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Sounding off on vehicle acoustics


May 27, 2010
by Colin Novak

Sound quality is important when assessing the quality of a vehicle.

Photo: iStockphoto

Automotive manufacturers have made great efforts to improve the performance and reliability of cars over the past 20 years and as a result, consumers are more aware of other characteristics such as noise, but it’s the quality of the noise that may attract or repel a customer from a purchase.

The goal should be to improve the quality of the sounds produced by the automobile, which falls within a research area called sound quality or psychoacoustics.

Many factors affect the evaluation of sound quality. Traditional objective measuring and analysis techniques such as A-weighted sound pressure and frequency analysis are good at quantifying noise emission levels, but they fall short analyzing sound quality. Jury-testing techniques and purpose designed psychoacoustic metrics are key because ultimately only the human ear can tell product engineers and developers whether a product has the right sound.

With the help of the AUTO21 Network Centres of Excellence, the Noise Vibration Harshness and Sound Quality (NVH-SQ) research lab at the University of Windsor in Windsor, Ont. is determining sound quality properties associated with the use of magnesium as a structural component in automobiles. The goal is to minimize the use of sound absorbing materials, which would negate the weight advantage of the magnesium.

Magnesium’s lower weight would contribute to improved fuel economy while maintaining structural strength but there would be more noise transfer throughout the vehicle. Researchers use several sound quality metrics and then optimize the use of the magnesium to derive the best acoustic properties.

Sound quality research is also investigating a new type of police siren that emits a low frequency modulating sound with the conventional high frequency wailing siren.

Modern vehicles are better designed to isolate the interior of a vehicle from exterior sounds such as road noise, but it impairs the driver’s ability to hear high frequency emergency sirens.

Gauging driver reaction
A low frequency modulation penetrates the soundproofing but researchers want to determine to what degree it grabs the attention of a driver without being startling. To accomplish this, a Bruel & Kjaer NVH driving simulator is being used to gauge a driver’s reaction to an approaching police vehicle. Like a real car, the simulator has a steering wheel, foot pedals and three very large screens that project the roadway in front of the driver, including signs and other traffic. While listening through headphones, the driver hears a realistic representation of the car’s sounds and the approaching police car.