| Summary: | Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. === Noise, Vibrations and Harshness (NVH) characteristics are becoming ever more significant in
today’s vehicle manufacturing industry. Similar to good vibration and harshness characteristics,
the perception of a vehicle’s quality is enhanced by a well sounding vehicle interior.
This study’s main aim was to develop objective equations to directly optimise interior sound
quality of light commercial vehicles ( ½ ton LCVs) on the South African market. The effects the
noise of the engine, the wind and road/tyre interaction during steady-state conditions have on
the interior sound quality of eleven comparable vehicles was investigated with the aid of a
binaural head. Steady-state condition in this content refers to the fact that vehicles were tested at
constant speeds, no acceleration involved. A strong emphasis was laid on the influence road
noise has on the interior sound quality of LCVs.
Other objectives for the thesis were, to provide a method to benchmark the interior SQ of LCVs
and to develop target values for objective metrics for these vehicles. Establishing a
comprehensive literature survey formed another objective of this study. It seeks to provide a
summary of the modern SQ analysis procedure and the findings of a number of studies. The
survey also presents an opportunity to compare this thesis’s results with previous studies. A last
objective was to develop a list of possible hardware modifications that would improve the
vehicle interior sound quality, influenced by different noise sources.
A strong correlation between vehicle and engine speed and Zwicker loudness as well as Aure
sharpness was found, for all test conditions. The road surface roughness was observed to also
have a strong influence on the objective metrics of vehicle interior SQ. Loudness was found to
be around 25% higher and sharpness around 5.6% lower in vehicles driving on rough tar roads
than on smooth roads.
Good correlations between a newly developed metric (the SPF), an equation in Zwicker
loudness and Aure sharpness, and subjective ratings was obtained for a number of test
conditions. Four objective equations, as well as target values for loudness and sharpness have
been developed to objectively optimise the sound quality of LCVs. Benchmarking interior
sound quality utilising the developed equations, will ensure continuous improvements in the SQ
sector for future LCVs.
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