**Author details**

In final stage, hand sketching is used to express the solution by means of the working principle. Sketching is a handy tool for the designer to visualize the working principle, product ideas, and parts quickly on paper. The sketches show how parts may be produced and assembled. However, implementing it in a product is often not feasible, therefore the intended sound cannot be measured. The toothbrush changes are based on sketching because making a prototype with rapid prototyping could bring you far away from the final solution because the replacement material has never the same sound property. In figure 9 sketches of a redesign

The two types of product sound need their own design process. Consequential sounds are the result of the product layout. However, the component choice, shape, material and manufac‐ turing are the main parameters that determine the consequential sound. For a new innovative product, sound recordings of different components will be made and mastered into a future product sound (Van Egmond, 2008). In this situation, the product sound will rely on the experience of the product sound designer . In future, this experience should be replaced by a theoretical framework based on research on the following parameters: material, accuracy of parts, the tolerance of parts, how the parts are connected, power transport, size, geometric,

Although consequential sounds are restricted in degrees of freedom by the design and embodiment of the product, the design of intentional sounds has an unlimited number of degrees of freedom due to the fact that they can be designed from scratch. This is one of the reasons that many feedback and alarm signals are badly designed, because no limiting constraints are imposed. If one considers the design of intentional sounds as a form of interaction design, the interaction can impose the constraints on the design of the sounds. Consequently, the sounds will "fit" their function better. Knowledge from interaction design, psychoacoustics, audio engineering and music perception will form the theoretical basis of the

It can be concluded that Product Sound Design should be a discipline within the domain design. Especially, the physical and psychological aspects should be mapped onto each other. The product sound designer has to learn from a variety of disciplines, from design to engi‐ neering and from acoustics to music perception. The course in product sound design is a good basis for further self-development of young designers. It enables opportunities for students under supervision of their lecturers to develop a systematic approach for product sound design. Hopefully, this will lead to more knowledge and appreciation of the way sound

are shown.

**7. Discussion and conclusion**

70 Advances in Industrial Design Engineering

speed, and assembly tolerances.

design of these sounds.

contributes to the overall product experience.

Lau Langeveld, René van Egmond, Reinier Jansen and Elif Özcan

Delft University of Technology, The Netherlands
