A vehicle’s sound quality can have a direct impact on the driver’s perception of both the acceleration and dynamic driving performance—and in turn his or her overall satisfaction with a product. In response to this, automakers are investing painstaking effort to get the sound of a vehicle just right as a way to enhance customer opinion and differentiate it from the competition.
Perhaps the biggest challenge in the NVH development process is ensuring that all stakeholders in the development team are involved in sound-quality decision-making throughout the vehicle program. Sound targets need to be communicated to key program management and decision makers for them to be able to sign off on the targets and commit to any hardware required to deliver them.
Traditionally, achieving the targeted vehicle acceleration sound quality involved the creation and evaluation of multiple iterations of prototypes, making it a laborious and costly process. However, in recent years, NVH simulators have enabled a cost- and time-efficient method for capturing the opinions and decision-making processes of non-NVH experts.
Using an NVH simulator, engineers can understand the sound of vehicle components more thoroughly and simulate the target vehicle sound at their desk. Realistic countermeasures applied to the contributing components or changes to the components themselves can be simulated to create and demonstrate the targeted acceleration sound, reducing the number of iterations with prototype parts and giving the vehicle product planners the ability to evaluate the targeted vehicle sound within an interactive and realistic driving environment. Furthermore, the value of each treatment can be assessed from the customer perspective by the program team and compared with the cost of its implementation.
Brüel & Kjær offers several NVH vehicle simulator systems. For use in the R&D office, B&K’s Desktop NVH Simulator, developed to meet a Jaguar request, uses driver controls—accelerator, gear, steering, and brake—as inputs to a real-time sound model that accurately re-creates the sound of a car over its full driving envelope. It displays a sufficiently realistic visual scenario on a series of computer monitors so that experts and nonexperts can assess the sound quality of existing or virtual vehicles with confidence while driving.
“It was based on the need for having a more consistent way of evaluating and communicating the NVH performance of a vehicle before you have an actual physical prototype,” said Torben G. Nielsen, Business Manager–Automotive, Brüel & Kjær. “It is late in the game to have decision makers drive a prototype and say, ‘No, this is not really what I want,’ even if the specs in terms of raw measurement results are still OK, but the feel or the subjective evaluation is not acceptable for the decision maker.”
B&K’s Full-vehicle NVH Simulator is a project-based solution where a vehicle, with vibration applied at the driver contact points, is placed in front of a projection screen where a virtual scenario is projected, and an assessor experiences the sounds and vibration of whichever vehicle model is selected in the software while virtually driving through a planned environment. The simulator responds to the driver’s input and reproduces the correct sound and vibration for the instantaneous scenario.
The recently introduced On-road Vehicle NVH Simulator (ORS) takes the evaluation out of the test lab and enables edited and modified vehicle sounds to be listened to, evaluated, and compared while driving a vehicle on an actual road and on a variety of surfaces.
“The on-road simulator offers a possibility of taking the desktop simulator on the road, so you can bring the laptop to the car and then instead of, as you do in the desktop simulator, where you sit with a PC steering wheel and gas pedal and gearstick and so on, you actually use the steering wheel, gas pedal, etc. on the car,” Nielsen said.
With the ORS, developed for a project with Nissan Technical Center Europe, the instantaneous measured performance of the vehicle as it is being driven (rpm, speed, load, gear) replaces the real-time empirical performance model used in the desktop simulator. All of the mixing and filtering capabilities of the desktop version are active in the ORS, so target harmonics can be modified or switched on or off in real time while driving on the road.
The sounds are played through aurally transparent open-backed headphones. “You need high-quality open headphones because the overall success criteria is that people feel that this is very, very realistic,” Nielsen said.
Prior to playback in a simulator, competitor and donor vehicle sounds, on which the target sounds will be based, must first be recorded and simulator vehicle models created, although the simulator can use NVH data from any source, including CAE. Sounds may be recorded on a test track or on a normal road. For benchmarking purposes, data can be gathered quickly using B&K’s PDA-based SoNoScout recording and analysis system.
“You have your targets on the desktop simulator, and when you’re happy with those targets, you can implement them in a car that is close to what you want to make—maybe your competitor’s car or an existing car with some easily modified attributes,” said Gijs Dirks, Application Specialist, Brüel & Kjær Sound & Vibration A/S. “And then in the car as we drive, we synchronize the ORS model with the engine, using the driver controls and instantaneous RPM, so that we can use the ORS output on the headphones to modify the sound of the real car, which is heard through the headphones, into the target sound, which is what we want.”
For the NVH engineer, the DTS and ORS provide quick and easy tools that allow rapid, virtual prototyping of target sounds and NVH data from component designs to be evaluated in the lab and on the road. The modification tools also allow the data to be fine-tuned in real time while evaluating in the lab or on the road.
“It is a very valuable validation that people can drive a car and can be presented the sound that the target vehicle is going to have. Using these and other B&K tools, the target sound can be directly compared to the donor vehicle and cascaded to component level. This gives direction to the detail component engineering needed to implement the target sound quality,” Dirks said.
Matt Monaghan wrote this article based on SAE Technical Paper 2009-01-2178 by David Quinn and Paul Speed-Andrews, Nissan Technical Center Europe, and Mark Allman-Ward and Thorsten Heinz, NoViSim Ltd; and SAE Technical Paper 2009-01-2190 by Farokh Kavarana, Gene Taschuk, and Todd Schiller, Nissan Technical Center North America, and David Bogema, Brüel & Kjær North America.