Sound Check

Making a vehicle sound good takes more than a good ear and lots of prototypes.

“In this business, you’re not only judged by how much noise you make, but how it sounds to the customer,” says W. Jay Poole, director, Product Engineering, Tenneco (Lake Forest, IL; www.tenneco.com). Getting to that special sound used to take lots of experience, and almost as much trial-and-error testing of prototype exhaust systems, but those days are over. By using Gamma Technologies’ (Westmont, IL) GT-Power one-dimensional engine simulation and gas analysis software, it’s possible for Tenneco engineers to model the desired exhaust sound based on available parameters, and provide a number of options for the OEM to choose from. Tenneco modeled 200 mufflers for the Harley-Davidson version of Ford’s F150 in software, but only built 15 for actual testing.

After modeling the candidates, Tenneco engineers were able to bring program members into a sound-proof room and play the sounds over the computer. With each participant listening through a pair of stereo headphones and given a sheet on which to rank the sounds, it was possible to winnow them down, compare them, and choose the finalists. Once the prototypes were built and tested, it was possible to hear the actual units on the road and compare them to the virtual muffler. As Brent Bauer, senior v.p. and general manager, Tenneco North American Original Equipment Emissions Control, put it: “You can’t just make it loud and call it ‘sporty’ anymore.” Tenneco, he observes, is being asked to help the Japanese OEMs develop exhaust systems for their special-edition light-duty trucks, the first of which launches in 2007.

Tenneco upgraded its Grass Lake, MI, engineering center to meet growing demand for OEM and aftermarket demand for exhaust and emission systems technology. It added 30,000 ft2 to the facility to make room for a raft of new equipment, including a state-of-the-art all-wheel-drive hemi-anechoic chamber that can handle vehicles with wheelbases from 80-in. to 185-in., and dyno speeds as high as 140 mph. DynaMotive (Leicestershire, UK; www.dynamotive.co.uk) built and services the test chamber, whose 6-foot rolls weigh 12,000-lb each and can split torque between the wheels. Tenneco can do in- and out-of-phase testing on this unit, as well as cobblestone NVH testing by making molds and placing them on the rollers.

Four new engine dyno test cells were also added, and these are isolated from the rest of the building. Not only is the building HVAC isolated in each test cell, the walls around them are sand-filled to further reduce noise and vibration transmission throughout the facility. The cells can be run in shifts around the clock if necessary. To round out the improvements, Tenneco also upgraded the facility’s cold air flow, sound quality room, and added a heavy-duty truck hoist and lab area. These improvements build on the equipment currently in the facility, which includes a MTS 323 Mast system with 6? of freedom of motion with up to three auxiliary control channels to test complete exhaust systems on the vehicle, electro-mechanical shakers large enough to handle heavy-duty trucks (only NASA and Lockheed Martin have larger shakers), and a material analysis lab. “As global regulations and quality pressures increase,” says Bauer, “we have to invest to keep ahead of the curve.”