What is sound quality evaluation?

In these days, mechanical products, such as home appliances (air conditioners, refrigerators etc.), office equipment (copiers etc.), and automobiles, have come to be demanded comfort by reducing noise, while pursuing basic performance.
Conventionally, the noise from the equipment has been evaluated by physical quantity such as sound pressure level and acoustic power.
But because the final judgment of the noise is entrusted to human hearing, in evaluating, the psychological acoustic evaluation quantity which is related to the physical quantity has come to be used. The psychological acoustic evaluation quantity quantifies how a human being feels when hear it, and easy to obtain clues to know how to improve the sound quality from the sound quality evaluation amount. The method to feed back to the design of the equipment by using psychological acoustic technology is called acoustic design.