Sound quality evaluation of drum type washing machine at drying and the improvement instance

In this study, we considered how to evaluate the sound quality of drum type washing machines. Firstly, a questionaire, that asked users to select appropriate terms for evaluating the sound quality, was carried out. A few terms were chosen frequently as the appropriate terms such as "discomfort." Subsequently, subjective evaluaton test using radiated noise of the washing machine at the drying was performed to obtain the most suitable evaluation term. The result indicated "noisiness" is the most common term among users, and the term was held common sense. We, therfore, set the term as the representative evaluation term for evaluating the sound quality. Subsequently, the loudness, that was calculated from the mesasured noise signal according to ISO 532B, expressed the noisiness level very accurately. Finally, we actually evaluated the noisiness of a drum type washing machine using loudness. Through the loudness analysis in each frequency band by Bark scale, the loudness at low frequency was highest influence on the overall loudness. Then, the low frequency noise was reduced by applying a countermeasure to the sound source part. As the result, not only the noise level but also the sound quality could be improved very much.