Crank rumble is an amplitude-modulation of engine noise perceived inside a car. It is common under full load acceleration but not under part load acceleration, so could cause concern.
Honda and Ricardo carried out a program of work to research methods to reduce the perceived (subjective) level of crank rumble inside a vehicle under part load acceleration.
Transfer Path Analysis (TPA) is a method of predicting vehicle interior noise by separating sources (the engine) and transfer paths (the vehicle body). TPA was applied in the time domain to allow subjective assessment of the different contributors to the interior sound quality. Subjective assessment was performed by a panel of listeners, to avoid bias caused by individual opinions. This approach identified key contributors to the perceived crank rumble, and allowed targets to be set.
Computer Aided Engineering (CAE) was used to study a range of modifications to the engine. The effects of the modifications were assessed subjectively, using TPA, relative to the vehicle level subjective target. Technology to allow this kind of assessment has not been available previously. Results were subsequently confirmed by testing prototype parts, using the same assessment method. An optimised package of countermeasures achieved a significant subjective reduction in perceived crank rumble.