Dynamics & Vibration Research Group

This research project is aimed at predicting and understanding the physics of in-vehicle noise with particular emphasis on boom noise. Boom noise is the result of the limited effectiveness of soundproofing or damping material to damp out the first few vibration modes of relatively small enclosures such as passenger car compartments. The interaction between the structural and acoustic modes in the low to mid-frequency range (40-200 Hz) creates a resonance behaviour. The average person may perceive this resonance as a low tone rumbling noise that may cause some hearing discomfort. Graphically, boom noise is recognisable by broad peaks that are a couple of decibels higher than the mean noise level. This is shown experimentally in figure 1(a). Figure 1(b) shows a plot of acoustic response with similar boom noise characteristics for a simple box-plate system. The motivation for this work stems from the fact that noise, vibration and harshness (NVH) levels are critical selling factors for car manufacturers. Thus the need to understand the nature of noise generation and transmission remains a prime objective in order to satisfy customer demands for increasing vehicle noise and vibration refinement. This research work is aimed at using simple models to simulate vehicle interior noise with its boom noise characteristic intact and comparing it with industrial data and experimental work. It is hoped that this will provide some insight into the problem that may lead towards a possible solution in future car design.



Figure 1: (a) Noise level transfer function measurements in various identical vehicles[1] (b) Simulated model for a box-plate system

Project Details

It has been mentioned that this study is proposed to understand the physics of boom noise using simple models. A trident approach of analytical theory, computation (MATLAB) and experimental studies form the core of this work.

A simplified model of a passenger car interior based on an acoustic cavity such as a box is proposed. Basically, the walls of this box would be rigid except on one or two sides where a flexible membrane or panel would be employed. A coupled structural-acoustic mathematical model would be formulated to study the frequency response of the cavity when subjected to external perturbations and structural irregularities such as having lumped masses. Due to the nature of boom noise that occur at relatively lower frequencies, a modified Statistical Energy Analysis (SEA) will be applied to formulate a theory to further describe the problem. Sensitivity-studies are also carried out. The last aspect of this work includes an experiment where appropriate measurements are made and compared with theoretical predictions, industrial data and published papers. The nature of the work in a nutshell is illustrated in figure (2).



Figure 2: Research work make-up

In addition to the abovementioned work, a review of the relevant literature is presented. Various (NVH) models including finite element analysis (FEA), SEA and experimental studies are reviewed. Also, a review of fluid-structure interaction work that can be related to vehicle interior modelling is discussed.

Relevant/Recent Publications

1. Rashid R., "Modelling and Analysis of In-Vehicle Boom Noise", First Year Report, CUED, (2002)
2. Cornish R. "A Novel Approach to Optimising and Stabilising Interior Noise Quality in Vehicles", J. Automobile Engineering, 214, (D7): 685-692, (2000)

Principal Investigator & Researchers

• Professor R. S. Langley
• Professor J. Woodhouse
• Raslan Rashid

Funding Bodies

• duration of funding: 2002-2004
• Institute of Strategic and International Studies (ISIS), Malaysia