The design of the converter has a considerable influence on exhaust emissions as well as engine performance and exhaust acoustics. Converters have an effect not just on the tailpipe noise but also on surface sound radiation of the exhaust system. The contribution of tailpipe and surface to noise emission of exhaust systems is for high performance engines in many cases approximately the same. The surface radiation affects not just the exterior noise of the vehicle but also the interior noise. The subjective noise as well as the objective noise is also influenced. Surface sound radiation therefore becomes increasingly more significant. This contribution will present results about the influence of the shape of the monoliths and the effect of different monolith mounting systems. The influence of thermal insulation and main shell design is also shown. The surface sound radiation of ceramic monoliths and metallic supports will be compared. In addition, we shall also see the effect of a converter on the tailpipe noise.