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This paper presents a new concept concerning engine mountings that can reduce engine booming noise by utilizing an additional vector. Booming noise in passenger cars, particularly those with a four-cylinder engine, is caused by exciting forces such as the second harmonic of engine intertial force. We have found that exciting forces transmitted from the engine to the body structure through the engine mountings are reduced by adding another vector which cancels out these exciting forces. This new vector can be obtained by using a mass-controlled region of a vibrating system possessing either a single degree or two degrees of freedom. When this optimally designed mechanism is adopted on a small passenger car, booming noise can be significantly reduced.