind noise sources distribution, correlation analysis between identified exterior noise sources and interior noise were conducted to study their energy contribution to vehicle interior. The results show that the algorithm CLEAN-SC based on spatial source coherence shows the best capability to remove the sidelobes for the uncorrelated wind noise sources, while CLEAN and DAMAS, which are based on point spread functions have definite limitations. Considering the testing car, the main noise source of exterior is from the wheelhouse region, then follows the rearview mirror with much lower sound energy. However, noise from the mirror contributes most to the vehicle interior, while the contribution from wheelhouse region ranks the second place. In addition, windshield wipers and door handle can do perceptible contributions to vehicle interior noise at some characteristic frequency bands.
This study introduces a computational approach to evaluate potential noise issues arising from liftgate gaps and their contribution to cabin noise early in the design process. This computational approach uses an extensively-validated Lattice Boltzmann method (LBM) based computational fluid dynamics (CFD) solver to predict the transient flow field and exterior noise sources. Transmission of these noise sources through glass panels and seals were done by a well-validated statistical energy analysis (SEA) solver. Various sealing strategies were investigated to reduce interior noise levels attributed to these gaps, aiming to enhance wind noise performance. The findings emphasize the importance of integrating computational tools in the early design stages to mitigate wind noise issues and optimize sealing strategies effectively.
The influence of moisture adsorption, prior braking, and deceleration rate on the low-speed braking noise has been investigated, using copper-free disc pads on a passenger car. With increasing moisture adsorption time, decreasing severity of prior braking or increasing deceleration rate, the noise sound level increases for the air-borne exterior noise as well as for the structure-borne interior noise. The near-end stop noise and the zero-speed start-to-move noise show a good correlation. Also, a good correlation is found between the noise measured on a noise dynamometer and on a vehicle for the air-borne noise. All the variables need to be precisely controlled to achieve repeatable and reliable results for dynamometer and vehicle braking groan noise tests. It appears that the zero-speed start-to-move vehicle interior noise is caused by the pre-slip vibration of the brake: further research is needed.
To meet vehicle interior noise targets and expectations, components including those related to electric vehicles (EVs) can effectively be treated at the source with an encapsulation approach, preventing acoustic and vibration sources from propagating through multiple paths into the vehicle interior. Encapsulation can be especially useful when dealing with tonal noise sources in EVs which are common for electrical components. These treatments involve materials that block noise and vibration at its source but add weight and cost to vehicles – optimization and ensuring the material used is minimized but efficient in reducing noise everywhere where it is applied is critically important. Testing is important to confirm source levels and verify performance of some proposed configurations, but ideal encapsulation treatments are complex and cannot be efficiently achieved by trial-and-error testing. Simulation is a key supporting tool to guide location, thickness, and properties of encapsulation acoustic treatments to meet targets with no excess cost or weight. Effective simulation accounts for mass, damping, and acoustic attenuation effects of the encapsulation with fine detail in all propagation directions and in a wide frequency range that corresponds to what will most affect an occupant, generally up to 10kHz. This paper presents an approach coupling a Boundary Element Method (BEM) approach to a poro-elastic material (PEM), representation of the encapsulation that accounts for all mass, damping, and acoustic attenuation effects on a base component structure modeled classically by a Finite Element Method (FEM). The modeling methods are described and representative comparisons of bare and encapsulated acoustic transmission are shown. Application recommendations are given and next steps to advanced use of the method are presented, which is suitable to characterize sources attenuated by encapsulation that can be used to simulate vehicle interior and exterior noise.
This SAE Standard is equivalent to ISO Standard 362 - 1997 except for the differences detailed in Appendix A, and includes the modifications adopted by WP 29 in ECE R51 Revision 1 and EEC 92/97 and EEC 96/20. This document specifies an engineering method for measuring the noise emitted by accelerating highway vehicles of all types (except motorcycles) in intermediate gears with full utilization of the available engine power. The method is designed to meet the requirements of simplicity and reproducibility of results under realistic vehicle operating conditions. Measurements relate to operating conditions of the vehicle which give the highest noise level consistent with urban driving and which lead to reproducible noise emissions. Therefore, an acceleration test at full throttle from a stated engine or vehicle speed is specified. The test method calls for an acoustical environment which can only be obtained in an extensive open space. Such conditions can usually be provided for: a Measurements at the manufacturing stage b Measurements at official testing stations Measurements must be carried out in an acoustical environment which fulfill the requirements stated in this document. It should be noted that spot checking of vehicles chosen at random can rarely be made in an ideal acoustical environment. If measurements have to be carried out on the road in an acoustical environment which does not fulfill the requirements stated in this document, it should be recognized that the results obtained may deviate appreciably from the results obtained using the specified conditions. The results obtained by this method give an objective measure of the noise emitted under prescribed conditions of test. However, it is necessary to consider the fact that the subjective appraisal of the annoyance of different classes of motor vehicles is not simply related to the indications of a sound level meter. The motorcycles are covered in other SAE documents that prescribe an operating mode that is more representative of actual use.
Pass-by noise measurement is mandatory for automotive manufacturers for conformity of production. With evolving of pass-by noise requirements (under 68 dB in 2024), all the stakeholders should be able to comply with this criterion. OEMs, suppliers of passive acoustic treatments, road manufacturers and tire manufacturers are concerned and should deploy efforts to provide solutions for control of exterior noise. In this regard, simulations are preferable over measurement campaigns as they can provide fast feedback on passive exterior treatments for exterior noise control. In the particular case of Lightyear vehicles, the main contributors to pass-by noise are tires and in-wheel motors. Considering that, a contribution of each of these two sources of noise to pass-by noise will be described. Tire noise sources and motor noise sources will be replaced by simple monopole sources. The best monopole source location for both tires and motors is discussed. Actran vibro-acoustic Finite Element software is used to predict the noise at pass-by microphones. The calculation process takes advantage of advanced techniques to optimize the process. The acoustic transfer functions (TFs) from monopole sources to microphones are calculated first. The TFs are computed in different conditions considering acoustic treatments in different areas. Finally, these transfer functions are recombined with source strengths from tire and motor monopole sources. The pass-by noise simulation results are compared to the pass-by noise test results to conclude on the simulation accurateness.
Current and future EV’s contain significant amounts of complex electrical hardware, including rechargeable energy modules, control units, cooling systems and wiring situated inside the cabin usually below the carpet, seats or trunk trim and below the cabin floor. These items, whilst likely to have a direct impact on transmission loss, are increasingly difficult to evaluate via typical methods of computer-based simulation. In particular, the packaging space allocated for control units, which may require an air gap between the body in white and the carpet for aspects of heat stabilization can be difficult to model using the transfer matrix method. In the case of battery installations their high bulk mass doesn’t necessarily provide significant increases in transmission loss due to adjacent acoustic weaknesses and the inherent sensitivity of the floor system. This paper examines a selection of novel techniques, using sound Phonons, developed to predict both baseline transmission loss and absorption and subsequently acoustic performance optimization. The user-friendly nature of the sound Phonon application enabled “full vehicle” models to be efficiently created for interior and exterior noise prediction. This is particularly useful for EV target compliance evaluation when a platform is undergoing conversion from ICE to EV or assisting a “clean sheet” EV design.
Numerical methodologies for aeroacoustic analyses are increasingly crucial for car manufacturers to optimize the effectiveness of vehicle development. In the present work, a hybrid numerical tool based on the combination of a delayed detached-eddy simulation and a finite element model, which relies on the Lighthill’s acoustic analogy and the acoustic perturbation equations, is presented. The computational aeroacoustics is performed by the software OpenFOAM and Actran, concerning respectively the CFD and the FEM. The aeroacoustic behavior of the SUV Lamborghini Urus at a cruising speed of 140 km/h has been investigated. The main aerodynamic noise phenomena occurring in the side mirror region in a frequency range up to 5 kHz are discussed. The numerical simulations have been verified against the measurements performed in the aeroacoustic wind tunnel of the University of Stuttgart, operated by FKFS. The predicted exterior noise propagation into the far field has been validated by comparing the sound pressure level with the experimental data measured by exterior microphones, which were located outside the turbulent region beside the wake of the side mirror. Furthermore, the noise transmission into the cabin through the side window has been modeled. Simulation results have been validated by means of interior microphones installed on the driver seat. Both the exterior and the interior noise predictions show very good correlations with experiments. Lastly, a comprehensive investigation of the most critical aeroacoustic sources has been carried out. The numerical tool has been proven to be in good accordance with the microphone array with respect to the distribution of the sound pressure level in the proximity of the side mirror. Besides, the main vortex structures involved in the generation mechanisms of wind noise have been investigated by a CFD analysis. The entire CAA process has been proven to be accurate and suitable for combined analysis between the generation mechanisms of wind noise and the resulting transfer into the interior cabin to the driver’s ear as well.
The character and level of noise in a vehicle has changed significantly from the 1970s to today. In the 1970s the challenge was to permit communication from the front seat to the rear at highway speeds. In the last decade, the challenge has grown to provide a vehicle that provides the right "type" of sound while isolating the occupants from disturbing exterior noise. This may involve adding engine noise simulation and sculpting the interior sound to meet customer expectations. More recently, the challenge has been to modify noise controls for extreme light weighting exercises and electric vehicles. In addition, electric vehicles present a different sound environment and the challenge of determining what an EV should sound like. This paper will attempt to discuss these challenges and talk about the future of vehicle interior noise.
NVH is very important topic in development of a vehicle. Legislative requirements for driver ear level, the comparison to competitor vehicles in terms of noise and vibration as well as sound quality set very challenging targets. High noise at Driver Ear Level (DEL) and tactile vibrations of tractor is the major cause of exhaustion to the operator. With growing competition there is need for the tractor manufacturers to control noise and vibration levels. Recognizing the corrective measures to reduce the noise and vibration has a greater impact in increasing the efficiency of the product and operator comfort. Objective of this paper is to control vehicle level noise and vibrations using vehicle level structure modifications. It includes airborne and structure borne NVH study on a tractor by measuring sound pressure and vibration levels at vehicle level. Single cylinder engine was mounted on light weight structure to meet the power and torque requirements in the tractor. Also, there is no passive vibration control system in Indian tractors. Due to this the problem of noise and vibration arises. There is need to isolate the engine and transmission vibration from the body with rubber mounts. In this way appreciable reduction in noise and vibration can be achieved. Tests were performed to distinguish the root cause of unwanted noise and vibrations produced during operation of the tractor. Abnormality in exterior noise was observed. These problems were rectified by structural alterations. Addition of acoustic side shields and oil sump cladding was beneficial for exterior noise. Vibration was found higher at all tactile locations. Addition of frame stiffeners improved vibrations significantly at all tactile locations. Attachment point stiffness also increased. Addition of masses on steering wheel, driver seat locations.
NVH has gained importance in the field of earth moving equipment due to the demand of quieter machines and stringent in-cab as well as exterior noise emission norms. Several parts of the world have adopted strict legislation on noise emission by earth moving equipment, but many countries have not adopted any regulations till date. The aim of this study is to help governing bodies as well as machine manufacturers in adopting simple yet accurate testing method for compactor machine. The study consists of directivity analysis, noise source identification, noise source ranking and 4-point microphone position sound power evaluation method applied to compactors with wide range of engine power ratings. All the tests in 4-point method and directivity analysis were performed under stationary as well as dynamic conditions. Currently, several countries and vehicle manufacturers have adopted sound power evaluation of compactor exterior noise emission by 6-point method (as per ISO 6393 and ISO 6395) which consists of six microphone positions. The 4-point method presented in this paper tries to reduce measurement positions from 6 to 4, thereby simplifying the testing method, reduce instrumentation cost and measurement time. Results shows that the maximum error between the two methods was 0.7% in stationary condition and 0.6 % in dynamic condition. Directivity analysis shows that the compactor is extremely directive at its rear side and emitted maximum sound power at 180°. However, it is observed that microphone positions mentioned in ISO standards are not suitable enough to capture this noise which results in underestimation of exterior sound power level. Major noise source such as engine, cooling fan, hydraulic pump, air intake system were also analyzed. Air intake system was found out to be source of maximum noise in compactors.
The automotive industry is shifting towards the development of hybrid electric and electric vehicles. These vehicles primarily use electric motors for propulsion and can be significantly quieter to pedestrians than traditional ICE (internal combustion engine) vehicles. The NFB (National Federation of the Blind) and others highlighted a concern with these quiet vehicles related to pedestrian safety and the inability to use historical sound signatures to detect a moving vehicle. To address this concern, NHTSA created FMVSS 141, which identifies minimum external sound requirements for hybrid and electric vehicles during stationary conditions and in motion up to 30kph. [1] OEMs are now required to implement Acoustic Vehicle Alerting Systems (AVAS) that use external speakers to generate additional noise to meet the regulation. These noises are intended to raise the exterior sound level of the vehicles, while still attempting to maintain a quiet, pleasant experience for the passengers in the cabin. The purpose of this paper is to outline the process used by an OEM to develop a sound which meets the FMVSS requirement with consideration towards a pleasant experience for the vehicle occupants. A systematic development process was created and will be discussed throughout this paper that includes speaker location, speaker component testing, vehicle dynamic test considerations, vehicle acoustic sensitivity evaluation, sound design including jury testing, and final sound tuning. By following a structured approach, the authors of this paper believe an AVAS system can be developed to produce an external sound that is the best balance between a robust passing of the regulation while maintaining a quiet and pleasant experience in the vehicle cabin.
Pass-by/exterior noise of earth moving machines (EMM) and forestry machines is becoming a focus at early product development stages. ISO 6395 (2) or EC/2000/14 (1) standards defines exterior noise test procedure for EMM. However, these standards do not provide insights for diagnosing any noise issues which may arise. The analysis challenges are posed by the moving machine and acoustic sources with respect to the stationary hemisphere target microphone on the ground and changing operating condition of sources as function of time. There is need to develop a seamless methodology to identify acoustic sources, quantify respective source strengths and rank partial contributions from each source to the total target microphone response in order to overcome the aforementioned challenges. This paper demonstrates use of time and frequency domain Acoustic Source Quantification (ASQ) combined with time domain overall sound pressure level computation to mimic operational test conditions which provides the ability to demonstrate partial contribution of each acoustic source during simulated exterior noise test run. The work was performed on a four-wheel drive Loader (4WDL) machine. This analysis approach provides quantified insights for the design team for overall machine noise improvements. To increase the value of such a method in the early design stage, an acoustic simulation model of a machine is developed, and a response analysis is demonstrated using the computed ASQ based results. The model is planned to be exercised for “what if” improvements based on contribution analysis. The physical modifications developed based on test results are implemented and tested for their effectiveness.
Noise and vibration measurements were conducted on eight light vehicles ranging from small compact passenger cars to a large sport utility vehicle on and off shoulder rumble strips of two different designs to assess the input to a vehicle operator when the vehicle departed from the travel lane. The first design was a more conventional design, consisting of cylindrical indentions ground into the pavement at regular 30 cm intervals, and a continuous sinusoidal profile with a peak-to-peak length of 36 cm. Triaxial vibration measurements were made at six locations, including the steering wheel and column, the seat cushion and track, and the front and rear spindles. Interior noise was measured at six locations, one at the operator’s outward ear and five at the front seat passenger (three in the fore/aft locations of the seat and at outboard and inboard ear locations). In addition to the in/on vehicle measurements, pass-by noise levels were made. The measurements were performed at 97 km/h and 72 km/h. The primary purpose of the measurements was to develop a recommendation for a standard rumble strip evaluation procedure that could be implemented by transportation agencies to assure comparable results when considering rumble strip designs that produce minimal exterior noise while maintaining sufficient warning input to the vehicle operator. This research did reveal some markedly different results between the test vehicles in both interior noise and vibration as well as pass-by noise. In this paper, these results are presented, and initial draft test procedures are reviewed.
This SAE Recommended Practice establishes the test procedure, environment, and instrumentation for determining the maximum exterior sound level of highway motor trucks and truck tractors over 4540 kg gross vehicle weight rating (GVWR) with governed engines under stationary vehicle conditions. The basic procedure involves a full throttle engine acceleration and a closed throttle deceleration with the engine inertia as the load.
Axial cooling fans are commonly used in electric vehicles to cool batteries with high heating load. One drawback of the cooling fans is the high aeroacoustic noise level resulting from the fan blades and the obstacles facing the airflow. To create a comfortable cabin environment in the vehicle, and to reduce exterior noise emission, a low-noise installation design of the axial fan is required. The purpose of the study is to investigate efficient computational aeroacoustics (CAA) simulation processes to assist the cooling-fan installation design. In this paper we report the current progress of the investigation, where the narrow-band components of the fan noise is focused on. Two methods are used to compute the noise source. In the first method the source is computed from the flow field obtained using the unsteady Reynolds-averaged Navier-Stokes equations (unsteady RANS, or URANS) model. In the second method, the azimuthal modes of the flow field obtained using the steady RANS with the moving reference frame (MRF) model are treated as the “sound source”. The acoustic field generated by the sound source is calculated by solving the inhomogeneous Helmholtz equation. The simulation process based on both methods is applied to a benchmark case from the literature and the simulated results are compared with experimental data.
Current vehicle regulations demand for a challenging decrease in the overall exterior noise as a benefit for the health of citizens and road users. New limits have been implemented in UN R51.03 (based on ISO 362-1:2015) to reduce the emitted noise both at constant speed and in full load so as to cover most of the real urban driving conditions. In order to achieve those targets the carmakers have to refine the trim of their vehicles and an experimental approach can take place too late. This paper shows a method for the pass-by noise simulation exploiting the numerical transfer functions and a library of experimentally characterized sources with the aim to reduce the noise and find out a better tradeoff between costs and effectiveness of the modifications. Moreover a simple software tool for the treatment of the data and to ease the workflow has been created and used for the rank assessment of the different paths.
In the highly competitive global automotive market and with the taste of customer becoming more refined, the need to develop high quality products and achieve product excellence in all areas to obtain market leadership is critical. Buzz, squeak and rattle (BSR) is the automotive industry term for the audible engineering challenges faced by all vehicle and component engineers. Minimizing BSR is of paramount importance when designing vehicle components and whole vehicle assemblies. Focus on BSR issues for an automobile interior component design have rapidly increased due to customer’s expectation for high quality vehicles. Also, due to advances in the reduction of vehicle interior and exterior noise, engine mounts have recently been brought to the forefront to meet the vehicle interior sound level targets. Engine mounts serve two principal functions in a vehicle, vibration isolation and engine support. The objective of this paper to experimentally analyze the impact of conventional engine mount design on the rattle and whistling noise audible from the engine mounts when the vehicle is subjected to rough road conditions and pot holes at slow speed. The test methodology demonstrates how to simulate and co-relate the actual vehicle level noise on a BSR 4 poster test rig. A design change in mount stopper is proposed to abate the rattle noise from engine mounts considering the numerous variables involved and without affecting the critical NVH (Noise, Vibration and Harshness) and durability performance parameters. The level of noise reduction achieved is quantified through the substantial reduction in BSR demerit score which in turn reflects the improvement in perceived quality of the vehicle, increased customer satisfaction index and improved JD power (JDP) ratings
The ability to assess noise transmitted through seals to cabin interiors early in the design process is very important for automotive manufacturers. When a seal design is inadequate, the noise transmitted can dominate the interior noise, making the wind noise performance of the vehicle unacceptable. This can cause launch delays, increasing costs and risking loss of sales. Designing seals using conventional experimental processes is challenging, since the location and strength of flow noise sources are not known when the seal design is planned. Making changes to the seal system after the tooling stage is expensive for manufacturers as tooling and redesign costs can be considerable. Deliberate overdesign by adding multiple layers of seals in a wide range of locations also can reduce profit by unnecessarily raising part and manufacturing costs. Consequently, there is a strong motivation to use reliable computational capabilities to predict interior noise transmitted through seals early in the design process to address these challenges, designing seals right first time. The current study presents a computational process that can be used to predict interior noise transmitted through seals early in the design process. This computational approach uses a Lattice Boltzmann method (LBM) based computational fluid dynamics (CFD) solver to predict the transient flow field and exterior noise sources. A statistical energy analysis (SEA) solver was used to transmit noise from these sources into the cabin through glass panels and seals. Experiments were performed to quantify noise transmitted through glass panels, window seals and door seals, allowing validation of the computational predictions. Detailed flow analysis was performed to gain insight into the noise sources and the exterior loads on both the seals and glass panels. Accurate prediction of the seal noise and the insight provided by the flow analysis showed that this computational process can be used early in the vehicle development process to design efficient seals for improved wind noise performance.
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