**1. Introduction**

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sing design meetings: CRC Press; 2009. p213-29.

46 Advances in Industrial Design Engineering

In our daily life we are immersed in sounds that are generated by products. If one were to ask someone to name sounds produced by products, often sounds are mentioned that alarm or inform us (e.g., microwave oven beeps, telephone rings etc.). These are the sounds of which we are consciously aware. However, many sounds subconsciously play an important role in our interaction with a product. One hears if the battery of a toothbrush runs out of power; one hears the power of a vacuum cleaner and one hears if the bag is full; etc. Although these are all functional aspects, sound also plays a role in our aesthetic, quality, and emotional experi‐ ence of products. For example, one hears if the sound of a car door evokes a sense of quality. Car manufacturers have acoustical engineers to make sure that a slammed door will evoke this sense of quality. Sound quality and its relation to perception have been studied to some extent (e.g., Blauert & Jekosch, 1997; Bodden, 2000; Lyon, 2003). Often, these methodologies cover only one aspect of the design or evaluative process. Here we present a systematic approach to the inclusion of sound in the design process and its use as an essential aspect of controlling the quality of design and as a means of educating designers (and students) about the constit‐ uent parts of a product.

In this chapter, we will distinguish between sounds that are generated by the operating of the product itself and sounds that we intentionally add to a product. In the field of product sounds the first category has been named consequential sounds and the second category has been named intentional sounds (Van Egmond, 2007). This distinction is essential - both categories of sounds will require different design methods and the use of knowledge of different disciplines is needed. Intentional sounds are mostly composed which may be experienced as musical sounds. One could state that the use of intentional sounds as feedback of alarm sounds

© 2013 Langeveld et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Langeveld et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Langeveld et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

is in fact creating a small musical composition (i.e., musical motives). Therefore, these sounds can also be used to convey brand values of companies.

**2. Products**

**2.1. Technology**

energy loss.

A product is the result of a design process that starts with a design problem, involves ideation phases, and ultimately leads to a market introduction. In the context of product sound design, mainly domestic appliances are considered. The appliances have moving parts that can move linear or radial and are joined together in such a way to fulfills its functional aspect. and in particular the sound of the product. The product sound is influenced by many physical

Product Sound Design: Intentional and Consequential Sounds

http://dx.doi.org/10.5772/55274

49

Energy facilities are dependent on the place of use. For instance a product with a combustion engine is not used in houses or factory halls, because the pollution of the environment and sound intensity. Electricity is the most convenient energy type which is available in the form of batteries and power outlet. All other types of energy such as, hydro-electric power, fuel cells, human power, solar energy and atomic energy are not considered because the main power source is electricity. Electricity is easy to convert into another type of energy such as: thermo energy, mechanical energy, chemical energy, etc., but every conversion means an

Product sounds manifest themselves in mainly three sources airborne sound, liquid sound and structure-borne sound. In a product we are dealing mainly with structure-borne sound sources that find their way to the outside environment by radiation. Transfer paths take care of the propagation of the sound from the source to the environment of the product. Structure-borne sound demonstrates itself in solids, in constructions that are built up from plates, beams, shells and shafts. The material properties determine the propagation speed, which is constant for certain waves and forms. The propagation speed depends on elasticity, specific gravity and contraction, which is different for solid materials. However, steel and aluminium have the same propagation speed because the division of the elasticity by the density is the same (E/ρ).

**Medium Prolongation speed in m/s**

Air 340 Water 1500 Steel, Aluminium 5200 Iron 5200 Brass 3700 Glass (window) 6800 Wood (parallel) ρ=0.5 kg/dm<sup>3</sup> 4000 Lucite (Plexiglas) 2650 Polystyrene 2300 Rubber (soft) 50

**Table 1.** Propagation speed for a number of materials, liquid, and air (Verheij, 1992).

parameters such as: material, size, form, stiffness, load, energy etc.

Consequential product sounds are experienced as "noisy". It is very difficult for users, for designers, and for acoustical engineers to verbally express how they experience a sound. Several problems exist. In general, users lack the vocabulary to express themselves to explain what is wrong or right with a sound. They normally will say the product makes a unpleasant sound or noise. Designers also lack the vocabulary to express design concepts that may also be used in the design of a sound. The acoustical engineers have a very technical vocabulary from the disciplines of physics and sometimes psychoacoustics, which does not communicate very well to designers and to users. In addition, to understand the aesthetic and emotional experience of product sounds knowledge from the field of psychology (auditory perception, cognition, and emotion theories) is needed. As stated before, product sounds are loud and noisy. This inherent property makes it difficult to describe the sound in a structural manner. The reason for this is, of course, that noise by itself is random and lacks structure. However, product sounds do not produce completely random noise due to the resonance and engine/ boiler properties of products (of course, there are many sources that are responsible for the generation of sound in domestic appliances). It is the aim of this product sound course of Industrial design Engineering(IDE), Delft University of Technology (DUT) to try to relate descriptive aspects from the physical, perceptual, and experiential domain to each other in order to improve the sound of domestic appliances.

#### **1.1. The perception of sound**

The top-down processing (involving knowledge stored in memory or mental representations) will result in the attribution of meaning (e.g., recognition, identification), relating sound to certain events, evoking (cognitive) emotions. It is important to note that the sensorial experi‐ ence of a sound can be — often — directly related to the spectral and temporal features of a sound, whereas this is more difficult for top-down aspects (except for very well-structured sounds like speech and music). As described above, one of the aspects that is well known is the irritation that sounds evoke. The irritation can often be contributed to the sensorial processing of the sounds. It can be argued that top-down aspects, like the attribution of meaning, can positively influence the experience whether a sound is irritating or not.

In courses, students hear the sound of an epilator. This sound evokes a rattling and rough experience. If the students are asked to tell the source of the sound most students say this sound stems from a hedge-trimmer or some other power tool. If they are told that it is an epilator and they listen to the sound for a second time, the look on their face is complete‐ ly different and reveals a sense of unpleasantness. Thus, the experience of a sound changes if the meaning is known. One of the perceptual aspects that cause this is the rattling of the product caused by the construction, the gears, and the engine. This aspect can be cap‐ tured by the measure of roughness. This attribute can be related to the structural proper‐ ties of the sound in spectral and temporal domains and is one of the determinants in the perception of sensory pleasantness.
