Ever stricter legislation is compelling vehicle manufacturers to reduce external vehicle noise. There is, for example, a recommendation before the European Commission that vehicle drive-by noise be reduced to 74 dB(A) for cars and light trucks to take effect from October 1994. Engine manufacturers are therefore exposed to an increasing demand to produce quieter products. This paper explains how certain companies are employing the Spatial Transformation of Sound Fields (STSF) technique to address this problem. A brief introduction to the main principles of STSF is given followed by a number of practical examples of measurements on engines in test cells.