Sound and Vibration Measurement Method development

In passenger cars, the rear audio speakers are typically installed in a horizontal panel behind the rear passenger seat called the parcel shelf. An automotive OEM needed help to study the low-frequency vibrational characteristics of the parcel shelf and to develop an objective metric that could be used at the design stage to minimize loudspeaker-induced buzz, squeak and rattle (BSR) noise. To understand the variations in performance across the industry, and to aid in the setting of component-level targets for future production, data was acquired on six different vehicles. Both operational (with loudspeaker) and artificial excitation data (with impact hammer) were acquired to characterize the modal and vibrational properties of the parcel shelf in each vehicle. The dynamic stiffness, natural frequencies, vibration mode shapes, and operational deflection shapes were determined from the measured data, and used to develop an objective metric for parcel shelf loudspeaker-induced BSR noise.

The blind community is concerned that vehicles are becoming too quiet and unsafe for sight-impaired pedestrians. To evaluate alternative test procedures for assessing the detectability of quiet vehicles by the blind community, we conducted a study in conjunction with the University of California, Davis. We performed a jury study at the National Federation of the Blind of California Conference, where blind volunteers from the conference participated. A combustion engine vehicle was converted into an electric vehicle and speakers were attached at each corner.

Schematic of the test setup

Example of vehicle passing blind jury participants 

The vehicle was driven past the volunteers three times under different conditions. The subject raised their hand when they heard the vehicle and the distances from the subject were noted. The results of this study indicate that the loss of normal combustion engine noises may significantly affect the ability of blind individuals to distinguish approaching vehicles and that a substitute sound generation mechanism may be required to reverse this risk.

> Investigation into the detection of a quiet vehicle by the blind community (conference paper)

An Asian commercial vehicle OEM needed to design an optimized acoustic treatment package for a commercial truck.

 

They approached us to get training in NVH testing methods and statistical energy analysis (SEA) modeling strategies. Working in cooperation with a CAE partner, we developed and implemented a test plan to decompose total noise inside the truck cabin into structure-borne and airborne contributions and developed cost and performance-optimized interior acoustic treatments.

 An engineer from the vehicle OEM was on-site with both our engineers and the CAE partner for the duration of the project, to be trained in the NVH test and SEA methods used. At the conclusion of the project, NVH results, SEA models and recommendations for acoustic package optimization were delivered to the customer.

> SEA Modeling and Validation of a Truck Cab for Sound Package Optimization (Conference paper)
> Optimization of the Sound Package of a Truck using Statistical Energy Analysis (Conference paper)

A North American automotive OEM wanted to develop an acoustic transmission loss (TL) test bench that would allow test of an entire exhaust system down to 20 Hz.

Using an Impedance Tube Type 4206 as a starting point, we designed and fabricated a very low frequency sound source with higher sound pressure level output to allow for testing of the entire exhaust system with good frequency response down to 20 Hz.. In addition, we developed and fabricated components required to connect the exhaust system to the standard 100 mm and 29 mm diameters of the Impedance Tube. We also made a pair of termination elements of sufficiently varied impedances to facilitate testing using the so-called 2-load termination method. As a part of the development process, the test system was validated using a simple expansion muffler as a test object. At the conclusion of testing the OEM was trained to operate the test stand, and is now able to perform TL measurements independently.

An automotive OEM requested development of a pass-by-noise decomposition and synthesis tool. Test and analysis methods were developed to estimate the vehicle-level pass-by performance from component level data, both from physical and/or analytical sources. The methods allow for the estimation of the overall vehicle-level pass-by noise along with the contributions to the total and dominant frequency content from each of the key noise sources. This information can be used in two distinctly different ways. First, the pass-by noise levels can be estimated for new component-level design alternatives, from either physical testing and/or analytical predictions. Second, a target pass-by noise level can be specified and the required acoustic performance for the dominant noise sources can be calculated.

> Vehicle Pass-by Noise Estimations for Component-Level Design (Conference paper)

An automotive OEM needed to optimize the acoustic package of its production truck and remove redundant stopgap fixes that had been applied pre- and post- launch to achieve the desired NVH performance.

The goals of the project were

• to optimize the released NVH package for improved cost and weight without degradation of NVH performance 
• to develop a practical, efficient, and reliable process to optimize NVH package development through integration of test and analytical tools. 

The goals were achieved by developing a synthesis process that allowed for the prediction of interior sound levels for alternative NVH package configurations. Acoustic contributions from the powertrain through specific paths into the interior of the cab were synthesized with and without modifications, making it possible to listen to different acoustic package scenarios and compute sound quality metrics, to identify the most cost-effective configuration.

 

> SEA Modeling and Validation of a Truck Cab for Sound Package Optimization (Conference paper)
> Optimization of the Sound Package of a Truck using Statistical Energy Analysis (Conference paper)

 

A vehicle OEM wanted to evaluate the sound quality (SQ) effect of an alternate powertrain in a production vehicle without having to actually swap the powertrain. We developed a new process that leveraged an experimental time-domain Source Path Contribution (SPC) model of the existing vehicle and powertrain. This allowed us to virtually swapping powertrains. Different engines could be virtually implemented into the SPC model and the results listened to and compared to established platform targets. The main objective of the project was to develop a test and data analysis process completely open to the OEM’s engineers to replace a supplier’s proprietary, frequency-based, method. The new process can be used to pre-empt severe sound quality concerns when integrating different/new powertrains into production vehicles. The project demonstrated that the SPC reconstruction of interior noise at steady state and run-ups in the tested vehicle with the ‘virtually’ swapped powertrain correlated well with measured data and therefore could be trusted to assess the SQ impact of a different powertrain in the same body.

Reference paper  

A vibration isolator material manufacturer needed assistance in the development of a test procedure for determining the transmissibility of their material samples. In order to accurately measure the transmissibility of a vibration isolator the isolator must be realistically loaded, as the material properties depend on the static loading of the sample. We developed a test setup to measure the transmissibility under various static loads. The transmission ratio (TR) curves were measured using a modally tuned impact hammer and accelerometer responses on the “’ground” ‘ and “’active” ‘ parts of the fixture assembly. The developed method proved to be a simple and accurate process for generating transmissibility curves for rubber isolator materials.

We were approached by a medical technology provider for help in modifying medical equipment alarm sounds for a formal jury test. In the jury test, the sounds must be heard as they would be heard in a realistic environment, and as if the listener were in specific positions within the room. The alarm sounds delivered by the customer were recorded independent of any ambient noise or environment, so the goal of this project was to synthesize sounds that are true to a realistic environment. Ambient noise recordings and impulse response (IR) functions were measured in a medical clinic facility. The ambient recordings were used to provide the “’background” ‘ in the synthesized sounds, where the IR functions were used to simulate the listener position within the room for each recording. The sounds were synthesized and used to develop a playback toolbox for the customer to use in the jury test.

A subsidiary of an automotive manufacturer of commercial vehicles and light trucks chose us to provide support and training for powertrain, full and trim body modal testing. Stationary vibration measurements were performed at the customer’s facility in China. Modal testing of components and multiple vehicle configurations were performed along with vehicle acoustic and tactile sensitivity measurements to assist in the customer’s CAE correlations. We trained the customer in experimental modal testing so the customer could move past just taking frequency response function data. In addition, the training allowed the customer to continue to support their CAE correlation activities after this project was completed.