Trends in Vehicle NVH Testing

Before the era of air conditioning, everyone drove around in their cars with their windows rolled down for the fresh air. With the wind whistling through your hair, a quiet cabin environment was something of an unattainable goal, so drivers didn’t expect much from their new vehicles in terms of low cabin sound levels.

With the introduction of air conditioning in the 1939 Packard, cars could now be driven with the windows rolled up for all four seasons of the year and cabin noise levels became a much greater customer expectation. Mind you, the average vehicle from back then was still pretty noisy compared to even the least expensive car you can buy today.

The modern efforts to make large gains in cabin noise level reductions really took off in the early 90’s. Many automotive manufacturers experimented with duplicating cabin vibration environments using partial body bucks mounted on large shakers equipped with equally large head expanders. Early buzz, squeak and rattle (BSR) tests were run at high acceleration level to simulate worst-case conditions. While this approach was to yield many of the early improvements in cabin noise reduction, the high capital cost of such large shakers and cost of body bucks, made these early experiments expensive. With the reduction new platform delivery, body bucks are not normally available to an engineer who needs to perform a BSR test on their new center console design.

Today we use a lightweight structurally optimized fixture to simulate the vehicle body structure. In addition to being sufficiently rigid, this type of fixture is also optimized for low noise output. It’s important that noise produced by the DUT not be masked by noises produced by the test setup. To this end, modern BSR testing is conducted with relatively low force shakers at low g levels.

A modern BSR test setup can routinely achieve < 30 dBA, 1.2 Sone (N10 Zwicker Loudness) while under full test conditions. This much quieter than the very best vehicle cabins can achieve today. This is likely to change, though electric vehicles are raising the bar on cabin comfort and increasing the need for interior system BSR testing.

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