In this paper a preliminary case study on the sound quality of power window regulators is presented, part of a broader project on the design of this component. In particular an experimental investigation is described in which different configurations, in terms of motor type, presence or not of silent blocks, motor supply voltage, were tested to select the most pleasant solution. For this purpose, psychoacoustic methodologies were considered and compared to other kind of approaches. Moreover two experimental set-ups were considered and their results compared: one with the component fixed to a car door and the other in a free-free configuration. The SPL (Sound Pressure Level) (dBA) time function appeared highly related to supply voltage, motor type and silent block insertion. Psychoacoustic parameters such as loudness and loudness percentile N5 were in good agreement with classical parameters (i.e. RMS, mean SPL (dBA)) providing additional information on sound characteristics. PA and time varying loudness maximum value seemed able to highlight further peculiarities of sound timbre. However they appeared controversially related in different experimental sessions, suggesting a sensitivity study in order to define standard test conditions (e.g. environment, assembling and measurement system) and remarking the importance of preliminary quality checks and repeated acquisitions to increase the statistical significance. Other parameters such as Kurtosis, percentile N90, sharpness, roughness, fluctuation strength gave uncertain indications and were not able to discriminate between different set-ups and their sound characteristics, probably due to their marginal value in this particular application and product. Motor rotational speed variation parameters gave different indications as regards the best set-up with respect to the psychoacoustic indices. In our case, in fact, voltage appeared to have opposite effects on such parameters and, since low values of loudness, sharpness and motor speed variations are often associated to overall product high quality, an optimum solution appears difficult to find without suitably combining and weighting the different parameters. This operation, in order to be successful, must be done tuning the model with or according to the client's sensitivity. Moreover, as shown by the tests on the single component compared to those on the door assembly, the results can differ a lot due to the acoustic effect of the door panel and masking phenomena. Therefore simulation on a computational modal and acoustic model of the component, validated by testing, and simulation on the assembly are essential for classifying the acoustic behavior of the component. Equally important is a jury test (with a jury carefully selected for the client's target) to confirm the significance of the chosen acoustic and psychoacoustic parameters for power window sound quality assessment. Such activities are under way.
A psychoacoustic approach for sound quality assessment of automotive power windows
2012
15 Seiten, 5 Bilder, 2 Tabellen, 22 Quellen
Conference paper
English
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