**1. Introduction**

Nowadays, consumer preferences are highly changeable, under a limited amount of resources, and it is difficult for a company to meet the demands of a variety of consumers of the stereo market. Being confronted with this condition, a company needs to consider a way of determining the most beneficial market for itself and to serve the consumers of that market in an efficient way. Due to the fact that typical design evaluation methods are not capable of correcting the evaluation of fuzzy messages from the aesthetic aspect, a new approach of assisting consumers in selecting stereo speakers by implementing the fuzzy theory has been developed. Lo et al. [1] proposed the use of the fuzzy breaking-circle method on the design of product interface operation and layout. Ko et al. [2] and Ko [3] proposed the analysis of the hot zones of users' product operability to carry out the re-arrangemen<sup>t</sup> of layout design for analysis.

Quantitative approaches were proposed by scholars such as Kwahk and Han [4], Lee et al. [5], Lee et al. [6], Heo et al. [7] and Jin and Ji [8] for carrying out the principles of usability evaluation respectively. In their studies, they introduced the usability risk level evaluation during the earlier stage of conceptual designs. This is due to the fact that a design at the earlier stage might a ffect the usability interface. Moreover, from the aspect of product designs, the decomposition and analysis of a product by perceptions and practical operations was proposed by Chou [9], Hsiao et al. [10] and Ko et al. [2] in order to determine the optimal solution.

Therefore, the goal of this study is to determine the appropriate design case study that can demonstrate the development of this type of research method. Considering the expected product attributes, the product to be reviewed in this study should be at the mature stage of its life cycle so that the design consideration focuses on the manufacturing and assembly stages. Stereo speakers serve as a good case study as they are mostly assembled by screws or latches in a similar way to other home appliances. The main approach is to use the morphological charts to classify various components in order to simplify a problem. An experiment was also carried out by showing the participants mechanical simulation videos of a product. The design ideas were presented in the form of 3D models by excluding the consideration of color and material. The aim of this study is to achieve the following goals:


#### **2. Materials and Methods**

#### *2.1. Introduction to Assembly Design*

In this section, the literature that is relevant to the assembly process of components of a product and its evaluation is reviewed.

#### 2.1.1. Planning of the Assembly Process

In order to carry out systematic planning and analysis of product assembly, various approaches of assembly planning and determining the ranking and principles of evaluations have been proposed by researchers. Depending on their methods or aspects, they are described respectively as follows:


In addition, there are also reviews of the approach of decomposing and depicting the structural diagram and the approach that uses matrices for analysis.

Barbosa and Carvalho [11] proposed a guidance of applying the concept of design for manufacturing and assembly (DFMA) to specific applications such as airplane design and manufacturing. Via the traditional design for assembly approach, Moultrie and Maier [12] proposed a new approach to encompass an original assessment tool and its delivery process. Their approach included custom designed post-it notes and simple check lists for scoring. Tiwari et al. [13] integrated design for manufacturing (DFM) and design for assembly (DFA) into information communication technologies (ICT) to establish a design for manufacturing and assembly/disassembly with the joint design of products and production systems in order to realize the target standard of Industry 4.0. Sossou et al. [14] proposed a process-independent, structured and systematic method for designing assembly-free mechanisms.

#### 2.1.2. Method of Evaluating Assembly

The relationship between a product's design and its assembly approach a ffects its cost. Approaches that have been used to evaluate assembly design in various industries are summarized as follows:

