Krause, P., Weltens, H., and Hutchins, S., "Advanced Design of Automotive Exhaust Silencer Systems," SAE Technical Paper 922088, 1992, doi:10.4271/922088.
This paper presents some of the innovative exhaust noise reduction techniques an exhaust system development engineer can employ, when his customer, the car manufacturer, increases the engine swept volume and engine power without allowing any change in the layout of the exhaust system, which may already be on the borderline from the acoustic point of view.The solution to this problem could be an “electronic” muffler. Here there are two possibilities: 1. A semiactive muffler, which will change the internal geometry of the muffler system or muffler in accordance with changes of engine conditions during driving. 2. An active system, which adds antinoise or modulates the pulsating exhaust gas flow in order to smooth the gas pressure pulsation and to get in this way a sound attenuation. The possibilities and limits of both solutions are shown by different measurement results.