DETROIT - Noise issues hit Siemens Automotive Corp. whenever it tries to boost the use of plastics under the hood.
While plastic parts offer automakers an easier and less expensive way to assemble working parts, they are noisier than metal parts, said David Geran, Siemens director of business development.
Lightweight plastics cannot absorb noise like metal, and Siemens cannot simply cover up the sound. Siemens' air-intake module brings in air from outside the vehicle, providing the oxygen necessary for the spark in the internal-combustion engine.
So instead, the company designs hollow resonators within the manifold, a reedlike opening that can eliminate an unwanted rumble in an engine's roar by altering the way air flows through the piece, much the way sound changes pitch when you blow across the opening of an empty bottle, Geran said.
'You can use the resonator to tune the sound of the engine,' he said. Not every car is going to sound the same, though, because the acoustics are tied to a vehicle's cost. If 5 percent to 10 percent of a car's production price goes to the sound design program, then there is more money to put into absorbers in a luxury car than in an economy hatchback. A typical luxury car could use 12 resonators in the manifold system, at a cost of $10 each, Geran said.
Siemens is researching ways to use electronics to replace the molded resonators. The electrical filters would work similarly, but automakers could manipulate the sound more, creating a sound design for each brand they produce, much the way motorcycle maker Harley-Davidson markets the sound of its bikes, Geran said.
'You can't make a (Ford Motor Co.) Focus sound like a tank, but you can give a Ford Focus its own sound,' he said. 'It won't sound like a Ferrari, but it will be its own sound.'
For a globally marketed vehicle such as the Focus, he said, the automaker could design an engine in Europe, where it is sold as a family sedan, then pep up the sound on vehicles sold in the United States, where it is targeted at first-time car buyers.
'You can support a marketing strategy,' he said.