Autos: The Thunking Man's Car

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A small car glided out of an American Motors plant in Kenosha, Wis., drove quietly into the night and braked to a stop in a farm field. There, where the air was clear and city noise was absent, the passengers alighted and began loudly slamming the car's doors. After each slam, the men placed stethoscopes against the car body and listened to the lingering vibrations. Half an hour later, everyone climbed back into the car and returned to the plant.

This midnight ride of American Motors engineers was a regular test in their effort to develop doors that slam with what automen call a solid "thunk." One result showed up last week as American Motors introduced the Hornet, its new small car, with an advertisement that urged: "Open a door and listen for the reassuring thunk you get when you close it." In auto showrooms, the sound of a car door slamming touches some responsive chord in the frazzled psyche of the American buyer—and all the automakers know it. "There is very little to go on when you buy a car these days," says Carl Hedeen, General Motors' chief of body engineering. "If the glove box opens, the seats are soft and the doors thunk, that's all you have over the competition."

Angry Wife. Every year U.S. automakers invest millions of dollars and countless man-hours to produce the thunk that sells. G.M. employs 250 technicians—including graduates of Purdue,

Stanford and Michigan State—to work exclusively on doors. Ford, Chrysler and G.M. test and refine their thunks in soundproof chambers that are sealed like bank vaults. Stereo tapes are used to record the effects that subtle design changes have on the sound. High-speed movies are made to study vibrations, and oscilloscopes gauge the thunk's duration. The automakers also employ automatic slamming machines, which create sounds ranging from what G.M.'s Hedeen calls the "angry-wife slam" to the "husband-coming-home-late-at-night slam." The former is 50 foot-pounds, and the latter three foot-pounds.

Company chiefs like to test the thunks themselves. Chrysler Chairman Lynn Townsend sometimes drives subordinates to distraction by slamming doors repeatedly in the ear-splitting confines of a testing garage. American Motors Chairman Roy Chapin likes to go into his company's executive parking area to try out the thunk. Ford has a jury of product-development specialists to pass judgment on thunks.

The quality of the thunk depends on many factors: the rigidity of the car's body, the locks, the soundproofing in the door, the carpet on the floor. Heavier cars tend to have sturdier thunks, but lighter models can do well if aided by a few gimmicks. Special bracing inside the. door can improve the thunk, but technicians do not know just how or why. "There's a lot of black magic in this thing," says John Adamson, an American Motors' vice president.